ENERGY VALUE OF FOODS

• • • basis and derivation

UNITED STATES DEPARTMENT OF AGRICULTURE Agriculture Handbook No. 74 {^^^■■¡■■■^■■■B 887524

ENERGY VALUE OF FOODS

. . . basis and derivation

by

Annabel L. Merrill

Bernice K. Watt

Human Nutrition Research Branch

AGRICULTURAL RESEARCH SERVICE

UNITED STATES DEPARTMENT OF AGRICULTURE

Agriculture Handbook No. 74—March 1955 ^^B^HB

For sale by the Superintendenf of Documents, U. S. Government Printins Office, Washinston 25, D. C. - Price 55 cents CONTENTS Page Page Introduction 1 Part III. Derivation of current calorie factors _ _ _ - 24 Part I. Sources of food energy- 1 Physiological fuel values of foods of animal Fat- 2 origin 26 Determination of fat content 2 Physiological fuel values of plant products 26 Heat of combustion 2 Products of wheat 27 Carbohydrate 2 Products of grain other than wheat 31 Determination of carbohydrate content 2 Legumes 36 Heat of combustion 3 Nuts 36 Protein 4 Vegetables 37 Determination of protein content 4 Fruits 40 Heat of combustion 4 Miscellaneous foods 40 Determined versus calculated gross energy values Part IV. Application of calorie factors _- 43 of foods Comparison of calculated and determined avail- Other sources of energy able calories for diets 44 Organic acids 6 General factors and more specific factors for Alcohol 7 calculating calories in individual foods 48 Part II. Digestibility and available energy of foods._ 8 Application of general factors to national food supplies 48 Definition of terms _. 8 51 Digestibility of fat, carbohydrate, and protein 8 Conclusions Literature cited 51 Availability of energy from digested nutrients 9 Appendix. Tabular summary of experiments on Fat 9 digestibihty of foods of plant origin by human Carbohydrate 10 subjects 58 Protein 10 Apparent digestibility and available energy 58 Alcohol 18 Composition and heat of combustion of foods— 100 Text Tables 1. Average determined heats of combustion of 12. Effects on energy metabolism of replacing fats and oils and assumed factors for fat of portions of dietary carbohydrate and fat by different groups of food materials alcohol 22 2. Average determined heats of combustion of 13. Data used for calculating energy values of foods different carbohydrates and assumed factors or food groups by the Atwater system 25 for carbohydrates of different groups of food 14. Energy values of wheat flours calculated by use materials of specific energy factors for protein, fat, and 3. Factors for calculating protein from nitrogen carbohydrate. 28 content of food 4. Average determined heats of combustion of 15. Apparent digestibility and physiological fuel proteids and nonproteids and calculated heat value of wheat flours 29 of combustion of protein 16. Coefficients of apparent digestibility for grain 5. Comparison of calculated heats of combustion products 32 with results of direct determinations 17. Comparison of determined and calculated gross 6. Fresh fruits classified as to organic acid content. energy values of potatoes 38 7. Factors for heats of combustion and fuel values of nutrients in different groups of food mate- 18. Summary of steps for checking available rials and in mixed diet 10 energy values calculated by factors from 8. Summary of data showing calorie-nitrogen ratio table 13 44 of urine based on early studies of energy 19. Comparison of determined and calculated metabolism and digestibility 12 available energy values of various types of 9. Daily food intake in the experiments from which diets 46 Atwater originally obtained the calorie- nitrogen ratio of 7.9 for urine 16 20. Factors for digestibility, heats of combustion, 10. Daily nutrient intake in the experiments from and physiological fuel values of nutrients in which Atwater originally obtained the calorie- food groups as used in present-day mixed nitrogen ratio of 7.9 for urine 17 diets 49 11 Comparison of data for available energy 21. Comparison of energy values for different obtained by direct determination only and dietary patterns calculated with specific and in part by calculation 19 with general calorie factors 50 Appendix Tables 22. Use of digestibility data to determine coeffi- 23. Apparent digestibility, etc.—Continued cients of apparent digestibility and available Vegetables, vegetable products 94 energy 59 Fruits 98 23. Apparent digestibility and available energy of Miscellaneous foods of plant origin for human subjects.- 60 24. Composition and heat of combustion of food Grains, grain products 60 items used in experiments on human digest- Legumes and nuts 87 ibility (table 23) 100 Energy value of íoods

. . . basis and derivation INTRODUCTION Accurate evaluation of the energy value of foods tions and misuse when apphed to individual foods is essential for dealing with problems of normal and diJSFerent tjipes of diets {114, 115)} nutrition, undernutrition, or obesity. The classic The Food and Agriculture Organization, faced investigations of Professor W. 0. Atwater and his with the -urgency of assessing energy values of food associates at the Storrs (Conn.) Agricultural Ex- supplies in various countries and population groups, periment Station some 50 years ago provided the convened an ad hoc committee of experts in 1947 basis used in this country for measuring the energy to study the problems involved and to make values of food. The general calorie factors 4, 9, 4 recommendations. While endorsing the Atwater developed from that work gained widespread method as one that in the light of present knowl- acceptance, and until recently they were used for edge is suitable if properly used, the committee calculating the calories shown in official food com- pointed out the limitations of the use of general position tables. Properly applied, these general factors and the need for more specific calorie factors provide a satisfactory measure of available factors {65) when dealing with individual foods. energy in average diets and food supplies in this These developments have pointed to the need country. Following Atwater's period little atten- for summarizing the kinds of information Atwater tion was given to methods of calculating food used, the steps followed in his procedure for deter- energy and to the details of Atwater's procedure. mining fuel values of food, and the need for revising However, in recent years attention has again calorie data for foods to take account of additional turned to the important problems of determining research accumulating since his time. This pub- and meeting man^s energy needs. In attempts to lication has been prepared to provide more back- alleviate food shortages experienced duiing and ground information on food energy data than that following World War II consideration was given given in current textbooks and food tables and to first to meeting energy needs in stricken areas. show the basic data drawn upon in deriving the Maynard; who represented this government in revised calorie factors now used in tables of food various interallied food-planning groups, pointed composition in this country. Except for a few out the necessity of understanding the bases of recent revisions, factors derived as shown in this the different methods for estimating energy values publication have been used in U. S. Department of in use in Canada, the United Kingdom, and in Agriculture Handbooks No. 8 {185) and No. 34 this coimtry. On several occasions he called at- {100) and in various other sources, including food tention to the correct application of the general tables published by the lood and Agriculture calorie factors 4, 9, 4 and pointed out their limita- Organization {36), PART I. SOURCES OF FOOD ENERGY The chief food sources of energy to the human urea. Thus protein is incompletely oxidized in body are fat, carbohydrate, and protein. Fats the body, whereas it can be completely oxidizedfin and carbohydrates contain carbon and hydrogen the calorimeter. The heat released by oxidation which can be oxidized to their end products, CO2 of food in the bomb calorimeter is its heat of and H2O, both in the bomb calorimeter and in the combustion and is a measure of its gross energy body. In addition, protein contains nitrogen. value. This nitrogen together with some carbon and Rubner {147), as early as 1885, realized that hydrogen leaves the body chiefly in the form of each of these broad groups of energy-yielding components of foods consisted of substances of ^ The authors express appreciation to Mildred Adams more or less unlike composition and that the heat for her review of the manuscript and her invaluable sug- values for pure protein, neutral fat, and pure gestions; to William Kunerth for his generous help in translating numerous articles from German; and to Blanche C. Spears for her collaboration in various phases of the 2 Italic figures in parentheses refer to Literature Cited, study. p. 51.

1 carbohydrate might not be applicable to foods. mutton, and pork fat have been found to have He also recognized that methods of determining heats of combustion of 9.50 or 9.51 calories per how much of each is present in a food were not gram; butterfat, 9.27; and the fats from several entirely satisfactory. Innumerable improvements common plant sources, about 9.3. Lower figures in methods and techniques for separating and for heats of combustion have been found for total determining the fractions making up these three ether extract, indicating that the extractable main sources of energy in food have been made in matter other than the glycerides has a lower heat the intervening years, but many of the limitations value than the glycerides alone. of determining and dealing with the main sources Atwater {17) applied the heat of combustion of energy in food that were pointed out in 1890 factors determined for triglycérides to crude fat by an ad hoc Committee of the Association of on the assumption that the error resulting from Official Agricultural Chemists {5) still remain. the use of the higher heat of combustion factors In the following sections the terms as they are would in some measure offset the error resulting used today in tables of food composition are from the incomplete extraction of fat in the deter- discussed so that their meaning and limitations mination of the fat content of the food. The will be better understood. table containing the data which Atwater as- sembled from the literature and from his own Fat work and the heat values he considered best suited to apply to the fat content (ether extract) Determination of fat content has been reproduced here as table 1. The fat content of foods usually is determined by one of three general methods: (1) simple ex- TABLE 1.—Average determined heats oj combustion traction with a solvent, (2) acid hydrolysis with of fats and oils as assumed factors for fat of dif- extraction, and (3) saponification with extraction. ferent groups of food materials The fat content reported for foods in American tables of composition refers as a rule to the weight Heat of combustion per gram of crude fat and is obtained by simple extraction Kind of material Assumed or with a solvent, usually ether. Included with the Determined calculated fatty acids and the true fats (triglycérides) thus extracted are other materials having similar Calories Calories Beeffat._ .__ _.. ___ __ 9.50 solubility, such as the sterols, and chlorophyll and Beef "ether extract" __ _ 9.24 some other pigments. Special precautions are Mutton fat 9. 51 necessary to insure complete extraction; carbo- Mutton, ''ether extract". 9.32 hydrate-containing foods, particularly those high Pork fat. .______. 9.50 in starch, present additional problems {61, 66, 105, Pork, ''ether extract". __ _ _ 9. 13 Lard 9.59 Cottolene. 9.32 A method based on acid hydrolysis before ex- Butterfat- _. 9.27 traction gives, in addition to substances listed Wheat oil 9.36 above, fats which are in combination or which for Wheat, "ether extract" _ 9.07 Rye oil-_ 9. 32 other reasons are not removed by the usual fat Rye, "ether extract"- _ 9.20 solvents. Egg and yeast have been showQ to Maize oil 9.28 contain appreciable amounts of fat not extracted Oats, "ether extract" 8.93 without preliminary hydrolysis (75). Barley, "ether extract" .- 9.07 Nut oil (except cocoanut) _ _ 9. 49 The third procedure used in determining the Olive oil _ _ 9. 47 fat content of a food, saponification, is usually Cocoanut oil 9.07 followed by extraction and titration of the fatty Fat of meat, fish, eggs, etc__ _ . 9 50 acids. The data obtained by this method are Fat of dairy products- _ _- 9 25 Fat of cereals- ___ _ 9 30 translated into terms of total fat on the assump- Fat of vegetables and fruits __ tion that all the fatty acids are present as 9. 30 triglycérides. NOTE.—This table appears as table 7 in The Avail- The determination of fat in foods is fraught ability and Fuel Value of Food Materials (17). with complications. Particular care is necessary to avoid oxidation of fat during sample prepara- tion aod analysis, loss of volatile fatty acids, and Carbohydrate the possible formation of esters of fatty acids with alcohol. Determination of carbohydrate content Heat of combustion The difference between 100 and the sum of the crude protein and fat, moisture, and ash is caUed The heat of combustion of the ether extract ''total carbohydrate'' or ''carbohydrate by dif- from a food depends on the particular fatty acids ference,'' a practice used by Atwater in his food making up the triglycérides and on the compo- tables and contiaued in this country. In addition nents and proportions of the other ether-extract- to the true carbohydrates, this "difference" frac- able materials present. The triglycérides of beef. tion may include such compounds as organic acids. Foods of animal origin, except the milk prod- he considered that the carbohydrate'portion of the ucts, contain little carbohydrate. Foods of plant latter consisted mainly of starch. origin, on the other hand, have a variety of car- In many vegetables the carbohydrate is largely bohydrates. The principal ones are starch, sug- starch and cellulose with more or less sugar. ars, and cellulose, but appreciable amounts of Atwater suggested the same calorie factor for pentosans, dextrins, gums, and other carbohy- vegetables that he had used for cereals and for drates also may be present. It has been general- legumes, 4.2 calories per gram. He thought that ly assumed that the starches, at least when vegetables had a higher proportion of pentosans cooked, and the monosaccharides and disaccha- than the cereals and that the higher heat of com- rides are well used by the body. Much less is bustion of pentosans as compared with polyhexoses known about the utilization of cellulose, pento- might offset the lower heat value of the sugars. sans, and other of the more complex carbohy- In fruits a large proportion of the carbohydrate drates. is present as sugar, especially monosaccharides, ^^Carbohydrate by difference'' has been shown but some starch, cellulose, and pentosans also are to be generally satisfactory for estimating energy present. Combining the lower heat of combustion values of foods (17). However, for certaia pur- of the sugars with the higher value for starch, poses, such as dietary planning for the diabetic, Atwater considered that 4.0 calories per gram was carbohydrate values are needed which exclude the probably not far from a correct figure for carbo- fractions that are not potential glucose formers. hydrate in fruits. For these purposes nitrogen-free extract, '^carbo- The main carbohydrate of animal source is mük hydrate by difference" minus fiber, may be calcu- sugar. Atwater found that figures on record for lated. As the digestibility of fiber may be very its heat of combustion were not in agreement and low, nitrogen-free extract is considered a much he used 3.9 calories per gram. Muscle meats and closer estimate of the sum of potential glucose fish contain traces of glycogen, which in ordinary formers than the ''carbohydrate by difference.'' analyses is not taken into account. Oysters, other ''Nitrogen-free extract," sometimes abbreviated to shellfish, and liver, however, may contain an ap- NFE or Nifext, has been used for classifying fruits preciable amount of glycogen, which has a heat of and vegetables into different carbohydrate groups combustion of 4.2 calories per gram. Since the (2,37). amounts of these foods contained in ordinary diets Another approach has been the determination of were small, Atwater used 3.9 calories per gram of the sum of the sugars, starches, and dextrins carbohydrate in all foods of animal origin for gen- measured as total reducing sugars but exclusive of eral dietary calculations. pentoses and hemicelluloses. In such cases it is The table prepared by Atwater summarizing fairly common to report total reducing sugars ex- data on heats of combustion to apply to carbohy- pressed as glucose based on analyses in which cop- drate is reproduced here as table 2. per was used. For routine determinations, this TABLE 2.—Average determined heats of combustion procedure is not entirely satisfactory since the ex- of different carbohydrates and assumed factors for tent of the reduction of the copper reagent differs for the various sugars, and mixtures of sugars may carbohydrates of different groups of food materials be present. In addition the determination may Heat of combustion per gram be complicated by the presence of noncarbohy- Kind of material Assumed or drate reducing substances. Improvements have Determined calculated been made in procedures involving the use of cop- per reagents, and progress is also being made in Calories Calories the development of totally different methods which Pentoses ^ 3. 72 to 4. 38 may some day provide the specific information Dextrose 3. 75 needed. For example, differential fermentation, Lévulose 3. 76 Cane sugar 3.96 Chromatographie separation, and differential spec- Milk sugar 3. 86 trographic analysis give promise of quantitative Cellulose 4.20 determinations for specific carbohydrates. Starch 4.20 Dextrin 4. 11 Glycogen 4. 19 Heat of combustion Carbohydrates of animal Atwater assumed that 97 percent of the carbo- foods, meats, dairy prod- ucts, etc 3.90 hydrate in flours and meals was composed of starch Carbohydrates of cereals 4.20 with a small amount of fiber, about 2 percent Carbohydrates of legumes 4.20 Sugars 3.95 dextrin, and 1 percent sugar. As the heats of 4.20 combustion of dextrin, 4.11, and of sucrose, 3.96, Starches Carbohydrates of vegetables. 4.20 are not greatly different from that for starch, 4.2, Carbohydrates of fruits 4.00 he considered 4.2 calories per gram the suitable factor to use for carbohydrate in cereal foods. He 1 Apparently includes not only the simple pentoses but also applied this figure to the carbohydrate content also the pentosans. of foods consisting largely of starch, such as corn- NOTE.—This table appears as table 8 in The AvailabiUty starch and tapioca, and to dried legumes because and Fuel Value of Food Materials {17). derived by applying the appropriate factor to the Protein total nitrogen present. This procedure mvolves Determination oí protein content the assumption that all of the nitrogen present is in the form of protein, which is not wholly valid It is customary in this country to calculate the because in this procedure counted with the true protein content of a product from the nitrogen protein may be other nitrogenous compounds, present by applying a factor considered suitable such as nitrates, nitrites, purine bases, cholme, for converting nitrogen to the protein in the and free amino acids. particular food. The factors used are based on the nitrogen content of the predominating pro- Heat of combustion tein present in various foods. As a great many The heat of combustion of the nitrogenous commonly occurring proteins contain approximate- portion of food depends on the kinds of protein ly 16 percent nitrogen, 6.25 is the factor often used present and on the proportion of protein and non- for general purposes. In the course of extensive protein nitrogenous material—the latter usually investigations, however, Jones (76) found rather having lower heat of combustion than the former. wide variation in the nitrogen content of different Atwater's procedure for obtaining a figure for kinds of protein, for example, 13.4 percent for an the heat of combustion for the total nitrogenous alcohol-alkali-soluble protein preparation from portion of a food may be illustrated by his figures avocado and 19.3 for amandin in almonds. He for cereal grains having 17.5 percent nitrogen in therefore prepared special factors for converting their proteins. The protein would therefore be nitrogen to protein in those foods for which he computed by multiplying the nitrogen by the considered there was sufficient information to justi- factor 5.7. He assumed, from analyses of Teller fy their derivation. Table 3 lists these factors (4), Snyder (163), and Wiley (183), that not less along with others obtained from him through than 96 percent of the nitrogen of the seeds of personal communication. cereals was in the form of protein and not over 4 percent as nonprotein material. One gram of TABLE 3.—Factors ior calculating protein from cereal nitrogen, then, would be equivalent to nitrogen content of food ^ 5.47 grams of protein (0.96 gm. N X 5.7) and, using asparagin (21.2 percent N) as a model of Food Factor Food Factor the nonprotein nitrogenous fraction, 0.19 grams of asparagin (0.04 gm. N X 4.7). Animal origin: Plant origin—Con. Applying to the protein portion the heat of Eees 6. 25 Legumes—Con. Gelatin 5.55 Beans—Con. combustion of the principal proteins in the cereals, Meat 6.25 Soybeans 5.71 about 5.9 calories per gram according to Atwater's Milk. - 6.38 Velvetbeans_ 6. 25 data, and to the nonprotein portion, the heat of Plant origin: Peanuts 5. 46 combustion of asparagin, 3.45 calories per gram, Grains and cereals: Nuts: Barley 5.83 Almonds 5. 18 the total heat of combustion for the nitrogen- Corn (maize) __ 6.25 Brazil 5.46 containing compounds in cereals was calculated Millets 5.83 Butternuts 5. 30 as follows: Oats 5.83 Cashew 5. 30 Rice 5. 95 Chestnuts 5. 30 5.47 gm. protein X 5.9 cal./gm. = 32.27 calories Rye 5.83 Coconuts 5. 30 .19 gm. asparagin X 3.45 caL/gm. = .655 calories Sorghums b. 25 Hazelnuts 5. 30 Wheat: Hickory 5. 30 5.66 gm. nitrogenous compounds = 32.9 calories Whole kernel- 5.83 Pecans 5.30 1.0 gm. nitrogenous portion=5.8 calories Bran 6.31 Pine nuts 5. 30 Embryo 5.80 Pistachio 5.30 For the heat of combustion of the nitrogenous Endosperm. _ 5. 70 Walnuts 5.30 portion of meat, Atwater felt the most satisfactory Legumes: Seeds: procedure was to use the value for the fat-free Beans: Cantaloup 5. 30 muscle tissue including the nonprotein extractives, Adzuki 6.25 Cottonseed 6.30 Castor 5.30 Flaxseed 5.30 as quantitative data on creatin and other non- Jack 6.25 Hempseed 5.30 protein compounds were lacking. The heat of Lima 6.25 Pumpkin 5.30 combustion for fat-free muscle meat was about Mung 6.25 Sesame 5. 30 5.65 calories. He used this same factor for the Navy 6.25 Sunflower 5.30 protein of milk. He estimated the heat of com- bustion for the nitrogenous portion of egg to be 1 Adapted from table 5 of U. S. Department of Agricul- 5.75 calories per gram, based on data for proteins ture Circular 183, revised edition, February 1941 (76) and from unpublished data obtained by personal communica- in the white and yolk, assuming that very little tion with the author. For groups of foods not included nonprotein nitrogen is present. here, the conventional factor 6.25 should be used until Table 4 is a reproduction of one prepared by more is known regarding their proteins. Atwater showing average determined heat of com- bustion of '^proteids" and ^^nonproteids'^ and The figures commonly reported in American calculated heat of combustion of "protein.'' At- tables of composition for protein actually repre- water used the term "proteid" to cover the true sent crude protein, since as a rule the figures are proteins, and the term "protein" to cover both the nonprotein compounds, the extractives, amides, food can be shown by using potatoes as an ex- etc., and the true proteins. If Atwater's heat of ample—a food known to contain a considerable combustion values for protein (as defined by him) portion of nonprotein nitrogen. If 60 percent of is applied to protein as currently determined, that potato nitrogen is attributed to protein and 40 is, total N times a factor, some error will result percent to asparagin, the heat of combustion of the because the heat of combustion of the true proteins nitrogenous matter equivalent to 1 gram of nitro- is usually higher than that of other nitrogenous gen should be 28.2 calories and the heat of com- compounds. It has become the custom in this bustion per gram of nitrogenous compounds, 5.01 country, however, to apply heat of combustion calories, as shown by the calculations below: factors to total nitrogen treated as protein without weighting the composition data according to the 0.6 gm. NX6.25 = 3.75 gm. protein proportion of the different nitrogen-containing 0.4 gm. NX4.7=^1.88 gm. asparagin compounds present. This has been done because 1.0 gm. N=5.63 gm. nitrogenous compounds of the limited information available on the parti- 3.75 gm. proteinX5.8 cal./gm.=21.75 calories tion of nitrogen in foods between true protein and other forms. Although this procedure may re- 1.88 gm. asparaginX3.45 cal./gm.^6.49 calories sult in an appreciable error in the calorie value of 5.63 gm. nitrogenous compounds=28.24 calories the protein of a food, the error in the total energy value is generally small, as most foods having a 1.0 gm. nitrogenous compounds=5.02 calories large proportion of their nitrogen as nonprotein jf however, all of the nitrogen is assumed to be lutrogen (mostly vegetables and fruits) contam p^^^^-^^^ (^ 25 gm. protein) and to this is appUed relatively small amounts of total mtrogen. ^^^^ f^^^^^. 5 Q2 calories (corrected as shown above .rn A A j • 7 I r r ' fo^ thc lowcr hcat of combustion for the nonpro- TABLE 4..--Average determined heats of combustión ^^;^^ portion), an energy value of 31.4 calories per ofproteids and nonproteids and calculated heat of ^^^^ nitrogen results \l X 6 25 X 5.02) This combustion of protein ^^3^1^ -g ^bout 11 percent higher than that ob- tained in the first calculation because the content Heat of combustion per gram ^^ protcln is Overestimated. If no correction is Kind of material A.um d r made for the presence of nonprotein nitrogenous Determined cScSated"^ compouuds and if the higher heat of combustion of potato protein, 5.8 calories per gram, is applied, Calories Calories an energy value equivalent to 36.25 calories per Beef, fat-free muscle 5. 65 Beef, fat-free muscle, extract- gram of nitrogen would result (1 X 6.25 X 5.8). ives removed 5.73 This result is nearly 30 percent higher than the Teal, fat-free muscle 5. 65 first calculation because there has been overesti- Mutton, fat-free muscle 5. 60 mation in both the content of protein and the heat Protein of meat ^' ^^ of combustion of the nonprotein fraction. This F]gg albumin 5.71 Egg, protein of yolk 5.84 [lllllllll illustration shows that we should have data on Yitellin 5. 76 the actual partition products, but until we do, it Protein of egg S- 75 seems best to continue the rather arbitrary pro- Milk casein 5. 63 to 5. 86 cedure shown here as the second calculation, Milk protein 5. 67 Protein of dairy products 5.'65 namely, to apply a weighted calorie factor to total Gliadin 5.92 nitrogen treated as protein. -Glutenin 5.88 ■Gluten of wheat 5. 95 Legumin 5.79 Determined versus calculated gross Plant fibrin 5.89 Protein of cereals (96% pro- energy values or roods teids) 5.80 Protein of legumes (96% pro- Gross energy may be determined directly by teids) ^' ^^ burning a sample of food, or it may be calculated Protein of vegetables (60% proteids) 5 00 by applying previously determined heats of com- Protein of fruits (70% pro- bustion to composition data on the energy-yielding teids) 5- 20 components of food and obtaining the sum. Gelatin 5.27 In view, however, of the diversity within the Greatin, as type of non-pro- teids of animal foods 4. 27 fractions of the so-called protein, fat, and total Asparagin, as type of non- carbohydrate components of food pointed out m proteids of vegetable foods.. 3. 45 preceding paragraphs, and in view of the assump- tions made in deriving heat of combustion values Note.-This table appears as table 6 in The Availability to apply to each fraction, Atwater recognized the and Fuel Value of Food Materials (17). importance of checking the gross energy values calculated for foods. He compared results ior The effect of method of calculation on estimated calculated and determined gross heats of combus- energy values for the nitrogenous compounds in a tion for 276 samples mcludmg foods ot animal origin as well as a variety of plant products. He We have compiled gross calorie data for a found that when he applied the heats of com- number of samples of wheat and flours produceü bustion he had worked out for protein (actually in this country. For 15 samples of wheat or whme- nitrogenous compounds), fat (as ether extract), wheat flour reported in the literature {164^ P^y and carbohydrate (usually determined by differ- 168,183,194, 195) differences between determined ence) to amounts present, the results were in good and calculated gross heats varied from 0.1 percent agreement with those obtained by bomb calo- to 1.9 percent and averaged only 0.6 percent. J^or rimeter. Although in a few cases discrepancies 16 additional samples of wheat flour of varymg were as much as 5 or 6 percent, agreement was degrees of refinement the average difference very much closer in most cases and justified the between gross calories obtained the two ways was use of the calculated values. slightly higher, 1.3 percent. The table in which Atwater summarized these comparisons has been reproduced here as table 5. Other sources of energy Possibly the difficulties in getting satisfactory composition data for dried samples of high original Two other sources of energy—organic acids and water content was responsible for the larger discrepancies observed between the calculated alcohol—are noted below since in some circum- and determined gross heats of combustion for stauces one or both may be important. fruits and vegetables. Differences might be expected for milk likewise and may have been Organic acids observed for individual samples, but the averages Occurrence of organic acids.—Organic acids for the 37 samples are in excellent agreement. are widely distributed in foods but for the most With the improved techniques in moisture deter- part in small concentrations. Among the various minations now available, we would expect even acids that have been identified are: Malic, citric, better agreement between the gross heats obtained isocitric, ascorbic, oxalic, lactic, succinic, acetic, by calculation and the determined values. quinic, tartaric, benzoic, glyoxalic, sahcylic, aconi- tic, and malonic. As explained earlier, figures for TABLE 5.—Comparison oj calculated heats oj the total carbohydrate content of a food, that is, combustion with results oj direct determinations ''carbohydrate by difference,'' include organic acids. In a very few foods the acids are suflEi- Average heat of Calcu- ciently abundant that they should be determined Number combustion per lated of gram of water- results separately for estimations of energy values of anal- free substance in per- Kind of food material yses in- centages those foods, inasmuch as they are distinctly differ- cluded of those ent chemically from carbohydrates and their heats in Deter- Calcu- deter- average mined lated mined of combustion are lower than for carbohydrates generally. Total free acid is commonly deter- Calories Calories Percent mined by titration against standard alkali and Beef 55 6507 6619 101. 7 expressed as the predominant acid in the food. Beef, canned 7 6197 6268 101.2 Mutton 10 7146 7316 102. 4 To the extent that the organic acids may be Pork 10 7835 7944 101. 4 present in bound form the total acid value may be Poultry 5 6310 6508 103. 1 underestimated, but this error is ordinarily con- Fish 3 6317 6427 101. 8 sidered of little importance. Eggs 10 7103 7160 100.8 Butter 20 8832 8918 101.0 Fruits contain organic acids in more significant Milk 37 5437 5413 99. 6 amounts than other food groups. In table 6 a Breakfast foods 3 4367 4360 99.8 number of fruits have been classified according to Bread, crackers, etc 36 4536 4513 99. 5 Corn (maize) meal and corn the total free organic acid content as reported in preparations 7 4580 4624 101.0 the literature. Citric and malic acids predomi- Rye preparations 6 4353 4343 99.8 nate in all fruits listed except grapes and tamarind. Barley preparations 2 4352 4365 100.3 Tartaric acid accounts for most of the total in Rice 5 4390 4474 101. 9 Oatmeal (rolled oats) 2 4834 4811 99.5 these two fruits. Other organic acids have been Oatmeal, cooked 6 4488 4480 99. 8 found present in small amounts in fruits. Of the Wheat, pastry 8 4579 4605 100. 6 fruits listed in table 6 only 7 have been re- Legumes, fresh 8 4367 4361 99. 9 ported to contain more than 2 percent organic Legumes, cooked 5 4312 4343 100.7 Vegetables, fresh 10 4195 4051 96. 6 acid; 15 contain from 1 to 2 percent; and more than Vegetables, cooked 3 4057 4277 105.4 35 contain less than 1 percent. However, in pro- Vegetables, canned 2 4264 4102 96.2 portion to the total solids, the organic acids may Fruits, fresh 12 4389 4123 93.9 provide an appreciable percentage of the total Fruits, canned 4 4078 4056 99.5 Average 276 samples 100.3 energy value of some fruits. For lemon juice, it would amount to over half, but for peaches, only about a twentieth. jQ-ote.—This table appears as table 9 in The Availability and Fuel Value of Food Materials {17). Figures for heat Less information is available on the acid con- of combustion are in terms of small or gram calories rather stituents of vegetables, but the amounts in most than large or kilogram calories customarily used for foods. vegetables tend to be less than 0.5 percent. TABLE 6.—Fresh fruits classified as to organic acid content ^

3 percent and over 3 2 to 3 percent 1 to 2 percent 0.5 to 1 percent Less than 0.6 percent

Lemons (C). Cranberries (C). Apricots (M). Apples (summer) (M). Apples (fall) (M). Limes (C). Currents, red, black, Carissa or natal plums Blackberries (C). Apples (winter) (M). Tamarind (T). and white (C). (C). Blueberries (C). Bananas (M). Gooseberries (C). Cherries, sour (M). Cherries, sweet (M). Cherimoya (C). Grandillas, purple, or Grapefruit, all (C). Crab apples (M). Feijoa (C). passion fruit (C). Groundcherries (in- Grapes, pulp or juice, Figs (C). cluding poha and American type, all Jujubes (C). cape-gooseberry) (C). (T). Limes, sweet (C). Kumquats (C). Grapes, European type, Muskmelons (C). Loganberries (C). all (T). Papayas (C). Loquats (C). Guavas (C). Pears, all (C). Nectarines (M). Mamey or Mammee Persimmons, Japanese Oranges (C). apple (C). or Kaki (M). Plums, excluding Mangos (C). Persimmons, native prunes (M). Mulberries, black, (M). Pomegranates (C), white, and red (M). Prickly pears (M). Raspberries, red and Peaches, all (M). Roseapples (C). black (C). Pineapples (C). Sapodilla or sapota (C). Strawberries (C). Plantains (M). Sapote or Marmalade Tangerines, other Prunes (M). plum (C). Mandarin type Quinces (M). Sugar apples or oranges (C). sweetsop (C). Watermelons (M).

1 Total free acid expressed in terms of the predominating acid as malic (M), anhydrous citric (C), or tartaric (T) in the edible portion of fruit. 2 Lemons and limes, 6 percent; tamarind, ripe, 13 percent.

Hartman and Hillig (63) ^ reporting results from available, the heats of combustion or gross calorie analyses of organic acids in a large number of food values per gram of acid calculated from gram- products, included a table of 29 vegetables which molecular weight data are as foUows: showed a total malic and citric acid content (free Calories and combined) ranging from 0.1 to 0.8 percent. Acid: per gram Only for lima beans, cauliflower, white potatoes Acetic 3. 488 (Idaho), and tomatoes were the values above 0.5 Citric 2. 471 Lactic 3. 620 percent. Malic 2. 388 In certain types of processing by fermentation the total acidity of the product is increased several Organic acids contribute a very small portion fold over the original content of the food. Cab- of the total daily calorie intake, but in a few bage, for example, contains only a fraction of a foods they are present in amounts that should not percent of acid as malic and citric, while sauer- be overlooked as potential sources of energy. lo-aut has around 1.5 percent lactic acid. Simi- The gross energy value of organic acids in 100 larly apples contain less than 1 percent acid grams of a few foods has been estimated as follows : expressed as malic, but vinegar made from apples Food: Calories averages about 4.5 percent acetic acid. Lemons, limes 15 Some of the acid constituents of food are Currants, gooseberries 6 Fruits, 1-2 percent group (see table 6) 2.5 to 5 available to the body as a source of calories; Apple vinegar 16 others are known to be unavailable or of doubtful Sauerkraut 5 availability. Oxalic acid is probably excreted in the form of its insoluble calcium salt; tartaric Alcohol acid is thought to be either excreted unchanged or destroyed by micro-organisms. Little is known Alcohol, with a gross energy value of 7.07 about the availability of such acids as glyoxalic, calories per gram, is another source of energy malonic, and aconitic, but since they occur in which may be important in the diet of sonie insignificant amounts they would make a negligible individuals or some population groups. It is contribution to the total energy value of the foods discussed in connection with the availability of in which they are found. energy from the various sources (p. 18) since the Heat of combustion.—For the several acids availability of its fuel value is the point of un- found in appreciable amounts and considered certainty.

305774—55- PART II. DIGESTIBILITY AND AVAILABLE ENERGY OF FOODS (intake—fecal protein) less the gross energy of Définition oí terms the urine. Available energy of a food may be Meanings of some of the terms necessary in a obtained entirely from data on heat of combustion discussion of energy value of foods have changed or it may be calculated in part from analytical over a period of years. In the following para- data on nitrogen according to the foliowing|proce- graphs terms of most importance are explained dures: and attention is called to differences in past and 1. Gross energy of food— (gross energy of urine+ present connotations. feces). Digestibility was the term Atwater used for 2. Gross energy of food — (gross energy in feces+ the proportion of food material actually digested. net absorbed grams NX7.9). If there had been a way to measure the undigested 3. Gross energy of food — (gross energy in feces+ residue in the feces, digestible food would have urinary N in gramsX7.9). been computed as the difference between the total food eaten and the undigested residue. However, If the subject is in nitrogen balance, no difference as he pointed out, methods for distinguishing would be expected in the deduction for urinary between metabolic products in the feces and loss between procedures 2 and 3. A discussion>f undigested residue from the food were not suffici- the extent of the differences resulting from ^these ently accurate to permit the determination of the methods of calculation under other conditions undigested residue separately and he did not follows the section on calorie-nitrogen ratio of the compute digestibility. urine, page 18. Availability was the term Atwater used to Atwater distinguished between physical and designate the quantity or proportion of the food physiological fuel values, the latter being the actual or of the nutrients which could be used for build- benefit gained by the body from the use of fuel for ing and repair of tissue and the yielding of energy. the different purposes served. This distinction Some of the absorbed nutrients are used to form was made in recognition of the possibility that the digestive juices and returned to the tract in the energy value of a gram of fat, for example, might form of hue and other digestive secretions. Inas- be different for mechanical work from what it much as these metabolic products are not used would be if used only for maintaining body heat. for tissue building or as fuel, they are not avail- Atwater used the term fuel value as obtained by able in the sense in which Atwater employed the method 1, 2, or 3 described above to mean physical term. He computed the amounts of available fuel value, not physiological fuel value. The nutrients (protein, fat, carbohydrate) by sub- latter term, however, has since been applied to his tracting the amounts in the feces from the amounts data and to his method of obtaining fuel values in the food. Availability as Atwater used the {65, 111, 169). Likewise, in the present publica- term is the same as apparent digestibility in more tion physiological fuel value is the term used to recent years and in current usage. He calculated connote energy value of a food obtained by sub- the coefficient of availability, using nitrogen for tracting energy lost in the excreta (feces and urine) illustration, as foUows: from the total energy value of the food, no con- N in food—N in feces sideration being given to the specific functions XI00=coefficient of served in the body. N in food availability. According to present usage this would be called Digestibility of fat, carbohydrate, the coefficient of digestibility, meaning of course and protein apparent digestibility, and it corrects only for total fecal losses. On any diet some ether extractable matter, Heat of combustion data are obtained by burning nitrogenous matter, and other organic matter are samples of food in a bomb calorimeter. The heat lost in the feces and must be taken into account in of combustion is a measure of the gross energy calculating the energy value of foods. The nitrog- value of the food. enous matter present in the feces may be due in Available energy of a food takes into account part to undigested food residues, bacteria and their both fecal and urinary losses. The total available products, the residues of digestive juices, and energy of the food is its heat of combustion less mucus or particles of epithelium mechanically that of the lu-inary and fecal residues. For fat separated from the walls of the digestive tract. and carbohydrate the available energy is the gross Numerous studies have been made to determine to energy of the amounts absorbed (intake—fecal what extent the nitrogenous matter in the feces fat and carbohydrate) since each nutrient is under different kinds of dietary conditions is assumed to be completely oxidized. The incom- metabolic and to what extent it is undigested or pletely oxidized matter of the urine is assumed to unabsorbed food material. Some investigators be of protein origin and the available energy of have concluded that all the nitrogenous matter in protein is the gross energy of the absorbed protein the feces results from metabolic processes but that 8 some foods cause greater loss than others {104, 106, 147). Other workers, including Murlin and Food group Protein Fat Carbohy- coworkers {4.0,127,128) and Bricker, Mitchell, and drate Kinsman (Sl), as a preliminary step in obtaining Percent Percent Percent biological values of proteins, have estimated the Animal foods _ _ _ 97 95 98 digestibility of foods with the assumption that Cereals 85 90 98 Legumes, dried 78 90 97 part of the fecal nitrogen is metabolic in origin and Sugars and starches 98 part is from food eaten. Vegetables 83 90 95 Since this publication is concerned primarily Fruits 86 90 90 with estimation of energy value no attempt has Vegetable foods__ 84 90 Q7 been made to distinguish between metabolic and Total food Î ._ 92 95 97 undigested food nitrogen appearing in the feces, because neither is available to the body as a source 1 Weighted by consumption statistics based on a survey of energy. Actually, level of N intake may appre- of 185 dietaries. ciably affect the apparent digestibility of protein; on low levels of protein intake the fecal N may When these coeiBcients were applied to data in represent chiefly metabolic N which, when charged 93 digestion experiments on ordinary mixed dieta against a specific test food, leads to low values for very good agreement was found between calculated apparent digestibility of this food. Results re- values and the results of actual determination. ported in the literature in which digestibilities of The calculated coefficient for protein in the whole test foods were measured under conditions of diet was 93.6, and that found by actual determina- extremely low protein intake are therefore not tion, 93,3; for fat the calculated value was 94.5 satisfactory for application to a more normal level and that found by determination, 95.0; for carbo- of protein intake. Even under conditions of hydrate the calculated value was 98.1 and the higher protein intake, losses attributed to the actual value, 97.7. From this Atwater concluded protein of the test food by this method of calcula- that for average mixed diets the calculated tion may actually be due to the influence of the coefficients were close enough to the determined test food on the digestibility of the entire diet. so that the calculated could be used. But he Similar problems occur in calculating the energy pointed out that the calculated coefficients might factors for carbohydrate and fat {188, 190, 191). not be applicable under all circumstances and More information or possibly an entirely different might not apply to all foods in one class. approach is needed to relate fecal losses directly to Digestibility studies published since his time have the test food. indeed shown rather wide differences among foods Atwater assembled results of many digestion within these groups. experiments on men in which the apparent digesti- A review of the literature shows that in most of bility of a food was studied. In some experi- the experiments very simple diets have been used ments a single food was fed and in others the test in which the test foods made up a large proportion food was fed as part of a simple mixed diet. of the total diet. In experiments where the test From these findings he developed tentative co- foods were fed alone or contributed essentially all efficients of digestibility. As they had been of the nutrients tested, the supplemental action based largely on the digestibility of single foods of one food upon another cannot be observed. in very simple diets, Atwater tested these tentative Woods and Merrill {193) reported that some of coefficients by applying them to the several foods their early digestion experiments with men showed in experiments in which ordinary mixed diets milk and bread to be more completely assimilated were eaten. In these latter experiments the when fed together than when eaten separately. amount of protein, fat, and carbohydrate in the A similar conclusion was reached by Bryant {32) feces was compared with that in the total food so regarding milk and oatmeal when fed together and that the '^ availability'' measured applied to the separately to infants. Unfortunately there is not whole mixed diet and not to nutrients in individual adequate basis at this time for estimating how foods. The results found for these actual ex- significant the differences in digestibility are under periments were then compared with the calculated different conditions of diet intake. results in which the various tentative coefficients for each kind of food had been applied to the quantities of the respective foods in the diet. Availability of energy from digested Atwater reported that some adjustments in the nutrients tentative coefficients were necessary and he altered them slightly in the way he considered most Fat probable. The resulting average coefficients of Atwater illustrated his method of estimating apparent digestibility (availability as Atwater the fuel value of fat (ether extract) with the fat used the term) for the nutrients in different food of meat. The coefficient of digestibility (current groups and for nutrients in a mixed diet were as usage) had been determined to be about 95 per- follows: cent. As its heat of combustion was about 9.5 calones per gram, its fuel value was 9.0 calories every gram of nitrogen present in the urine there per gram (9.5X.95=9.02). was sufl&cient unoxidized matter to yield 7.9 calo- ries, the equivalent of approximately 1.25 calories Carbohydrate (7.9-^6.25) per gram of available (absorbed) pro- tein. The heat of combustion of a gram of ab- The fuel value of carbohydrates was determined sorbed protein (nitrogenous compounds) was in like manner. For example, cereal carbohy- therefore reduced by 1.25 calories per gram to hydrate was considered about 98 percent available allow for incomplete metabolism. In the case of (absorbed) for use in the body, and using the heat digestible meat protein, for example, the heat of of combustion of 4.2 calories per gram, the fuel combustion per gram is 5.65 calories. Of this value was 4.1 calories (4.2X.98=4.12). number, 1.25 would be deducted for the heat of combustion of the unoxidized products in the Protein urine. This figure was derived from the ratio of For protein (nitrogenous products), in addition the calorie value of the urine to the nitrogen con- to the use of the coeflScient of digestibility, it was tent of the urine on the assumption that the sub- necessary to correct for the loss of incompletely jects were in N-equilibrium and that all of the oxidized nitrogen from the body. To do this nonmetabolized part of the available N was re- Atwater determined the ratio of the nitrogen in covered in the urine. The fuel value, 4.40 calo- the urine to the heat of combustion of the urine. ries, would then be applied to each gram of protein The average of 46 determinations showed that for available as a source of fuel. TABLE 7.—Factors jor heats oj combustion andjuel values oj nutrients in different groups of food materials and in mixed diet Fuel value Nutrients Proportion Total energy furnished by Heat of com- of total per gram in Kind of food material each group bustion per nutrient available Per gram per 100 grams gram actually nutrients available Per gram total nutrients Total available nutrients

D F2 = (B X C) F revised ' Protein Orams Calories Calories Calories Calories Calories Meats, fish, etc 43. 0 5.65 0.97 5. 50 4.40 4. 25 4.27 Eggs 6.0 5.75 .97 5. 60 4. 50 4. 35 4.37 Dairy products 12.0 5.65 .97 5.50 4.40 4.25 4.27 Animal food 61. 0 5. 65 97 5. 50 4.40 4. 25 4.27 Cereals 31. 0 5.80 , 85 4.95 4.55 3.70 3.87 Legumes 2.0 5. 70 , 78 4. 45 4. 45 3.20 3.47 Vegetables 5.5 5.00 83 4. 15 3.75 2.90 3. 11 Fruits . 5 5. 20 85 4. 40 3.95 3. 15 3.36 Vegetable food 39.0 5. 65 85 4.80 4. 40 3. 55 3.74 Totalfood 100.0 5. 65 . 92 5. 20 4. 40 4.00 4 05 Fat

Meat and eggs 60. 0 9. 50 95 9. 00 9.50 9.00 9.03 Dairy products 32.0 9. 25 95 8. 80 9. 25 8. 80 8. 79 Animal food 92.0 9. 40 95 8.95 9. 40 8.95 8.93 Vegetable food 8.0 9.30 90 8. 35 9.30 8.35 8. 37 Totalfood loa 0 9. 40 95 8. 90 9.40 8. 90 8.93 Carbohydrates

Animal food 5.0 3.90 ,98 3.80 3.90 3.80 3.82 Cereals 55. 0 4.20 98 4. 10 4. 20 4. 10 4. 11 Legumes LO 4. 20 97 4.05 4.20 4.05 4.07 Vegetables 13. 0 4. 20 95 4.00 4.20 4. 00 3.99 Fruits 5.0 4.00 90 3. 60 4.00 3.60 3.60 Sugars 21.0 3. 95 98 3.85 3.95 3.85 3.87 Vegetable food 95. 0 4. 15 97 4. 00 4. 15 4.00 4. 03 Totalfood 100. 0 4. 15 97 4.00 4. 15 4.00 4.03

1 Values for fats and carbohydrates, same as corre- of combustion values for protein adjusted for energy loss in sponding values in column B. Values for protein, same as the urine by deduction of 1.25.) corresponding values in column B minus 1.25. 2 Values for fats and carbohydrates, same as corre- NOTE.—This table appears as table 10 in The Availa- sponding values in column D. Values for protein, same as bility and Fuel Value of Food Materials {17) with the corresponding values in column D minus 1.25. exception of column F, revised. The figures in this column 3 Proportion of total nutrients available (column C) appear in tabular form in Investigations on the Nutrition applied to heat of combustion values (column B). (Heat of Man in the United States {98, p. 18). 10 The basic data needed for computing fuel value Corrected values for column F were written in of a diet were brought together by Atwater and file copies 3 of the report and have been included Bryant in a table, reproduced here as table 7. as column F revised here in table 7. The cor- They presented two sets of factors for use in esti- rected values were also published by Langworthy mating energy values. In column E of their table and Milner in 1904 in a summary of investigations they listed the factors to apply to a gram of avail- on the nutrition of man in this country (98). This able protein, fat, and carbohydrate in each of the publication may not have had wide circulation various food groups and the average calorie factors and has seldom been cited. The revised values per gram, 4.40, 9.4, and 4.15, to apply to the total make for consistency in the use of columns E and amounts of protein, fat, and carbohydrate avail- F. It should be pointed out that the revised able in a mixed diet. The factors in column E figures for column F were unrounded in contrast to the values in columns D and E in the original were therefore to be appHed to absorbed nutrients. table. The fuel value factors listed in column F in- The calorie value per gram of urinary nitrogen.— cluded a correction for digestibihty loss and were Several questions have been raised on the advis- to be applied to grams of ingested protein, fat, and ability of applying 7.9, the calorie-nitrogen ratio carbohydrate in each of the food groups; the in urine pubhshed by Atwater (12, 17), to energy average factors rounded to 4.0, 8.9, and 4.0 calories calculations for which dietary conditions may be per gram were to be applied to the total amounts greatly different. Lusk (101) summarized data of the nutrients in mixed diets. These then were showing that the ratio was affected by the propor- the factors that they considered could be applied tion of dietary protein, fat, and carbohydrate. directly to representative data on the chemical Other questions have been raised concerning the composition of foods. effect of negative or positive nitrogen balance, and of high-fruit diets having more than the usual For some time after the publication of this work amount of organic acid. of Atwater and Bryant, apparently no consistent Unfortunately, at the present time no record is pohcy was followed with respect to the factors at hand showing the specific experiments from used to estimate energy values of foods {6, 8, 10, which Atwater derived the ratio of 7.9 calories per 18, 19, 20, 68, 89, 157, 169, 171). For a period of gram of urinary nitrogen and from it concluded time the Atwater and Bryant general factors ap- that 1.25 calories per gram of available protein peared in the literatm-e as 4, 8.9, 4; then a refer- should be subtracted for loss of incompletely ence to a further rounding of the factors to 4, 9, 4 oxidized material in the urine. was made in the 1910 revision of Farmers' Bul- As early as 1897 Atwater and Benedict in the Storrs Agricultural Experiment Station report for letin 142 (11), The 4, 9, 4 factors later came into that year (12,. p. 167), stated, '' . , . the heat of widespread usage in estimating calorie values of combustion of the water-free substance of the food and not only were applied to the total m-ine will be 1.25 calories for each gram of digested amounts of protein, fat, and carbohydrate (by (available) protein. This factor is the average difference) of a mixed diet as Atwater and Bryant found in a number of experiments in this labora- had originally intended but also were used in tory, in which the heat of combustion of the assessing the fuel value of individual foods. water-free substance of the urine was determined." Following the publication of the 1899 report, it At the time this statement was published, results was realized that for protein the number of calories probably were available from the first 16 of a series of 55 experiments on the metabolism of calculated by applying factors in column E to matter and energy in the human body conducted absorbed nutrients was not identical with the under Atwater's supervision. We found the ratio number derived by applying factors in column F of the heat of combustion of urine to urinary nitro- to total nutrients. Results obtained by the latter gen when calculated for these 16 experiments to were too low. The error resulted from the misuse average 7.9 calories, or the equivalent of 1.26 cal- of the factor 1.25 derived from a gram of protein. ories per gram of absorbed protein (7.9-^6.25= It had been applied to protein which, after diges- 1.26). tion loss was taken into account, was less than 1 The study that included the 55 metaboHsm gram. To illustrate: If a subject ingests 1.0 experiments was made at Middletown, Conn., during the years 1896-1902 under the auspices gram of protein the gross fuel value of which is of the U. S. Department of Agriculture in coopera- 5.65 calories, and if only 0.97 gram is digested, tion with the Storrs (Conn.) Agricultural Experi- the gross available calories are 0.97X5.65, or 5.48. ment Station and Wesleyan University. The Since only 0.97 gram is available from each gram subjects were normal healthy men of similar of ingested protein, only 0.97X1.25 or 1.21 cal- weight, around 65 to 79 kg. ories should be deducted. Thus for 1 gram of ingested protein, the available energy value would 3 A note on one of the marked copies on file in U. S. be 5.48—1.21, or 4.27 calories. This is the same Department of Agriculture reads, ''A copy showing cor- rections as made on slips sent to Magnus Levy in letter'^of as 0.97 (5.65-1.25). July 6, 1904."

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«3 »^ o . Qy-^^ Oi Cq CO '5Í< lO b- ; « o d s.2-lo tí û; tí o ti.(i (D !>. CQ sL^ «D CD p ^ 7 o OOOSOi-KMC^COrílLOCOt^ iCi—ICOCOÍMCDCOCDCOCDCD «Ü ft.2W o^ o « go^ CD Oi tí j^ tí •gogtí CD ■^'ftS ^ r CD r :::^ ft^ ^ CQ tí ^03^ (M «îcDt; -p < .a "S bo's ËP"S M g-3- d° o ^ pp 00 cd PQ 14 A complete outline of the work, and the pro- closely with results obtained when the urine was cedures followed were given in considerable detail analyzed each day. This assured the investigators by Atwater and Benedict (16). Those aspects of that no significant error occurred from nitrogen the study thought to have a direct bearing on the or energy loss in the urine during storage. calorie-nitrogen ratio of the urine will be referred The heats of combustion were determined by to here. Some additional details are given in the the Kellner method. A weighed absorption block section on alcohol (p. 18). Selected data from of cellulose of known heat of combustion was the 55 experiments have been summarized in saturated with a known amount of urine, dried table 8 along with data from a later series in which at about 60° C, and burned in a bomb calorim- Benedict and Milner continued the study. eter. The results were corrected for the heat Atwater designated the first foiu* experiments of combustion of the absorption block. This latter of the series as "respiration experiments;^' for factor was an average of determinations for a these, analyses were made of food intake, drink, number of similar blocks. The method was given feces, urine, and respiratory products. No deter- in detail by Atwater and Snell, 1903 (22). minations were made of the heat given off from ^ The investigators took into account the possi- the body nor of the heat equivalents of external bility that a lag in nitrogen excretion by the work in these experiments. He called the remain- subjects would introduce some error in urinary ing experiments. Nos. 5 through 55, ''metabolism estimations in the relatively short experimental experiments.'^ They included measurements periods of 3 to 4 days. This possible error was of energy in addition to the data obtained in the reduced by having periods on the same diet run respiration experiments. Each metabolism experi- consecutively. In addition to the incompletely ment had two parts, a digestion experiment in oxidized matter lost iu the urine the perspiration which the subject lived under ordinary conditions losses should be recognized. However, as nitrogen and the metabolism experiment proper in which losses have been shown by 25 work experiments of the subject lived in a respiration chamber. Di- Atwater and Benedict (16) to be small, averaging gestibility data were available from the second only 0.29 gram per day, and as data on compa-^ part as well as from the first part of each metabo- rabie energy loss in the perspiration were lacking,, lism experiment. the data in table 8 apply to urinary losses only. The respiration calorimeter, described in detail The series was plaimed to study metabolism (1) in U. S. Department of Agriculture Bui. 63 (21), while fasting, (2) when the proportions of fat and was especially designed for this series of experi- carbohydrate of an ordinary diet were varied,, ments. It included among other equipment a and (3) when a moderate amount of alcohol bed and a stationary bicycle with an ergometer for replaced fat and carbohydrate isocalorically. In measuring external muscular work, thus providing the first 16 experiments rather simple mixed diets for the study of metabolism of matter and energy were used as shown in table 9. For these experi- under conditions of rest and strenuous activity. ments the amounts of protein, fat, and carbo- In the so-called work experiments, the activity hydrate, and the gross calories found by deter- of the subject varied but in most cases he rode mination were reported. The amounts of other the stationary bicycle for 8 hours daily. During nutrients present in the diet have been calculated the preliminary digestion period, prior to the work from tables of nutrient composition; these cal- periods within the calorimeter, the activity of culated values are shown in table 10. the subject was sometimes comparable to that In the annual report for 1899 (17) Atwater con- during the work period and sometimes was only tinued to use the same factor, 1.25 calories per his normal activity with some additional light gram of digested protein, in his calculations of exercise. This latter activity was designated as available energy, although he recognized that this ''hght'^ in table 8 to differentiate it from the deduction was not accurate for all foods. Some more strenuous activity of pedaling the stationary error is introduced when this correction, based on bicycle for 8 hours daily, referred to as a ''work'' the factor 6.25 to convert nitrogen to protein, is experiment. In the "rest" experiments the subject used with proteins or with nonproteins containing remained quiet, avoiding all muscular activity as more or less than 16 percent nitrogen. In the far as it was practical. same publication he mentioned briefly the deriva- Certain precautions were taken to minimize tion of the basic figure 7.9 calories per gram of errors in the nitrogen and energy determinations. urinary nitrogen. He stated that the figure was The urinary nitrogen was determined in 6-hour based on the average of 46 determinations. They intervals throughout the day, using the Kjeldahl were mainly from his laboratory with a few from method. A portion of each collection was reserved Chas. D. Wood of the Maine Experiment Station. as part of a composite sample for the day. Nitro- In addition to the first 16 experiments conducted gen and the heat of combustion were determined prior to the 1897 report, the next 25 of the series on a portion of this composite and the remainder may have been completed before the 1899 report was preserved by adding formalin or thymol. was prepared. Possibly these 41 experiments, This became a part of the composite sample for together with 5 unpublished from the Maine the whole period of usually 3 to 4 days. The Experiment Station, made up the 46 experiments analysis of the total composite sample checked to which Atwater referred in the 1899 report.

15 TABLE 9.—Daily food intake in the experiments from which Atwater originally obtained the calorie-nitrogen ratio of 7.9 for urine

Respiration experiments Metabolism experiments Digestion experiments Food item 43 1 2 3 41 6 6 7 8 37 39 41

Qrams Grams Qrams Qrams Grams Qrams Grams Qrams Grams Grams Grams Grams 150 Beef, fried 121 121 96 96 120 100 169 150 121 100 170 Beef, dried _ _ __ _. _ 25 25 25 25 Ham deviled ""50' ""52' Eggs _ __ 95 54 141 95 107 52 144 103 ""98" '"iôr ""iöö' 850 Milk, whole (assumed raw) 1,000 500 660 ~'65Ô" 775 850 575 850 775 850 575 Cheese 75 75 Butter. . 35 35 20 45 35 75 15 35 34 75 15 35 Bread, brown 250 Bread white 150 450 45Ö Bread, rye _ _ _ 250 228 275 "325" 150 325 316 150 328 Crackers, milk 100 100 Oatmeal 40 6 Sugar - __ """2Ó" "~'4Ö' ""46" ""20' 35 50 45 40 38 50 45 40 Beans, baked 120 125 125 125 125 125 125 125 125 Potatoes, boiled in skins 150 150 270 100 Apples 85 125 200 200 Peaches 140 Pears, canned _ _ _ 210 150 300 150 150 300 150 Alcohol 72. 5 72. 5

Includes experiments 4P, 4A, 4B, 4C, and 4S. (See table 8.)

In the 25 additional published experiments in calories and in the levels of protein, fat, and carbo- this series conducted prior to 1900, the diet was hydrate. The urinary calorie-nitrogen ratio for modified somewhat as compared with the first 16. these experiments varied from 6.44 to 10.36. Both It consisted of beef, whole or skim milk, butter, extremes were within those observed for experi- bread, cereal breakfast foods, graham crackers, ments conducted prior to 1900; the average was ginger snaps, and sugar. The estimated nutrient 8.32, a little higher than for the preceding intake was similar to that of the preceding experi- experiments. ments except that the ascorbic acid content was Many other studies have been made in which lower, probably only between 10 and 20 milligrams data on urinary nitrogen and energy have been per day. The average calorie-nitrogen ratio for reported. To facilitate further study of this the 41 experiments, 7.88 (table 8), is not different problem, some of these are noted below. from that found for the first 16 alone, 7.86. Rubner {H8) determined the calorie-nitrogen The calorie-nitrogen ratio of the urine in these ratio in urine on a variety of mixed diets, reporting 41 experiments showed a wide variation with a an average ratio of 8.5. But a number of years range from 5.22 to 10.54. As the number of later in a paper with Thomas {151) he reported experiments under any one set of conditions was that the ratio was between 7 and 8, although he limited, it is scarcely feasible to conclude from this had found variations outside this range. Among series how different factors such as level of intake, other problems Rubner {H8) studied the influence extent of digestibility, type of diet, and degree of of level of fat, single foods, and periods of rapid activity influenced the calorie-nitrogen ratio of the growth on calorie-nitrogen ratio of the urine and urine. To the data in table 8 aheady mentioned, summarized the results as follows: we have added data selected or calculated from the rest of the 55 metabolism experiments completed Food Calories per Duration of after 1899, and data from a series of metabolism gramN experiment experiments, numbers 56-67 by Benedict and Days Milner {27), which was actually a continuation of Mother's milk^ • _ 12. 10 the earlier series of Atwater and Benedict. Bene- Cow's milk, infants 6.93 7 dict and Milner resumed the investigations of Cow's milk, adults ___ .______. 7.71 7 matter and energy in 1903. We have included Diet poor in fat _ _ _ 8. 57 2 Do ~ a 33 4 data from these studies for reference since copies Diet rich in fat _ _ 8.87 2 of the various publications in which the experi- Do __ 8.44 4 ments were reported are no longer readily available Boys' mixed diet- 6. 42 4 and they furnish much valuable basic data. Boys' mixed diet rich in fat _____ 7.50 4 Meat 7. 69 1 The diets of the experiments conducted in 1900 Potatoes 1 and later showed very wide variations in gross 7. 85

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O) 1 1X3 1 ^ (D .íií 1 T3 Ö 1 ' >-. d ' d Ö > '2 0 §^jf^c|.|5§8 ¿AiSüO¿>^5g^ 17 Eubner and Thomas {151) found the urinary of the food eaten. This is not surprising since calorie-nitrogen ratio for a subject on a diet solely less than a third of the gross calories from the of potatoes to be 9.04, 11.92, and 10.09 for the 1st, digestible protein is involved, and digestible 4th, and 6th days respectively—^ratios which were protein makes up only 10 to 25 percent of the much higher than Eubner had observed in earlier total calories in these diets. Consequently, an experiments except for the infant on mother's error introduced by the use of an average calorie milk. Sherman (l56) reported a series of metab- value per gram of either urinary nitrogen or net olism experiments on very simple diets of crackers absorbed nitrogen does not affect •greatly the and milk and in some cases butter. In one series calculated available energy of the whole diet. periods of restricted and liberal intakes were alter- For individual high-protein foods such as lean nated. Experimental periods of 3 to 5 days fol- meat and some defatted nut and legume products, lowed consecutively, two series for 12 days each urinary loss might be a much more significant and a third series for 20 days, to provide a better factor in determining available energy. If suitable basis for following and hiterpreting changes in the data were available not only for foods of high composition of the urine. There was no apparent nitrogen content but for all foods having some difference in the calorie-nitrogen ratios found for nonprotein nitrogen, and if data were available the periods on restricted and liberal intakes. The on the digestibility and utilization of the various range was 7.39-8.00. In general the ratio was nitrogenous compounds, a more accurate procedure somewhat lower than that found by Atwater and for calculating available energy could be developed. coworkers for subjects on mixed diets. Such data are not available and we are continuing Benedict made an extensive investigation of to use Atwater^s correction of 1.25 calories per nitrogen and energy losses in the urine under gram of available protein (nitrogen content 16 fasting conditions, reporting his results in two percent). pubhcations {25, 26), When body material is For purposes for which the calculation of urinary metabolized the calorie-nitrogen ratio appears to energy loss from nitrogen in the usual way is not be even more variable than that foimd for differ- satisfactory, attention is called to the work of ent kinds of mixed diets but the average ratio is Rubner {149) and of Benedict {25, pp. 490-492). higher. He reported ratios in the range of 8 to Benedict found less variability in the ratios of 10 for the first day of fasting, increasing with each calories to either carbon or organic matter than successive day until after several days some were in the ratio of calories to nitrogen. He found in the range of 14 to 18. closer relationship when he related the energy to Several investigations have been made in which carbon but in view of the difficulty in determining calories and nitrogen in the urine of children have carbon he suggested as a more feasible procedure, been reported, notably those of Macy {Illy 112). using the somewhat less constant calorie-organic Her studies provided data on a group of children matter ratio of the urine. The latter was largely ranging from 4 to 12 years of age over an extended proportional to the carbon content of the inline period of time. From the composition of the urine and far more readily determined. Benedict's reported the calorie-nitrogen ratio has been cal- suggestion for making the urinary energy deduc- culated for each child. The ratio does not appear tion on this basis rather than using the more to differ appreciably from that obtained by variable calorie-nitrogen ratio in estimating avail- Atwater for adults. Related problems have been able calories in foods should be given further studied by Folin {54) j Rubner {14^), Rubner and consideration. Heubner {150), and Tangl (i^O). In view of the wide variation observed for the Alcohol calorie-nitrogen ratio of the urine, the use of an average calorie value per gram of nitrogen may The perplexing subject of the energy value of be questioned. Data providing a measure of the alcohol has been investigated from time to time magnitude of the discrepancies when the avail- for more than 50 years. Investigations have able energy of the whole diet is calculated by the included such problems as the extent to which three procedures outlined on page 8 have been alcohol can spare protein for building or mainte- brought together in table 11. The experiments nance of body tissue, and the use of alcohol for selected represent the more extreme conditions on muscular activity, deposition of fat, and generation record as foUows: (1) Those in which the actual of heat for maintenance of body temperature. calorie-nitrogen ratio of the urine was considerably above or below the average; (2) those in which the Particularly controversial has been the question subject was in different states of N-balance; and of the body's use of alcohol for muscular work. (3) those in which the subjects had diets of widely The gross energy value of alcohol is 7.07 different composition with respect to proportions calories but its physiological energy value has of calories from fat, protein, and carbohydrate. been assessed variously by different groups of The data show that although the amount of investigators. Daniel, 1951 {45) suggested using energy lost in the urine is highly variable, on the about 5.0 calories per gram, since from animal whole it is small compared with the gross energy experiments and various biochemical studies it

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20 balance, the potential energy of food and unoxi- net income. Atwater and Benedict concluded dized excreta, the kinetic energy of heat given off, that the energy of alcohol oxidized was trans- and the external work performed. formed completely into kinetic energy and ap- Each subject had a rather simple diet consist- peared either as heat or as muscular work, or both. ing of such ordinary foods as meat, milk, bread, Atwater and Benedict made some deductions cereals, butter, sugar, and in some cases, coffee. concerning the protecting effect of alcohol on During the rest experiments the diet supplied about body material, based on the carbon, nitrogen, and 2,500 calories and during the work experiments, hydrogen balances of the subjects. From these about 3,900 calories. In the rest experiments the balances they estimated the daily gains and losses subject performed as little activity as possible in of body fat and protein, assuming that the glyco- addition to the necessary motions of dressing, un- gen stores for each individual at the beginning and dressing, handling of samples, recording of data, end of the experiment were the same. They and the daily setting up and taking down of his found some gains and some losses of body fat on cot. Most of the day was spent sitting, reading, either kind of diet but on the average there was or writing. In the work experiments he rode a sta- a gain. This gain was slightly larger when the tionary bicycle for a total of 8 hours a day. subjects were on the diets including alcohol than Alcohol was substituted for either carbohydrate when on the ordinary diets; 2.4 grams daily as or fat or a mixture of both in 13 experiments, in- compared with 1.1 grams of fat in comparable cluding rest and work experiments. About 72 experiments with and without alcohol. Storage grams (about 500 calories) were given in 6 small and loss of body protein also was calculated. Com- doses, 3 with meals and 3 at regular intervals parisons made between the ordinary and alcohol between meals. Thus it furnished about a fifth periods indicated that alcohol was slightly inferior of the calories during the rest experiments and to carbohydrate or fat in protecting body protein; between a seventh and an eighth of the calories that is, a larger average daily loss, 6.9 grams, of during the work experiments. body protein occurred in the alcohol periods than The data showed that alcohol had no practical the average loss, 3.5 grams per day, for the ordi- effect on digestibility except possibly in the case nary periods. of protein. The coefficient of apparent digesti- Loss of the energy of alcohol by radiation of bility of protein was a little larger in the experi- heat seemed to account for only a small proportion ments when the diet included alcohol than in of the calorie value. Atwater and Benedict found comparable experiments without alcohol, 93.7 that the radiation of heat from the body was only percent as compared with 92.6 percent. slightly greater with the alcohol diet than with The amounts of unoxidized alcohol given off by the ordinary diet, and amounted to not more than the kidneys, lungs, and skin were measured and 6 percent of the energy of alcohol. deducted from the amount ingested. The differ- Some of the results of the six groups of experi- ence was taken as the amount of alcohol oxidized ments (totaling 15 balances on 2 men) in which in the body. Previous research by another the alcohol and nonalcohol periods were more worker had indicated that alcohol was not ex- nearly comparable are shown in table 12. As the creted by way of the intestine even when con- protein intake within each group of comparable siderable quantities were taken. Therefore, no experiments with and without alcohol is nearly analysis of feces for alcohol was made. In these constant, these data indicate approximately the experiments only small amounts of unoxidized effect of alcohol on both the apparent digestibility alcohol (0.7 to 2.7, averaging 1.3 grams) were of protein and on the retention or loss of digested recovered. The authors concluded that not more protein. There was a small increase in apparent than about 2 percent would be given off unoxidized digestibility and also some increase in urinary when taken in amounts comparable to those in nitrogen excretion when the diets included alcohol. these experiments. They suggested using 98 The heats of combustion which Atwater and percent of the gross heat of combustion as the Benedict applied in experiments 9 and 10 to value of alcohol. changes in body protein and fat were 5.65 and 9.54 From these results Atwater and Benedict com- calories per gram, respectively. In their later pared the energy of the daily net income and the experiments they changed the figure for body fat outgo for subjects on diets with and without as they considered 9.4 calories per gram more alcohol. The net income was the energy of the nearly correct. The net effect of alcohol on gain material actually oxidized in the body, and was or loss of body protein and fat in terms of total determined by adjusting the available energy energy change is shown in column 13. 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lO l> 1> ft t>i CD c5 ci ci >.í^ a o Oi Oi ft M-S T-H tíft^ T3 tí ft •"tí^ ai 1 ÎQ CD ^ tí «D S bOÖ o o o tí ¡-f tí TJ O (1) ^o ^ tí ^^ 1 ft 1 1 !>. ;>,bûO a ;í-.TI «4-t <4-( T3 O faß bO (M "=. 03^'*-' o T3 o Ö o fí t>. M o^ 0"> >!> £. "S O tí ■s O) T3 -fJ 0*+H C^- § 0^ CO --^tH bß mixe 63.5 510 0 ithou i;i-Hio tí(lí(M(üSgo' ^ ^ 75 tí CO ft^^ S '-' «3 1=1 o Ö •§ w f;': d p: TI .2í TÍ4 co "^ g^tí^^^ g o 00 00 -" ft a> m« o o3r-H g^ t^ tí CD :tí ^ w '-5 23 A comparison of the experiments with and corresponding nonalcohol experiment. Under tne without alcohol (column 13) indicates that within conditions of these experiments Atwater and each group, when 72 grams of alcohol (509 calories) Benedict concluded that alcohol must have been replaced an approximate calorie equivalent of used by the body about as efñciently as the nutri- fat and/or carbohydrate, the calculated net gain ents from ordinary food it replaced. In the most or loss of energy value in the form of body tissue extreme case, alcohol calories were only about was sometimes a little larger and sometimes a four-fifths as well used as the food calories which little smaller than the change calculated for the alcohol replaced. These experiments do not comparable experiments when no alcohol was prove but suggest that under the conditions included. In these six groups of experiments comparable to those in these experiments much the calculated calorie change of body tissue varied from an additional gain of 83 calories to a of the energy of alcohol can be used m the body larger loss of 95 calories as compared with the for internal or muscular work.

PART III. DERIVATION OF CURRENT CALORIE FACTORS

Since Atwater first proposed his individual food laysen {SO) compared utilization of protem and group factors and his general factors for estimating dry matter in wheat and rye brans by man with the fuel value of mixed diets as a whole {17) ^ utilization by sheep and swine. Later Crampton enough data for a number of foods have accumu- and others {^S) compared man^s use of several lated to make possible some revisions and addi- grain products with that of rats, sheep, and swme. tions. For other foods more data are urgently However, there is insufíicient evidence at present needed. for concluding that digestibility of nutrients by Prior to 1947 the Bureau of Human Nutrition experimental animals can be used to predict that and Home Economics had summarized the of man. If a relationship could be established, available information on digestibility by man of research in this field could proceed more economi- bread made from wheat of three levels of extrac- cally and more rapidly. tion and had compiled preliminary material for The energy factors shown in table 13 do not potatoes. Since then, study of the scientific rest on equally rehable information. The number literature has been continued, permitting the of subjects for different foods varied considerably. addition of coefficients of digestibility for many In general, no information was available on the more items. Data from the digestibility studies possible departure of the test diet from the previ- reviewed are given in appendix tables 23 and 24. ous dietary pattern. Lack of uniformity was The resulting summary of data on human digesti- observed in the experimental procedures used, bility and heat of combustion needed for deriving including lengths of the preliminary and experi- specific calorie values of individual items of food mental periods, choice of marker, and the relative or of small food groups is given in table 13. proportion of the diet furnished by the test food. Where further information was lacking, Atwater's The foods tested, expecially in the early digestion data were taken from the revised figures for col- experiments, were not always adequately de- umn F in table 10 of his report cited above and scribed, nor was the chemical composition of the reproduced as table 7, page 10. The figures in sample always reported. In some cases, reason- columns 4, 7, and 10 are the specific factors to be able assumptions could be made as to the identity applied to the grams of protein (nitrogenous of the samples. For a few foods neither descriptive material), fat (usually ether extract), and carbo- nor composition data were reported by the hydrate (determined by differences) in the food investigators, and energy factors derived from to obtain the physiological energy value. digestibility data in those experiments may be Before discussing the derivation of the specific shown by future work to need considerable calorie factors shown in table 13, a few general revision. Grain products of various degrees of observations should be made regarding the basis milling as described some 50 years ago have of the data. presented particularly knotty problems. Although The basis for the coefficients of digestibility in table 13 could have been broadened greatly, if the the products were identified by extraction and large volume of work with experimental animals other recognized milling terms, composition data in the literature had been included. Some work in addition were necessary to classify them in has been done to compare digestibilities of man terms of the most nearly comparable products on and experimental animals. Brierem and Nico- the market today.

24 TABLE 13.—Data used for calculating energy values of foods or food groups by the Atwater system

Protein Fat Carbohydrate

I'actor Factor to be to be Food or food group Coefla- Heat of Coem- Coeffi- applied Heat of applied Heat of cient of combus- to in- cient of combus- to in- cient of digesti- tion loss digesti- digesti- combus- 1.252 gested tion gested tion bility nutri- bility nutri- bility ents ents

(1) (2) (3) (4) (5) (6) (7) m (9)

Eggs, Meat products, Milk products: Pet. Cal./(jm. Cal.lgm. Pd. Cal./gm. Cal.jgm. Pet. Cal.jqm. Eggs 97 4. 50 4. 36 95 9. 50 9.02 98 3. 75 Gelatin 97 4. 02 3.90 95 9.50 9.02 Glycogen 98 4. 19 Meat, fish 97 4. 40 4.27 95 9. 50 9.02 Milk, milk products 97 4. 40 4.27 95 9.25 8.79 "98' 3.'96" Eats, separated: Butter 97 4. 40 4.27 95 9.25 8.79 98 3.95 Other animal fats 95 9. 50 9.02 Margarine, vegetable '97" 4 4Ö' '4.'27' 95 9.30 8.84 3.'95" Other vegetable fats and oils 95 9. 30 8.84 Fruits : All (except lemons, limes) 85 3.95 3.36 90 9.30 8.37 90 4.00 Lemons 85 3. 95 3. 36 90 9. 30 8.37 98 2. 75 Limes 85 3.95 3.36 90 9.30 8.37 98 2.75 Grain products: Barley, pearled 78 4. 55 3.55 90 9. 30 8. 37 94 4.20 Buckwheat flour, dark 74 4. 55 3.37 90 9.30 8.37 90 20 Buckwheat flour, light 78 4. 55 3. 55 90 9. 30 8. 37 94 20 Cornmeal, whole ground 60 4. 55 2.73 90 9.30 8.37 96 20 Cornmeal, degermed 76 4. 55 3. 46 90 9.30 8. 37 99 20 Dextrin 98 11 Macaroni, spaghetti 86 4. 55 3. 91 90 9.30 8. 37 98 20 Oatmeal, roUed oats 76 4. 55 3. 46 90 9. 30 8. 37 98 20 Rice, brown 75 4. 55 3.41 90 9.30 8.37 98 4.20 Rice, white or polished 84 4. 55 3.82 90 9.30 8. 37 99 20 Rye flour, dark 65 4. 55 2.96 90 8. 37 90 20 Rye flour, whole grain 67 4. 55 3.05 90 8.37 92 20 Rye flour, medium 71 4. 55 3. 23 90 8. 37 95 20 Rye flour, light 75 4.55 3.41 90 8. 37 97 20 Sorghum (kaoliang) ^ whole or nearly whole meal__ 20 4. 55 .91 90 8. 37 96 20 Wheat, 97-100 percent extraction 79 4.55 3. 59 90 9.30 8. 37 90 20 Wheat, 85-93 percent extraction 83 4. 55 3.78 90 9. 30 8. 37 94 4.20 Wheat, 70-74 percent extraction 4. 55 4.05 90 9.30 8.37 98 4.20 Wheat, flaked, puffed, rolled, shredded, whole meal 79 4. 55 3. 59 90 9.30 8. 37 90 4.20 Wheat bran (100 percent) 40 4. 55 1. 82 90 9.30 8.37 56 4.20 Other cereals, refined 85 4. 55 3. 87 90 9. 30 8. 37 4.20 Wild rice 78 4. 55 3. 55 90 9.30 8.37 4. 20 Legumes; Nuts: Mature dry beans, cowpeas, peas, other legumes; nuts 78 4.45 3.47 90 9.30 8.37 97 4.20 Immature lima beans, cowpeas, peas, other legumes 78 4.45 3.47 90 9. 30 8. 37 97 4.20 Soybeans, dry; soy flour, flakes, grits 78 4. 45 3.47 90 9.30 8.37 97 4.20 Sugars : Cane or beet sugar (sucrose) 3. 95 3.75 Glucose Vegetables : 70 3.75 2. 62 90 30 .37 85 4. 10 Mushrooms 96 4.20 Potatoes and starchy roots 74 3.75 2. 78 90 30 .37 74 3. 75 2. 78 90 30 , 37 96 4.00 Other underground crops * 85 4.20 Other vegetables 65 3.75 2. 44 90 30 37 Miscellaneous foods: Alcohol 5 42 4. 35 1. 83 90 30 37 32 4. 16 Chocolate, cocoa 98 2. 45 Vinegar 80 4.20 Yeast_ ' 80 3.75 3.00 '90' '30' "37'

heart, kidney, 1 In a few cases values in columns 4, 7, and 10 are slightly 3 Carbohydrate factor, 3.87 for brain, liver; 4.11 for tongue and shellfish. different from those shown in table 7, column F, revised, parsnips, because of different methods of rounding figures. 4 Vegetables such as beets, carrots, onions, 2 The correction, 1.25 calories, has been subtracted from radishes the heat of combustion. This gives values applicable to 5 Coefficient of digestibility, 98 percent; heat of com- grams of digested protein and identical with Atwater's bustion, 7.07 calories per gram; factor to apply to mgestea factors per gram of available protein. alcohol, 6.93 calories per gram. 25 Physiological Fuel Values of Foods of Animal Origin

For determining physiological fuel values of energy factor used in this publication, 3.68 calories foods of animal origin, Atwater's factors for the dif- per gram, was obtained by applying the coefficient ferent categories are still being used with only slight of digestibility, 98 percent, to 3.75, the heat of changes. His coefficient of digestibility of 97 combustion of glucose. Perhaps this figure is too percent for the protein of meat, fish, eggs, and low for simple sugars which require no digestion. dairy products has been used without change in Appreciable amounts of glucose and glycogen this pubUcation (see table 7). have been found in tissue of brains, heart, and Many items of animal origin contain small glandular organs, the relative amounts varying amounts of carbohydrate to which Atwater according to metabolic conditions at the time of applied the energy factor 3.82 calories per gram. slaughter and conditions of storage. For heat of He obtained this using 3.90 calories as heat of combustion, 3.95 calories per gram, a figure inter- combustion and a coefficient of digestibility of 98 mediate between the heats of combustion of percent. Some small revisions in this factor are glucose and glycogen, has therefore been selected, indicated in view of current information on the resulting in a physiological energy factor of 3.87 form of carbohydrate predominating in the dif- calories per gram. ferent kinds of foods of animal origin. These Analyses have shown glycogen to be the main revisions, which are very minor, are noted in the carbohydrate constituent of tongue and some following paragraph. kinds of shellfish. Hence, to derive an appropriate For the carbohydrate of milk and milk products, energy factor, we applied the coefficient of digesti- we have used for the physiological energy factor, bility, 98 percent, to 4.19, the heat of combustion 3.87 calories per gram. This is based on the heat of glycogen, and the resultant factor was 4.11 of combustion for lactose, 3.95 calories per gram, calories per gram. and Atwater's coefficient of digestibility, 98 For animal fats we have used Atwater's energy percent. factors, 8.79 calories per gram for fats in dairy Eggs contain a small amount of carbohydrate, products and 9.02 for fats from other animal chiefly glucose, bound in a large complex. The sources.

Physiological Fuel Values of Plant Products

Separated fats of plant origin are important mainly from adding data from a comprehensive items today but were practically imknown 50 review of digestibility studies reported since 1875. years ago. For them we have used the digesti- For a few foods the revisions result from changes bility coefficient, 95 percent, that Atwater used in the heat of combustion factors used. More for butter and other animal fats. For the heat of specific energy factors, together with the average combustion of fat in plant products, whether or coefficients of digestibility and heats of combustion not separated, we have continued the use of from which they were derived, are presented in Atwater's factor, 9.3 calories per gram. table 13. The basis for the differences in these Margarine as manufactured in the United figures as compared with Atwater's factors for States of America may be made of either animal food groups is discussed in the remainder of this or vegetable fats, and a few States have laws section. In some instances the values may prove requiring a specified high proportion of animal to need further revision as the result of future fats. However, as most margarine in this country research, but we believe them to be better ap- is made with vegetable oils, the factor 8.84 calories proximations for individual foods than either the per gram for fat in margarine shown in table 13 general, overall factors or the food group factors was based on heat of combustion of 9.3 calories that were developed in 1899. The basic data on per gram and a coefficient of digestibility of 95 digestibility from which the factors were obtained percent. Margarine of either type and butter have been compiled in table form (appendix contain small amounts of protein and carbo- table 23). hydrate carried over from the milk in which the This compilation is not entirely complete for fats were blended or chxu-ned. The calorie factors studies reported in foreign languages, but we for protein and carbohydrate of milk were used beheve it covers the bulk of early and recent for those constituents of margarine. research m which apparent digestibility of the test For fat as it occurs in cereals and other plant food was measured. Articles in which apparent sources Atwater assumed the apparent digesti- digestibihty was not reported or could not be bility to be 90 percent and we have continued this calculated for the test food alone were not in- practice. The energy factor for fat in plant foods cluded. By this criterion, digestion experiments is therefore assumed to be 8.37 calories per gram. such as those of F. Erismann (52) were excluded. The revisions we have made in the Atwater His coefficient of digestibihty for protein has been factors for the physiological fuel values of protein quoted by various authors in early pubhcations as and carbohydrate of plant products have resulted applying to peas, but a translation of the original 26 article shows that the coefEcient was applied to second clear, red dog, and shorts, indicating that bread made of 50 percent pea meal and 50 percent It may have been somewhat more than 85 percent rye flom^ without adequate basis for calculating the of the kernel. For comparison, the average mifl- digestibility of the pea meal alone. Included in mg yields from several commercial milHngs of the compilation are several experiments which cleaned wheat reported in 1941 by Sherwood and contribute useful information although for various others {160) have been included here as follows: reasons they have been excluded from the data used for obtaining average coefficients. Milled fraction: yield The derivation of the energy factors in table 13 Patent flour ^3 Q is discussed in the following paragraphs by food First clear flour 7Q groups since foods within a group have certain Second clear flour 4 5 Red dog flour ..._ ¿0 characteristics and problems in common. Where Germ '_ * 2 no mention is made of the derivation of factors, Shorts _ 12*3 Atwater's data considered most appHcable to the Bran V\V.V__ ao particidar item or small food group have been used. If it could be assumed that the sum total of the fractions comprising the entire-wheat flour of the Products of wheat early experiments was comparable to the fractions reported by Sherwood, theoretically the yield of By far the largest proportion of the digestion entire-wheat flour would have been close to 91 experiments reported have been concerned mth percent. UsuaUy the entire-wheat floiu* was re- foods of the cereal group. Of the cereal foods ferred to as being of about 85-percent extraction. wheat has been studied in most detail. Probably this was a little low. Woods and Mer- Flours rill {194) stated that 100 pounds of cleaned No. 1 wheat would make 85 to 88 pounds of entire-wheat Digestibility of wheat flour was studied first by flour, that the large mifls gave rather larger yields Eubner and other European scientists during the than small mills, and that a starchy wheat yielded latter part of the 19th century. As milling 1 to 3 pounds more than a hard wheat. They practices and the terms used have changed over also stated that the ash content of the entire-wheat the years, we encountered problems in deciding flour was about half that of the whole-wheat flour. how to combine and group the large volume of Suyder {164, lp6, 168) also conducted experi- data on the digestibility of wheat flours. Wheat ments in that period and used entire-wheat flours, flours milled commercially and experimentally but the indications are that the flours he used have been studied extensively since 1900, par- were of somewhat longer extraction than those ticularly in the United States and in Great Britain. described by Woods and MerriU. The flours of Por a great many of these flour samples, enough longer extraction were obtained by removal of information is available so that the flours can be part of the coarser brau by screening and the arranged in three groups according to degree of inclusion of fine bran, shorts, and germ. The extraction from the kernel. These three groups amount of coarse bran removed varied from a were described by United States scientists in the small proportion to over half the total amount early part of the 20th century as graham, entire present. Data he reported showed that the ash wheat, and as straight or standard patent. Not content of the entire-wheat samples ranged from all the terms used then still apply but the data are 51 to 92 percent of that in the wheats from which usable. they were milled. In view of this kind of infor- Graham was essentially whole-wheat meal, but mation it is likely that entire-wheat flour repre- may have had a very small amount of coarse sented about 90 percent of the cleaned wheat. material removed. The straight and standard The latter figure was also arrived at independently patent flour group contained the first and second by a milling expert in the United States Depart- patent flours and the first clear flour and made up ment of Agriculture who estimated the probable about 70 to 72 percent of the wheat kernel, which extractions of a number of samples of entire-wheat is in line with modern-day yields of straight flour from their ash contents in relation to the grade flour. Data on the composition of the ash content of the whole-wheat from which each straight patent flours used in the early experiments was milled. when reported also indicated that from the stand- Since such estimates may be more or less in point of proximate constituents the straight error, and since the information on the muling patent flours were similar to those produced in and composition of the fiours suggests that the recent years. In some instances the standard entire-wheat flour was not always of uniform patent was blended with small amounts of the extraction, we have considered it preferable in low-grade flours, second clear and red dog. this publication to assume that the data applied to More variation existed in the flours included in flours within the range of 85- to 93-percent extrac- those of the intermediate extraction. The so- tion. Likewise for flours designated as standard called entire-wheat flom* as described by Woods patent we have assumed that the data applied to and Merrill {194) included patent, first clear. flours of 70- to 74-percent extraction. With re- 27 gard to the whole-wheat or graham flours used in The wheat samples used in the digestibility the early studies, it has been assumed that flour studies were largely hard wheats, both sprmg so designated may have been of from 97- to 100- and winter varieties; a few soft wheats were percent extraction, since there was some evidence included. Data on proximate composition were that a small amount of the outer portion of the available for the whole-wheat flours used in 18 kernel may have been removed. digestibility trials, for the flours of intermediate The average coefficients of digestibility of pro- extraction in 22 trials, and for the straight and tein and of carbohydrate for wheat flours of these patent flours in 28 trials. Average values for three extraction ranges are based on more than the flours of known composition are shown in the 70 digestibility trials on whole-wheat and near first column of table 14. Within each of the three whole wheat flours, more than 50 trials on wheats groups there was much variation. The protein of interniediate extractions, and over 100 digesti- content of the whole-wheat samples, for example, bility trials on straight and patent flours. The ranged from 8.5 to more than 15 percent, the average coefficients of digestibility are shown in majority containing over 12 percent. At present, table 14. The variation in digestibility found for data are inadequate to determine to what extent the protein of wheat was much greater than that variation observed in digestibihty within groups for the carbohydrate, and there was greater varia- and between groups may have been due to differ- tion in the digestibility of longer extraction flours ences in protein and carbohydrate content of the than for refined flours of shorter extraction. flours.

TABLE 14.—Energy values oj wheat Hours calculated by use of specific energy factors for protein, fat^ and carbohydrate

Energy fac- tors to be Available Coefficient of Energy value applied to energy of food Type of flour Composition ' digestibility of available ingested using specific nutrient nutrients factors (col. 2 Ccol. 3 X col. 4) X col. 5) (1) (2) (3) (4) (5) (6)

Essentially whole wheat ^ (97-100 percent extraction) : Percent Percent CaL/gm. Cal.lgm. Cal.jlOO gm. Protein (N X 5.83) _._ 12.6 79 34.55 3.59 45.2 Fat _ __ 1.9 ' 90 9.30 8.37 Carbohydrate by difference 71.8 90 4.20 3.78 271.4

Total 332.5 Intermedíate extraction (85-93 percent) : ^ Protein (N X 5.7) 12. 0 83 3 4. 55 3.78 45.4 Fat 1.8 4 90 9. 30 8.37 15.1 Carbohydrate by difference. 73.0 94 4.20 3.95 288.4 Total 348. 9 Patent ^ (70-74 percent extraction) : Protein (N X 5.7) __ 11.7 89 34.55 4.05 47.4 Fat _-. _ 1.3 < 90 9.30 8. 37 10.9 Carbohydrate by difference 74. 5 98 4. 20 4. 12 306. 9 Total. 365. 2

^ Composition data are calculated to a 12-percent 3 1.25 calories have been deducted from the heat of moisture basis. combustion of 1 gram of protein to correct for loss of 2 The ash content found for the wheat flours are 1.7 incompletely metabolized products in the urine. percent for essentially whole wheat, 1.2 percent for wheat * Assumed coefficient of apparent digestibüity for fat in of intermediate extraction, and 0.5 percent for patent plant products, 90 percent, used because actual data for- flour. wheat were unsatisfactory.

The average digestibility of the protein and nous portion of flours of different extraction rates. of the carbohydrate for any one type of flour of The relative proportions of protein and nonprotein known chemical composition showed differences nitrogen compounds and the composition of the of less than 1 percent from average coejEcients of di- protein fraction itself are each known to vary. gestibility obtained by using data from all of These changes would be expected to affect the the samples of that type. The coeJQBcients based heat of combustion and hence the energy factors on all the samples within the group, therefore, also. However, in preparing table 14, no attempt were used for deriving the energy factors shown !^^s made to adjust the heat of combustion data in table 14. It is unlikely that the heat of com- for differences in the heat values of the protein or bustion value would be the same for the nitroge- fat mixtures in the flours of different extractions. 28 Energy values for flours at each of the three remamed to be distributed among such factors as extractions have been worked out from the com- level of protein intake, level and nature of carbo- position data of the known samples. The results, hydrate, length of experimental period, the varia- shown in the last column of table 14, are con- tion characteristic of each subject, and fineness of sidered suitable for flours of the extractions and grind of the flour. compositions specified. From time to time calorie values for flours of TABLE 15.—Apparent digestibility and physiological other extractions are needed. To estimate co- fuel value of wheat flours efficients of digestibility for protein and carbo- hydrate in such flours, the digestibility data Coefficient of digesti- estimated at the three extraction rates, 100, 90, bility Specific energy factor and 70 percent, for the wheat flours just discussed Perci^nf Evtraptinn were used. This was done inasmuch as the few Protein Carbohy- Carbohy- scattered digestion experiments reported on flours drate ProteiQ drate of other specified extractions of wheat were so Percent Percent Cal/gm. Cal./gm. varied in conditions and methods that the results 100 79 90 3. 59 3. 78 were not usable for this purpose. The relation- 95 (81) (92) 3. 69 3. 8a ship between the percent extraction and coefficient 90- - 83 94 3.78 3.95 of digestibility of wheat can be expressed in the 85 (85) (96) 3. 87 4.03 80 (86) (97) 3. 91 4.07 form of the equation y=a-\-bx+cx^, where a:=per- 75 (88) ' (98) 4.00 4. 10 cent extraction and ?/= coefficient of digestibility. 70 89 98 4. 05 4. 12 By the method of least squares the constants for this equation, fitting the three points based on 1 97.5 by calculation, from equation, page 29. average digestibihty data for wheat of 100-, 90-, and 70-percent extraction, were as follows for^ protein and carbohydrate: Since 1945, when the relationship between coefficient of digestibility and degree of extraction were worked out rather hastily for wheat of 100-^ Value or constant 90-, and 70-percent extractions, some additional Equation constant data have been located in the literature and others Protein Carbohydrate have become available as the result of more recent research. The inclusion of these additional a - 0.890 0. 700 values did not warrant any change in the coef- h . 00233 . 00867 ficients of digestibility published earlier (55, 118)^ c -. 0000333 —. 0000667 and we have continued to use them. Methods of determining energy values used in Great Britain.—McCance and his associates have Digestibility coefficients (y) for other extraction given special attention to assessing the energy percentages (x) were computed by solving the values of cereals {102, 104, 108). They differ- equation. entiated between available and physiological From this equation, coefficients of digestibility calories and as both procedures differ from the of protein and carbohydrate were calculated for one used in this country and as certain of the flours of 95-, 85-j 80-, and 75-percent extraction. terms have different meanings we include here a The values found are shown in table 15. Addi- brief discussion of their work—particularly as it tional intervening points may be determined from relates to wheat. the equation or read from a curve. For conven- The consideration given carbohydrate has ience the energy factors to apply to the protein been an important difference between the systems and carbohydrate in wheat flours of the specified for estimating energy used by English and extractions are also included in table 15. American scientists. Data on carbohydrate in Degree of extraction has been accepted here as British tables of food composition are based on the most important influence on digestibility of ^^available carbohydrate,'' which includes sugars, wheat flour. To test this assumption an estinaate starches, and dextrins—carbohydrates assumed to was made of the extent to which rate of extraction be fully utilized by the body, but exclude as un- was associated with coefficients of digestibility. available, fiber and nonfermentable sugars or The relationship of these two, based on those pentoses. The analytical determination of avail- subjects for whom data were available at each of able carbohydrate has been discussed by McCance three extraction rates, was found to be represented and Lawrence {103). by an equation of the form y=a-\-bx-\-cx^j where Available calories as calculated by McCance are the extraction rate is the independent variable. the sum of the gross calories in the available B^, the variance, was 44 percent, showing that carbohydrate fraction of the food, plus the almost half of the variation in the coefficient of calories from fat after deduction for fecal lipids, digestibility was associated with variation in plus the calories from protein after deduction for extraction. This indicates that the assumption fecal and urinary losses of nitrogenous matter, was warranted since 56 percent of the variation In principle this procedure is similar to that used 29 in this country but the method for determining protein present with a deduction for urinary l<^ss available calories from carbohydrate is different; (4.35Xgrams of protein content in the wheat) also there are some differences in the actual Data reported by McCance and Walsham irom calorie factors selected for protein and fat. this study for gross, available, and physiological calories for the two samples of whole-wheat flour To illustrate how the calorie factors for the (15 percent moisture) were as follows: calculation of available calories are obtained, data are presented here from a study of McCance Canadian English and Walsham {lOJj). Digestion and utilization of Type of data wheat calories of two samples of whole-wheat flour, one wheat made from a low-protein English wheat and the Gross calories: Calories Calories other from a high-protein Canadian wheat were Fnnr! Cbomb) - - 372 350 determined for adult subjects. The calorie factors Fecal (bomb) -45 -40 for protein were found by applying the coefficients Urinary loss (LSXnet absorbed of apparent digestibility of protein found in these N^ -17 -8 digestion experiments to the factor 4.35 calories Available calories (from above) 310 302 per gram (5.65 less 1.3 calories per gram for urinary Available calories calculated by loss) used by Sherman {158) for the heat of com- A/TpCancp Drocedure 299 304 Physiological calories calculated by bustion of protein in a mixed diet. The apparent 320 digestibility of protein was found from the experi- A/rp(~î*iTirp TiTOCpdure - 320 ment to be 84.9 percent for the Canadian flour and 74.2 percent for the English flour. The calorie factor for fat was obtained by apply- Additional calculations of energy values.— ing 58 percent, the coefficient of apparent digesti- Using data from the same study, McCance and bility found for fat, to 9.45 calories the heat of Walsham also made two additional energy cal- combustion per gram of fat in a mixed diet {158). culations—one attributed to the Atwater pro- From these experimental data the calorie factors cedure and one in which energy factors for wheat to be applied to analytical data on the content used by Food and Agriculture Organization of protein and fat to obtain the calories from these were applied. We have not included results for nutrients in the two samples of flour were thus these two calculations for two reasons. The found to be 3.65 and 5.5 calories per gram, application of the general calorie factors for pro- respectively, for the Canadian and 3.21 and b.t> tein, fat, and carbohydrate of a mixed diet to a calories per gram for the English wheat flours. specific food is not a procedure used by Atwater. Calories from carbohydrates were obtained by Moreover, McCance and Walsham do not report applying the gross calorie factor for starch, 4.2, values for ash content and thus it is not possible to data on content of '^available carbohydrate^' to determine the total carbohydrate (by difference), expressed as starch for each wheat. a value needed to use the Atwater procedure Physiological calories as calculated by McCance correctly. When assumed figures for ash suggested include only the gross calories from those fractions by the authors were used, gross calories calculated of the nutrients which definitely may be con- from composition were observed to differ from sidered usefully available. Provision is made for bomb determinations by 15 calories per 100 grams excluding urinary calories, a loss resulting from in the case of Canadian wheat and 24 calories per incomplete combustion of protein, but no deduc- 100 grams in the case of English wheat. In tion is made for nitrogenous matter in feces; like- view of the close agreement previously reported wise no deduction is made for fecal fat. The (p. 6) between calculated values for gross calories fraction of the carbohydrate measured is con- and bomb calorimeter determinations, the dis- sidered completely available. It is treated in the crepancies of 4 percent for the Canadian and 7 same way for determining physiological calories percent for the English wheat seem too large to as in the determination of available calories—the warrant the use of these assumed figures for a fraction of questionable value as a source of energy comparison between the two methods of calcula- is excluded and a gross heat value is used with the tion. data on available carbohydrate content. For use We have not located any reports in the literature in food tables physiological calories are the values in which adequate data are given for evaluating McCance considers most suitable {102, 104y 108) j the two methods of assessing available calories because, as he has pointed out {107), it is unusual in foods—the McCance procedure outlined above to make allowance for losses in the feces in pre- and the Atwater procedure as we use it. For a senting data on composition of foods. correct appraisal of the two methods by means of Physiological calories based on data from the digestion experiments, the following data are experiment with the two whole-wheat floinrs were essential: (1) Chemical composition of the food calculated to be the sum of the calories from samples, which should include moisture content, carbohydrate obtained in the same way as for nitrogen compounds, fat, ash, carbohydrate by available calories above, plus the gross calories difference, and available carbohydrate (starch from fat (9.4Xgrams of fat in the wheat sample) and sugar); (2) bomb calorimeter determinations present in the food, plus the gross calories from of the foods and excreta. Such an evaluation, if 30 made for other types of food as well as wheat, 16 experiments. These coefficients were applied would provide very useful information. to the heats of combustion of protein (nitrogenous matter) and carbohydrate of wheat, and the energy Alimentary pastes; other flour mixtures factors obtained for the two nutrients after cus- Macaroni and other alimentary pastes usually tomary deduction for urinary nitrop-en loss were are made Avith semolina or durum flour as the 1.82 and 2.35. principal ingredient. This type of wheat has characteristics different from wheats used for Wheat breakfast foods preparing wheat flours for bakers and homemakers. Foods in this group have been studied in some Digestion experiments were carried out in 1905 detail in digestion experiments, but as the experi- by Snyder (168) and at an earlier date by several mental diets were low in protein the apparent European scientists to determine the digestibility digestibility as determined may have been too of macaroni and other kinds of alimentary pastes. low. Hence, rather than use these data in esti- Only in the study reported by Snyder was the mating digestibility, we used the coefficients of flour used in making the pastes described in any digestibility of whole-wheat flour (table 13) to detail. In this latter study the flour milled from obtain tentative estimates for whole-wheat meals durum wheat represented a somewhat larger and other whole-wheat cereals. Likewise for portion of the kernel and was more granular in farina and other breakfast foods made from the appearance than the patent flour used for bread endosperm we used the coefficients of digestibility making purposes. The average coefficients of of patent flour. These factors would result in digestibility found for macaroni, 86 percent for some overestimation of energy values for foods protein and 98 percent for carbohydrate, seemed subjected to special processing that reduces reasonable in view of other studies indicating that utilization of any of the organic nutrients and both degree of extraction and coarseness of grind possibly for meals of a coarser grind than that of affected the apparent digestibility, particularly of wheat flour. For breakfast foods that are mix- the protein, of flours. tures, we derived weighted energy factors if we The specific energy factors for protein and car- knew the kind and approximate proportions of bohydrate calculated by use of these coeiBcients of ingredients. _; ! \:^\Mm ..^ÉúlSi^MM digestibility and the heats of combustion of wheat flours were 3.91 and 4.12, respectively. The factors are considered applicable to the various ^Productslo^Srain^other thanlwheat^ ahmentary pastes made from flour and water. Digestibility of those containing eggs or milk might The digestibility and physiological fuel values of be somewhat different, but as only small amounts corn, oat, rice, and rye products have been studied of these optional ingredients are present separate less than wheat but more than most of the remain- factors are not proposed. ing grains. The digestibility of some other products in which Although information on the various cereals is flour is the main ingredient has been studied also. not strictly comparable, on the whole it indicates Deuel published results found for a variety of that differences in digestibility may be expected baked products including yeast breads, baking among grains and that neither the fiber content powder biscuits, cakes, cookies, crackers, and nor the level of protein intake alone appears to be others (45). The coefficient of digestibility of adequate basis to explain differences observed protein ranged from 85 to 94 percent and that for among cereals when fed to human subjects. carbohydrate from 97 to 99 percent. Spriggs and Weir (172) found the digestibility For flour mixtures that vary considerably with of the protein in a mixed diet containing bread respect to ingredients, such as cookies, energy made with white flour to be 91 percent, but when factors were calculated for each product, weight- only a third of the flour was replaced successively ing the energy factors of each ingredient in propor- by oatmeal, barley flour, fine sifted corn flour or tion to the amounts present in the product. rice flour the digestibility was 87.6, 81.5, 86.7, This procedure is explained in more detail on and 89.7 percent, respectively. Jones and Water- page 42. man {77) observed significant differences in the extent to which proteins may be digested in vitro Bran by pepsin and trypsin. They found that arachin, Differences in apparent digestibility between casein, and cooked phaseolin were 48, 61, and 58 whole-grain flours and those of short extraction percent digested and suggested that the order in suggested that bran might have a low coefficient which the amino acids were united to form the of digestibility. Some investigations have been proteins might be responsible for the incomplete undertaken to determine the digestibility of bran digestion; some linkages are more resistant than alone, and while the results were variable, the co- others to the hydrolytic action of digestive efficients were in every case very low. The aver- enzymes. age apparent digestibility found for the protein of Other workers studying the physiological avail- bran was 40 percent based on 14 digestion experi- ability of purified proteins have observed mde ments, and for carbohydrate, 56 percent based on differences in the proportions of a given amino

305774—55- 31 acid in the feces of experimental animals, depend- was close to 60 percent for protein and 96 percent ing on the protein fed. These and other studies for carbohydrate. These values are in line witn indicate that among the various kinds of cereals digestibility coefíicients for field corn (pressure- considerable difference in digestibility and physi- cooked) and for hulled corn (hominy), which, ological fuel values may be expected. Digestibil- judging by their fat and fiber content, must have ity data from the literature for the various kinds contained the germ and more of the branny por- of cereals have been summarized separately. The tion than degermed corn products. Degermed average coefficients of digestibility and the number cornmeal prepared as mush or as cornbread has of experiments on which each was based are shown been used in several studies. Average coefficients in table 16. As more research becomes available based on 21 digestibility trials were found to be these data will no doubt need revision. Data on 76 percent for protein and 99 percent for carbo- wheat have been included in the table for ease in hydrate. Hence, the energy factors suggested and used here for protein and carbohydrate m comparison. whole grain corn products are 2.73 and 4.03 calories per gram, and in degermed corn products, TABLE 16.—Coeßcients of apparent digestibility for 3.46 and 4.16. grain products Data on apparent digestibdity of frozen raw cornmeal and toasted corn breakfast products also Protein Carbohydrate were found in the hterature or could be calculated from the information reported by the authors. Grain Product Coeffi- Experi- Coeffi- Experi- They have been recorded in appendix, table 23, cient of di- cient of di- ments gestibility ments gestibility for reference but for various reasons were not used in assessing the energy value of corn products.

Cornmeal, whole- Percent Number Percent Number ground, bolted 60 3 96 3 Oatmeal Cornmeal, degermed. 76 21 99 21 Oatmeal, rolled oats 76 48 98 24 Several studies have been made of oat products, Kice, brown 75 22 98 22 mainly oatmeal or rolled oats, which were either Rice, white or milled.-. 84 119 99 119 cooked and used as a porridge or baked as oat "Rye flour: cakes. Also recorded in this appendix table but Dark 65 0) 90 AVhole-grain 67 0) 92 (0 not used in obtaining average digestibility figures Medium 71 0) 95 (0 were a few experiments on ready-to-eat cereals. Light 75 Q) 97 (0 Based on 48 digestibility trials, the average Wheat flour: coefficient of digestibility for protein was found to Essentially whole wheat, 97 - 100 be 76 percent and that for carbohydrate, based on percent extrac- 24 trials, 98 percent. As was the case with most tion 79 72 90 72 of the cereals there was more variation in the Intermediate, 85- coefficients of digestibility for protein than for 93 percent ex- tion 83 53 94 53 carbohydrate. Using the average coefficients of Straight or patent, digestibility, the energ}^ factors for protein and 70 - 74 percent carbohydrate are 3.46 and 4.12 calories per gram, extraction 104 104 respectively. In most cereals the quantity of fat present is so 1 Coefficients of digestibility for rye flours were derived small that the use of Atwater's assumed digesti- less directly as explained on pages 33 and 34. Therefore, the number of experiments is not indicated. bility coefficient of 90 percent for fat in plant foods introduces very little error in the total energy value of the food. Oatmeal, which con- Cornmeal tains 7 to 8 percent fat on an average, has more The cornmeals studied have been of two general fat than most cereals and its digestibility is of types, whole meal, sifted through a 16-mesh more significance. In 28 experiments in which sieve which may have removed a small amount of the digestibilit}^ of fat in oatmeal has been reported the bran, and degermed cornmeal which probably or could be calculated from data given, the results had most of the bran, as well as the germ, re- have varied from 56 percent to complete digesti- moved. In addition to the meals, digestibility bility. These values were largely from two studies, data for several other corn products have been re- a recent report b}^ McCance and Glaser, 1948 ported. Although most of these other studies (102), and a much earlier article by Harcourt and were not used directly they have been included in Fulmer, 1907 (62). The range in digestibility of appendix table 23 and were helpful in that the fat found by McCance and Glaser was 62.5 to digestibility coefficients tended to confirm the 77.6 percent. In their experiments, six subjects averages for the two cornmeals shown in table 16. were fed a mixture of two oatmeals, having an Data for only three digestion trials were found in average fiber content of 0.9 percent, supplemented which sifted whole-ground cornmeal was used. with a little bramble jelly or skup. The daUy The average coefficient of digestibility of the meal intake of 34 to 67 grams of fat was supplied eaten in the form of corn bread by three subjects entirely by the oatmeal.

32 A very wide range, 57.6-97.9 percent, in the (d) Polished rice (white rice).—Rice which coefficients of digestibility for fat in oatmeal was had been pohshed perfectly, so that the germ calculated from data in 16 experiments published was almost entirely rubbed off in the milling. by Harcourt and Fulmer (62). These investi- The actual amounts of the rice kernel removed in gators tested four oatmeals with fiber contents of the polishing differ somewhat with the variety of 1.94, 1.15, 1.12, and 1.04 percent. Seven subjects rice, but about 4 percent of the unpolished rice participated but not all subjects ate each of the kernel was removed in making the half-pohshed rice, four meals. The daily intake of 58-120 grams of nearly 6 percent in making the 70-percent polished fat was supplied by oatmeal and either milk or rice, and approximately 7 to 8 percent in making cream, with about one-fifth to one-third of the the fully pohshed while rice. According to one total contributed by oatmeal. For the purpose article in the series no polishing powder was used. of calculating the digestibility of the fat in oat- Judging from other information given, the unpol- meal from data supplied we assumed the digesti- ished rice may have been the same as brown rice; bility of the fat of milk and cream to be 95 percent. the ha If-polished rice may be considered as an To the extent that this average figure may not be extraction of about 96 percent of the brown rice; applicable for these specific experiments there may the 70-percent polished, as an extraction of about be some error in our calculated results for oatmeal. 94 percent; and the polished rice, about a 92-per- The da ta from Harcourt and Fulmer suggest that cent extraction. On the basis of paddy or rough there may be some relation between digestibility rice, which is a more common basis for expressing and fiber content of oatmeal. When the oatme-als milling yields, the extraction rates, assuming the of both 1.94 percent fiber and lower fiber contents loss in removing the hulls to be 21 percent, would were fed to the same subjects under similar experi- be about 79 percent for brown rice, 76 percent for mental conditions, the fat digestibility of the oat- half-polished, 74 percent for 70-percent polished, meal of 1.94 percent fiber was lower than that of and 73 percent for polished white rice. samples with the much smaller percentages of Rubner (14-4) ^^^ í^lso Snyder (167) studied the fiber. Of interest in this connection are results digestibility of rice when eaten by men subjects reported by McCance and Glaser (102) who as part of very simple diets. Probably the rice found that the substance or mixture of substances used was ordinary white rice but it was not de- which they estimated as fiber in oatmeal passed scribed in either study. The number of experi- through the gut almost without change. The ments in which Europeans and Americans were results raise several questions. Is intestinal motil- subjects was too small to permit a good comparison ity related to the fiber content of oatmeals and if but there appeared to be no marked difference in so does this affect the digestibility of fat? To digestibility of the rice for the Japanese men who what extent do metabolic products account for fat very likely were accustomed to eating it as a major (ether-extractable matter) in the feces? The ex- item in their diet and for the German and American perimental evidence is inadequate either to inter- subjects who probably had it only occasionally. pret the widely divergent coefficients found or to The average coefficients of digestibility for the determine which part of the range would be closer unpolished (brown) rice, based entirely on the to the true value. The Atwater energy factor, Japanese studies, were 75 percent for protein and 8.37 calories per gram of fat in cereals and other 98 percent for carbohydrate; for half-polished rice plant foods in general, therefore has been used the coefficients were 82 and 99 percent, respec- without change for fat in oat products. tively, for the two nutrients, and for 70-percent Rice polished rice, 83 and 99 percent. For white rice the average coefficients of digestibility based on The most extensive study on digestibility of rice data reported by Saiki, Rubner, and Snyder were was carried out in a series of experiments by Sugi- 84 percent for protein and 99 percent for carbo- moto, Higuchi, Momyeda, Tonaka, Yasuda, and h3^drate. others and was published by Saiki in 1926 (178). The energy factors we suggest for the protein The subjects, all Japanese men, ate rice as part of and carbohydrate of bro^vn rice are 3.41 and 4.12 a mixed diet. The rice used was of four categories calories per gram respectively, and for white rice, which were described in one of the articles as 3.82 and 4.16. follows: (a) Unpolished rice.—Rice from which the Rye husk had been removed, but which still retained Many of the digestion experiments on rye flours the outer layer, or silver skin, and the embryo were conducted years ago in Germany. In some or germ. studies the diet was simple rye bread or rye bread (b) 50% polished rice.—Rice which had been and beer. Some of the subjects who were un- milled and polished but which retained half of accustomed to eating large quantities of rye the outer layer and germ. bread experienced pain in the digestive tract and (c) 70% polished rice.—Rice which still re- in some cases diarrhea, a factor that might vitiate tained about 30 percent of the outer layer and the digestibihty figures. But on the basis of the germ. data reported there was no clear-cut means of

33 eliminating this factor. In other experiments calories per gram of protein and 3.78, 3.86, 3.99, there was more variety in the diet but on the and 4.07 per gram of carbohydrate. whole the diets were simple. Kesults indicate no appreciable differences in digestibility when sub- Other grains jects had rye bread alone or as part of simple For grains and grain products not included in mixed diets. table 16 very few digestibihty data are available. Rye flours have been described as dark, whole- Amon,c^ the reports on these products is one by grain meal, medium, and light, and the following Woods and Snyder (196) which summarizes the data on their composition have been cited as results of the digestion experiments on cereal being representative for these products {100, 185) : foods at the Connecticut (Storrs), Mame, and Minnesota Agricultural Experiment Stations. Whole- For pearled and flaked barleys, Woods and Constituent Dark grain Medium Light meal Snyder apphed their estimated coefficients ol digestibihty of bariey products, 78 perceixt for Percent Percent Percent Percent protein and 94 percent for carbohydrate, i hese Water 11. 0 11. 0 11. 0 11.0 products had undergone some reíinenaent and m Protein 16.3 12. 1 11.4 9.4 Fat 2. 6 1.7 1.7 1.0 chemical composition were much like modern Ash - _____ 2. 0 1.8 1. 1 . 7 pearled bariey (185). The energy factors for Fiber 2. 4 2.0 1.0 . 4 pearied bariey, calculated from these coefficients Carbohydrate, total by dif- 68.1 73. 4 74. 8 77. 9 by use of the customary heat of combustion of ference grain products, are 3.55 and 3.95 calories per gram of protein and carbohydrate, respectively. For buckwheat flour, 'Jarina,'' and groats, Woods As there are no standards of identity for these and Snyder estimated digestibility at 78 percent products, much variation may be expected in for protein and 94 percent for carbohydrate. appearance and composition of samples of a given Their composition data indicated that the products designation or grade. For example, light rye has were refined forms, the fat, fiber, and ash content been described as ranging from white to mediuin- of 1.2, 0.4, and 0.9 percents for the flour being light fiour with a comparatively wide range in comparable to composition of modern light buck- proximate composition. In these circumstances, wheat flour. The above coefläcients of digestibility it was difficult to determine the type of ffour used applied to the heats of combustion for protein in the early digestibility studies. However, there and carbohydrate in cereal products result in the is a marked decrease in fiber and ash content following energy factors, 3.55 calories per gram with increasing degree of refinement, and the ash of protein and 3.95 calories per gram of car- content reported for the rye flours studied in the digestion experiments served as a criterion for bohydrate. deciding in which of the above four categories— For dark buckwheat flour, we have found no dark, whole-grain, medium, or light—to include experunental work on digestibility. The figures the data. in table 13 have been calculated arbitrarily from Little information is available on digestibility data for light buckwheat flour, assuming that the of medium and dark rye flours. However, the ratio of digestibihty of dark to light flour would be relationship of the digestibilities of either protein the same as that between whole-wheat flour and or carbohydrate observed between the light and wheat flour of intermediate extraction. Judging whole-grain rye flours was similar to that observed by the ash content, the light buckwheat flour may between the straight patent and whole-wheat have been comparable in degree of refinement to flours. On the assumption that this similarity in wheat flour of intermediate extraction and the ratios can be extended to include intermediate dark buckwheat flour to whole-wheat flour. The extractions of rye and wheat flours, digestibihty coefficients of digestibility thus assumed for dark values for other extractions of rye flour were buckwheat flour were 74 percent for protein and imputed from ratios for wheat flours where data 90 percent for carbohydrate, and the energy factors on rye flour were lacking. Ash content was taken were 3.37 and 3.78 calories per gram, respectively. as a general index of the degree of extraction of For wild rice, data are also to be found in the the flour. Thus for rye flours of the composition summary by Woods and Snyder. They report the shown in Agriculture Handbook No. 8 (185) and coefficients of digestibility to be 78 percent for described as dark, whole-grain, medium, and protein and 94 percent for carbohydrate, which light we estimated the digestibility of protein as would result in energy factors of 3.55 and 3.95 65, 67, 71, and 75 percent and the corresponding calories per gram, respectively. digestibility of the carbohydrate as 90, 92, 95, Sorghums and millets, while little used in this and 97 percent, respectively. Using these coeffi- country for human consumption, are important cients of digestibility and Atwater^s heats of foods in some parts of the world. In sections of combustion for cereals, the energy factors to the Far East, both grains are used extensively, apply to dark, whole-meal, medium, and light rye frequently prepared as a mush or ground into meal flour are, respectively, 2.96, 3.05, 3.23, and 3.41 and used in bread.

34 Langworthy and Holmes (93) conducted experi- We question whether the higher coefficients for ments with the dual purpose of comparing the protein indicated by the experiments on Japanese digestibilities of the different kinds of sorghums— subjects, possibly accustomed to eating kaoliane; kaoUang, feterita, kafir, and milo—and the digesti- are applicable for measuring digestibility in persons bihty of sorghums in general with that of other with an entirely different dietary pattern. Further- cereals, namely, wheat and corn. The grains were more, we need to consider the composition of the ground in the same mill and put through a 16-mesh other foods used with the sorghums. In many of sieve. By this treatment 5 percent of the bran was the experimental diets of Langworthy, fruit, either removed from kaoliang, 15 percent from feterita, oranges or applesauce, was a major item. 19 percent from milo, and 21 percent from kafir. The data available do not provide a good basis The differences in the structure of the grains for deriving a satisfactory figure for the apparent probably account for the different amounts of the digestibihty of sorghum protein. The variations ground meals that passed through the 16-mesh observed were extremely wide and the particular sieve, being largest for the softer kaohang which extractions used for the Langworthy experiments grmds more readily than the corneous types. The may not be typical of the sorghum meals ordinarily portions of the wheat and corn kernels removed used for food. A kaoliang meal of 95-percent was not stated. Each of the sorghums was used as extraction may not be t3^pical but is not far short bread or as mush; the corn and wheat as bread of whole meal. If a factor for whole-meal sorghum only. or nearly whole meal is needed, we suggest as a In one of the kafir bread series the remainder of tentative factor 0.91 calorie per gram of protein. the diet consisted of milk, orange, and sugar. This is based on a digestibihty of 20 percent, indi- Otherwise, the diets in the bread series had in addi- cated by the work of Langworthy and Holmes for tion to the bread, applesauce, butter, sugar, and in kaoliang and the usual heat of combustion for most cases, potato. In the series containing mush, protein in cereals. We recognize the possibihty the diet was similar except that potato was that for persons accustomed to eating kaohang, omitted so that essentially all of the protein would this factor may be too low and that it may not be supplied by the test food. be equally apphcable to sorghums other than Whether a sorghum meal was served as bread or kaoliang. as mush appeared to have had httle influence on its Millet also was studied by Langworthy and digestibihty. The carbohydrate was well utilized Holmes (94). The experimental plan was similar in all the sorghums; the average digestibihty for to that used for sorghums. Two millets were the kaoliang was 96 percent and the carbohydrate studied, common millet. Setaria itálica, from of the other sorghum meals was as well or better which 40 percent of the bran portion was removed, utilized. Using 96 percent and 4.20 calories per and proso millet, Panicum miliaceum, from which gram as the heat of combustion, the energy factor 29 percent bran was removed by sifting the for carbohydrate is 4.03. meals through a 16-mesh sieve. Both were fed The digestibihty of the protein was extremely as bread in a simple mixed diet of potato, orange, variable but considerably lower than that found butter, and sugar. for the protein in either wheat meal or cornmeal. The utilization of carbohydrate in millet was Feterita and kafir, both hard corneous types of about like that for the sorghums. The average sorghum, showed similar average protein digesti- digestibility observed for the carbohydrate of each bihty, approximately 50 percent. Milo is a some- of the millets was high, 96 percent. The digest- what softer type with a larger proportion of starchy ibility of protein of both millet meals was variable endosperm; its average protein digestibility was but was low, averaging approximately 40 percent about 40 percent. Kaoliang, which is very soft for each kind. For millets as for the sorghums and has a high proportion of starchy endosperm, these samples prepared as described may not be had a very low digestibihty, slightly less than 20 at all comparable to the millet meals actually percent. used. We have not attempted to derive calorie In an experiment conducted by Abe and others factors for millets but have called attention to (^) with Japanese subjects, when kaoliang was the this work since anyone needing data on millets main food in a mixed diet, the average digestibility may be able to adapt the information to their of the protein in the total diet was 77 percent and purpose. the carbohydrate, 99 percent. No estimate was Other grain products include various refined made for the sorghum alone. For the total diet cereal foods such as breakfast foods prepared the averages in the Langworthy and Holmes from a mixture of grains and also starches and experiments were lower, only 24 percent for protein flour mixtures. For some a few scattered data in the diets containing kaoliang, and 42 to 64 per- are available but the experimental conditions were cent for protein in the other sorghum diets; for not always such as to make them suitable for use carbohydrate, 96 percent in the diets containing in obtaining representative coefficients of digest- kaoliang and a range of 96 to 97 percent in the ibihty. In lieu of satisfactory data, Atwater's diets containing the other sorghums. The digesti- group factors for cereals were used for these bihty was lower in the experiments of Lang- various products. His factors, 3.87 calories per worthy and Holmes, particularly for the protein. gram for protein, 8.37 for fat, and 4.12 for carbo- 35 hydrate, were predominantly weighted by refined stituents with a healthy man engaged in I^^^Í^' cereals and therefore should give a fairly close ately actiye laboratory work as the subject. I^® approximation of the energy yalue of foods that digestion experiment was carried out according to ciistomary procedures. The methods of analyses haye undergone considerable refinement. employed were those used by Street and Bailey (17A) "^ Analyses were made of both the soybean Legu mes meal and the feces resulting from a ration of soy- bean meal porridge, milk, butter, and cane sugar. The array of data on digestibilitv of foods in Bowers reported the coefficients of digestibility the dry legume group (see appendix table 23) for the carboh^^drates of cooked soybean meal as shows that seyeral studies haye been made of the follows: Dextrin and starch, 99 percent; sucrose, more important items. For beans, peas, and 100 percent; raffinose, 100 percent; organic acids, soybeans the digestibility of carbohydrate (deter- 99 percent; pentosans, 93 percent; galactans, 9b mined by difference) was high, ayeraging 96 to 98 percent; cellulose, 79 percent; and the remaining percent; for cowpeas it was lower, about 90 fraction, presumably waxes, color principles, and percent. These high coefiicients suggest possible possibly undetermined hemicelluloses, 94 percent utilization of some of the fiber and pentosans. by difference. By calculation from the separate Data are inadequate to explain the disappearance constituents he arriyed at a digestibihty coefficient from the gut of much of the complex carboh^^drate of about 94 percent as compared mth 96 percent matter. Results of some inyestigations indicate which he found independently for total carbo- that some are split by means of bacterial action hydrate by difference. into their simpler components and ultimately Entirely different results for digestibility ol^ the into end products that may be discarded by the carbohydrate of uncooked soybeans were obtained body. To what extent intermediate products are by Adolph and Kao (3) in a series of m yitro absorbed is an unanswered question. experiments in addition to in yiyo digestibility Both the kinds and amounts of carbohydrates experiments with rats. They estimated the ay ail- present are of particular interest in comparing ability of soybean carbohydrate to be about 40 digestibilities of yarious legumes. Some legumes percent. This figure has been widely used in are similar in their content of moisture, protein, assessing soybean carbohydrate {36, 37, 185), but fat, ash, and total carbohydrate by difference, its application to so^^beans for human use seems but seyeral experiments indicate that the similarity questionable. does not hold for indiyidual carbohydrates. In the manufacture of soybean curd and milk, Differences in digestibility might be more easily much of the carbohydrate fraction is remoyed and understood had more information been obtained the carbohydrates that are left appear to be almost on the makeup of the carbohydrate fraction in completely digested. A digestibility coefficient of the legumes samples used. Data in the literature 98 percent was found for curd in a Japanese indicate that the proportion of the total carbo- experiment {13If). h3''drate (by difference) in the form of the so-called Although there may be significant differences ayailable carbohydrates, mainly starch, sugar, and in digestibility of carbohydrates in different leg- dextrin, is less than one-half for cowpeas, two- umes as indicated in the yery few studies ayail- thirds to more than three-fourths for beans able, it does not appear wise at the present time (kidney, lima, mung) and chickpeas, 85 to 90 to depart from the group factor, 4.07 calories per percent for lentils and peas. The total amount gram, originally used by At^yater for carbohydrate of crude fiber plus pentosans yaried for the seyeral in legumes. foods, 12 percent for kidney beans, 10 percent for A large number of studies has provided data mung beans, 13 percent for chickpeas, 10 percent on the apparent digestibility of protein in leg- for cowpeas, and 7 percent for lentils. The umes. Although some yariation may be observed undetermined fraction makes up a relatiyely (see appendix table 23) the data on the whole large portion of the total carbohydrates in beans support the digestibility and energy factors used and cowpeas but only a small percentage in the by Atwater. They are suggested here for use other legumes. For soybeans as much as two-thirds of the with soybean curd and milk because the data in total carbohydrate is made up of the carbohydrate the literature are too variable to indicate whether fraction usually considered to be of questionable or not the factors for either protein or carbohydrate ayailability. In this fraction a yariety of sub- are applicable to these two products. stances has been found in widely yarying amounts. These include raSinose, stachyose, pentosans, ga- Nuts lactans, arabans, cellulose, lignin, organic acids, pbytin, and glycosides. In addition to these Nuts present problems regardmg digestibility some waxes, color principles, tannins, and undeter- and composition similar to those of the legume mined hemicelluloses are belieyed to be present. group. Little has been reported on their digest- Bowers (£9) studied the composition of the ibility and it is difficult to evaluate the few results complex carbohydrate fraction of defatted soy- that have been published. The most extensive bean meal and the digestibility of separate con- work on this food group was reported by Jaffa

36 (75), who determined the digestibihty of diets simiilar romplf^x carbohydrate constituents, and a composed of fruit and nuts in 28 experiments. like amount as undi^tormined matter. Almonds The kinds of nuts studied were almonds, Brazil appear to have a lower proportion of sugar and nuts, coconuts, pecans, walnuts, and peanuts, a starch, averaging around 40 percent, and have legume which is used like nuts. In 20 of these about 25 percent in the form of complex carbo- experiments, in which most of the protein was hydrates that are of questionable availability. supplied by nuts, the average digestibility for the The nature of the remaining portion is undeter- dietary pro tern was about 75 percent. This value mined. The limited data for peanuts are too is lower than usually is found for mixed diets m variable to estimate the proportions in which the which plant foods predominate. Possibly the low carbohydrate components are distributed. apparent digestibility was the result of the large As readily can be seen, the information on the quantities of fruit consumed. Unfortunately the composition and the digestibility of the carbo- effect of the amount and kind of carbohydrate hydrate fraction of nuts is far from complete. from the fruit on the digestibility of the protein Therefore, it appears best to continue to use the and fat in the nuts could not be determined from coefficient, 97 percent, assigned by Atwater to these studies. carbohydrate in legumes and nuts, and his energy The apparent digestibility of the protein of factor, 4.07 calories per gram. nuts alone estimated from these 20 experiments by use of Atwater's figure of 85 percent digesti- Vesetables bility for fruit protein, ranged from 54 to 87 per- cent, averaging 70 percent for nuts as a group. Very few digestibility studies of vegetables had From the two experiments on peanuts the calcu- been made when Atwater proposed for all vege- lated coefficient of digestibility for protein would tables as a group the factors 3.11 calories per gram be 81.5 percent. These figures may be too low for protein and 3.99 calories per gram for carbo- since the calculation is dependent on the digesti- hydrate. Data accumulated since are still limited bility of the whole diet. Holmes (70, 72) found a but provide some basis for separate factors that much higher digestibility, 92 percent, for peanut may be applied to smaller groups of vegetables. protein. He used a simple mixed diet which included either pressure-cooked peanuts or baking Potatoes powder biscuits that had been made with peanut Potatoes have been studied more than other flour. The peanuts Jaffa used were not described; vegetables; results from 10 investigations have presumably they were ordinary roasted peanuts. been noted in the literature. In most cases the In diets in which boiled or roasted chestnuts con- composition of the samples used in the digestion tributed most of the total protein intake Heupke experiments was not reported. and others (67) found that the digestibility of The average digestibility coefficients fou ad for chestnut protein ranged from 68 to 79 percent. protein by the 10 investigators were from 64 to 85, In view of the variable results for peanuts and averaging 74 percent. These are surprisingly low for nuts, there is no good basis for estimating values and we consider them tentative estimates. digestibility of protein in nuts of different kinds In several of the experiments the total protein or even as a group. It is preferable to continue intake was low. Potatoes contain very httle to use, as an interim value for nuts, Atwater's nitrogen, only about 0.3 percent, but several group coefficient for protein in legumes, 78 per- observers have pointed out that subjects have cent. The grouping of nuts with legumes is a remained in generally good physical condition for common practice and has some basis since there long periods of time on diets in which potatoes are many points of similarity in the proximate are practically the sole source of protein. composition of these two food groups. One such study was reported by Kon and Klein, Very little work on the digestibility of carbo- 1928 (83), who conducted digestion experiments hydrate material in nuts has been reported. Only over a period of 167 days. The two subjects, a a small fraction of the total carbohydrate intake man aged 25 and a woman aged 28, remained in was furnished by nuts in Jaffa's series of experi- nitrogen equilibrium and in apparent good health ments and the digestibility of carbohydrate in on a very simple diet mth the daily intake of nuts has not been estimated. Merrill (IW) found nitrogen chiefly from potatoes, averaging only 5.7 that more than 98 percent of the carbohydrate in grams for the man and 3.8 grams for the woman. chestnut flour was digested. Heupke and others The coefficients of digestibihty of the potato pro- (67) found digestibilities ranging froni 96.5 to 99.9 tein were 66 and 62 percent respectively for the percent in several experiments in which chestnuts man and woman. were fed as raw flakes or cooked by boiling or Three subjects in the study by Hmdhede, 1913 roasting. (69), also were on simple diets in which potatoes Data reported in the literature on the composi- contributed nearly all the protein over an ex- tion of various nuts indicate that most nuts con- tended period of time. The diets were planned tain from one-half to two-thirds of their carbo- to provide the minimum protein intake at calorie hydrate in the form of sugars or starch or both, levels just sufficient to maintain nitrogen equi- up to one-third as crude fiber, pentosans, and hbrium. The digestibility of the potato protem 37 present are lignin, cellulose, pentosans, pectin , ranged from 71 to 86 percent. For 9 months and other hemicelluloses, but the complex car DO- one subject, M, had a daily nitrogen intake from hydrate constitutents of doubtful avaüaDUiiy 5.8 to 8.4 grams and maintained a schedule of appear to make up only about 1 to 3 percent ot varying activity, including 3 months of hard labor, the potato. Sugars have been found m varying without any apparent Si effects—his excellent amounts, from less than 1 to as much as 6 V^l^^^- physical condition at the end of the period was The quantities of dextrm present are small. confirmed by four physicians. The apparent Starch makes up nearly all of the remammg carbo- digestibiUty of the potato protein in this case averaged 84 percent. ^^lî^a^recent compUation the following average In a 10-day experiment Rose and Cooper {H2) data were obtained: Carbohydrate by àf^^^n^^^^ also observed good utilization of potato protein. 19.1; starch, 17.1; sugar, 0.3; crude fiber, 0.6; The subject, a woman, was able to maintain and undetermined, 1.1 percent. This last fraction nitrogen equilibrium, after the third day, on a may contain pentosans, pectins, and other carbo- diet of potato, sugar, and agar-agar, which pro- hydrate constituents not determined as crude vided a relatively low nitrogen intake, 4.8 grams fiber by the Weende method. It has been sho^vn per day. The apparent digestibihty was 74 by Remy {189), Wühams and Olmsted {^87).^^ percent. The detailed analyses reported on the nitro- Weinstock and Benham {186) that this method genous fractions of potatoes by Street, Kenyon fails to measure much of the total fiber. and Watson, 1946 {178), Crook and Watson, For potatoes it seems to us best to continue the 1948 iU), Neuberger and Sänger, 1942 {ISO), use of the heats of combustion which Atwater and Headden, 1927 {65), indicated that most of assumed for potatoes and other vegetables (see the nitrogenous matter in potatoes would be table 7). As a check on the application ol these available. The proportions of the different nitro- factors to potatoes, we calculated gross heats genous materials vary greatly from sample to from the chemical analyses of three samples sample, the coagulable fraction (proteins, proteoses, and compared the results of our calculation with peptones) ranging from 30 to almost 75 percent values determined in the bomb calornneter for and averaging around 40 percent, and the amino the same samples. Data from protein, fat, and acid fraction from 30 to 60 percent, averaging carbohydrate analysis and from the bomb calo- about 50 percent. Of the small remaining frac- rimeter were taken from a study of Bryant and tion, 2 to 6 percent has been determined as Milner {88). Close agreement between the deter- ammonia and nitrate nitrogen. mined and calculated heats of combustion was Of more practical significance than nitrogenous found as shown in table 17. The energy factors compounds in estimating energy values for we derived for potatoes were 2.78 calories per potatoes are data on digestibility and composition gram for protein and 4.03 calories per gram for of the carbohydrate fractions. Results from six carbohydrate. They were derived by applying studies reporting digestibility of total carbohy- average coefficients of digestibility found in the drate ranged from 92 to more than 99 percent, literature, 74 percent for protein and 96 percent with an average of 96 percent. These values for carbohydrate, to the heats of combustion, appear reasonable in view of the high proportion 5.00—1.25 and 4.2 calories per gram, respec- of starch, sugar, and dextrin in potatoes. Also tively.

TABLE 17.—Comparison oj determined and calculated gross energy values of potatoes

Heat of combustion per 100 Composition grams

Sample number Calculated i Carbohydrate Bomb calo- Protein Fat Fiber Ash from com- Water by difference rimeter position

Percent Percent Percent Percent Percent Percent Calories Calories 1 79.5 2.2 0.1 17. 4 0.4 0.8 84. 8 85.0 2 78.3 2.3 . 1 18.4 .9 90.0 89.7 3 81.2 1.9 ,3 15.5 1. 1 78.2 77.4

1 For heat of combustion factors used see table 13, page 25.

Other vegetables and those for potatoes to starchy roots and tubers. For other underground vegetables such as beets, Because published data are lacking on the carrots, onions, parsnips, and radishes we have digestibility of many vegetables, we have applied applied the energy factor for protein and the group factors—the energy factors for dried legum.es coefficient of digestibility for the carbohydrate to immature shelled beans, peas, and other in potatoes, but have made an adjustm.ent in the legumes, those for fruio to rhubarb and tomatoes, heat of com.bustion factor generally used for

38 vegetable carbohydrate to correct for the rela- accurate estimate for these substances we have tively large proportion of sugar. We assumed used the heat of combustion of vegetables, 5.00 that from two-thirds to three-fourths of the calories per gram, for nitrogenous m.atter in carbohydrate in most of these underground vege- mushrooms. tables is present as sugar, and one-thii^d to one- Very little work has been noted on the digesti- fourth as starch and fiber. On this basis the bility of the nitrogenous matter of mushrooms. weighted heat of combustion would be 4.00 Saltet {152), in a 2-day study of a 31-year-old calories per gram and the energy factor calculated man, found that his subject digested 69 percent for carbohydrate, 3.84 calories per gram. of the nitrogenous matter when mushroom.s com- Coef&cients of digestibility for protein and bined with a little butter and seasonings were carbohydrate in the few vegetables for which fed. A similar result, 72 percent digestibility, data have been reported vary widely. We was obtained by Skinner, Peterson, and Steenbock rounded the median figure for digestibility of {161) when mushroom.s were fed to albino rats. protein, based on 14 experiments, to 65 and have A digestibility coefficient of about 70 percent used it rather than Atwater's figure of 83 percent. seems a reasonable estim.ate and following the The carbohydrate fractions are an important usual procedure of applying it to the heat of com- source of energy in some vegetables. We have bustion, 5.00 calories less 1.25, we derive an used a coefficient of 85 percent, the median value energy factor of 2.62 calories per gram of nitrog- for 13 experiments on a variety of vegetables, in enous matter. place of Atwater's figure of 95 percent. For the The carbohydrate fraction of mushroom.s also remaining vegetables except mushrooms we have includes a variety of components, not all of which calculated the energy factors by applying diges- have been determined quantitatively. tibilities of 65 percent for protein and 85 percent One of the most complete analyses of carbohy- of carbohydrate to the heats of combustion used drates m mushroom.s reported to date was made by Atwater for vegetables. The energy factors by McConnell and Esselen {109), but 51.8 percent obtained in this way are 2.44 calories per gi^am for of the total carbohydrate was still unidentified. protein and 3.57 calories per gram for carbo- The data from this study expressed as percent of hydrate. fresh mushrooms and as percent of total carbohy- drate follow: Mushrooms Reports in the literature cover various aspects Content Proportion of the composition of the nitrogenous matter of Carbohydrates in mushrooms on fresh of total (Agaricus campestris) carbo- mushrooms, but as yet there is no complete picture basis hj'^drate of the quantitative distribution of the various constitutents. From 63 to 72 percent of the total Percent Percent nitrogen has been termed ^'protein nitrogen" {53, Total carbohydrate (by difference) __. 5. 75 100. 0 Mannitol .95 16. 5 123, 175). Other known constituents are free Reducing sugars (as dextrose) .28 4.9 amino acids, amides, purines, and am.m.onia. In Pentoses, methyl pentoses, hex som.e instances appreciable am.ounts of urea have uronic acids . 04 . 7 Glycogen .59 10.3 been determined. Iwanoiï (73) reported that . 91 15. 8 amino acids are formed autolytically during the Crude hemicellulose ripening period before spore formation and are in turn changed into urea. He found that urea was several times as high at the ripened stage as in Other carbohydrate constituents that have been the young immature mushrooms, and that in some reported as occurring in mushrooms include cellu- samples the urea nitrogen approxim.ated half of lose, lignin, trehalose, indican, and amino-hexose. the total nitrogen. Mendel {116) suggested that The published data indicate that not only is the som.e of the nitrogen in m.ushroom.s is bound with total carbohydrate fraction complex but also that cellulose and that all attempts to separate the some of the components vary in amounts, possibly nitrogenous constituent from, the portion that depending on variety and other factors such as yields sugar on hydrolysis had failed. drying and storage. Thus it is apparent that use of the conventional There is no very reliable information from which factor 6.25 to convert nitrogen to protein intro- an estimate of the digestibihty of the carbohy- duces an error in the value for the nitrogenous drates in mushrooms can be obtained. Only one matter, but at present there are insufficient data digestion experiment, reported by Oshima {134), to provide a better factor. Hence, we have con- has been noted in the literature. The subject, a tinued to use the factor 6.25 in calculating total Japanese army surgeon, was on an experimental nitrogenous material in m.ushrooms, although we diet consisting of 74 grams of dried mushrooms realize that the error involved may be of some (Agaricus sitake) and 40 grams of soy sauce lor significance. 1 day. According to the author a satisfactory Urea, as well as some of the other nitrogen- separation of the feces was obtained by the use of containing substances, has a lower heat of com- buckwheat flour. The digestibUity found for the bustion than protein, but since we could m.ake no carbohydrate was 84 percent

39 305774—55 4 For calculating the energy value of the carbo- Total Grams per Calories calories hydrate in mushrooms, Watt and Merrill {185) Constituent 100 grams per gram used a factor of 1.35 on the assumption that only 5, 6 mannitol, reducing sugars, and glycogen, which Invert sugar 1. 5 3. 75 account for approximately 33 percent of the total Citric acid (anhydrous) _ _ _ _. 6. 0 2. 47 14. 8 Fiber and unknown constit- carbohydrate, were available for absorption. The . 2 4. 2 data from the one digestibility study which has uents since been located suggests that such a procedure Total carbohydrate may underestimate appreciably the energy value. (by difference) 7.7 21. 2 Until additional digestibility data on mushrooms 1 gram carbohydrate =2 75 calories (21.2-^ 7.7). are available, it therefore seems preferable to use a digestibility coefficient of 85 percent as for most vegetables and to apply it to a heat of combustion value which corrects for the presence of appre- Since the fiber fraction of lemon juice is very ciable amoim,ts of sugars. Using the composition low and since both invert sugar and citric acid data of McConnell and Esselen and assigning may be com.pletely utüized, we took the figure heat of combustion values of 3.75 to mannitol, recommended by Atwater for sugar, 98 percent, as reducing sugars as dextrose, and pentoses, 4.19 a reasonable value for apparent digestibility. to glycogen, and 4.20 to the remaining fraction, The resultant energy factor was 2.70 calories per the resulting heat of combustion value for total gram of carbohydrate. Since lim.es are similar to carbohydrate becomes 4.1 calories per gram. By lemons in carbohydrate constituents we have applying the coefficient of digestibility, 85 percent, applied the sam.e energy factor for carbohydrate. to this value the energy factor for carbohydrate For lack of better data for other fruits we have in mushrooms is 3.48 calories per gram. continued to use the carbohydrate factor, 3.60 calories per gram, derived by Atwater. Likewise, his factors for protein and fat in aU fruits have Fruits been used. The energy from fruits comes largely from carbohydrate. The energy factor, 3.60 calories Miscellaneous foods per gram, was applied by Atwater to carbohydrate, Many specific foods have not been studied in based on the heat of combustion figure of 4.00 human digestion experiments, as can be seen from calories per gram and digestibility of 90 percent. the com.pilation on digestibility coefl&cients (ap- In arriving at this heat of combustion value he took into consideration that the carbohydrates of pendix table 23). In many cases when digest- fruits are a mixture of sugars, mainly lévulose ibüity data on individual foods were lacking, we and dextrose, but that starch, cellulose, pento- have used a general value for a group of foods for sans, and other complex carbohydrates are also each food in that group. In other instances when present. a food has undergone some treatment to change We consider 3.60 a reasonable group factor and its form, the energy factor of the food in its have applied it to most individual fruits, but with original form has been applied to the product or full recognition of the possible inaccuracies products. These procedures no doubt result in involved. For example, the coefficient of digesti- some errors. bility 90 percent is probably too low for fruit Where the above procedures were not applicable juices and for sweetened canned or cooked fruit. and when the m.ethods of estimating the energy The group factor for heat of combustion of factors differed in some respects from the general carbohydrate in fruits will not apply equally well procedure usually followed, these deviations will to individual fruits. A compilation of the proxi- be explained in turn for the several miscellaneous mate composition of fresh fruits {38) showed foods. considerable variation among fruits in the pro- portions of sugar, starch, acid, and crude fiber Chocolate and cocoa present. There is need for revision and extension Chocolate and cocoa present a variety of of this compilation to include data available since problems in regard fco both chemical composition its publication, particularly with respect to the and digestibility. Determ.inations of various ni- carbohydrate constituents, before further esti- trogen-containing compounds have been made in mates for heats of combustion of carbohydrate in a few studies. It appears that from 12 to 23 individual fruits are made. percent of the total nitrogen present is in the form Attention is called to lemons in particular, of alkaloids, mainly theobromine and c-afîeine, since they have considerable citric acid with a and 1 to 9 percent as ammonia, and that the heat of combustion of only 2.47 calories per gram. remainder, although not clearly identified, m.ay be As the value 4.00 would be too high for the heat in the form of protein or protein derivatives. of combustion for total carbohydrate (by differ- Data reported by Stutzer {177) are the most ence) in lemons and lemon juice, we have used complete of the analyses located and seem to be 2.75 derived by the following calculations: representative values when compared with several 40 less complete analyses made by other investi- (8 cups), respectively. Schlesinger {153) found a gators. Stutzer analyzed several kinds of cocoa. digestibiUty of about 86.5 percent for protein in For one product which had not been treated with a mixed diet consisting of milk, meat, refined alkaline chemic^als (potash, soda, or amm.onia) he cereal, and fat, whereas when 60 grams of cocoa found that 16.6 percent of the total nitrogen was were eaten in addition the digestibiUty of the from alkaloids (mainly theobromine), 1.4 percent protein of the total diet was slightly lowered and from, ammonia, 6.3 perceut from amides, and was about 84 percent. Beddies, as reported by 75.8 percent from other nitrogenous matter. Neumann {131), also found the digestibility of Using these data, we have calculated the gross protein to be about 84 percent for a mLxed diet energy per gram of total nitrogen in cocoa as which included 50 grams of cocoa. Cohn {If.1) follows: obseiwed a lower digestibility coefficient, 75.5 per- cent. His diet differed from those of vSchlesinger and Beddies mainly in that larger amounts of Nitro- Conver- Amount Heat of Gross cocoa, 100 to 130 grams, were used and milk was Compound gen per sion of com- combus- energy gram factor pound tion equiva- not included. lent Neumann has reported two studies on cocoa {131, Om. Gm. Cal./gm. Cal. 132). In one series of investigations he deter- Protein _ _ 0. 758 6. 25 4. 74 5.80 27. 5 mined digestibility of diets made up of sausage, Alkaloids as theo- brie cheese, rye bread, lard, and sugar, in which bromine _ . _ __ . 166 3. 22 . 53 5. 22 2. 8 Ammonia _ _ _ . 014 1. 22 .02 cocoa replaced equivalent amounts of protein and Amides as asparagin. .063 5. 35 . 34 3. 45 1. 2 fat of the diet. The digestibihty of the protein of the diet without cocoa averaged 82 percent. Wlien Total 1. 001 5. 63 31. 5 35 grams of cocoa were included in the diet, the digestibility dropped to 75 percent, decreasing still Gross energy equivalent of 1 gm. nitrogenous matter = 5.60 calories. further to 57 percent when the daily intake of cocoa was increased to 100 grams. In the second series, Neumann found very low digestibiUty of Digestibility of the nitrogenous portion of the cocoa protein, namely, 45 and 25 percent in cocoa was studied by some of the early German two experiments in which 35 grams of cocoa were scientists. In these studies there ^^as no atcempt eaten with 350 grams of sugar as the only other to distinguish between the protein and* non- food in the diet. Inasmuch as he corrected for protein fractions of the nitiogenous matter. In the nitrogen in the digestive juices in getting his some of the studies cocoa supplied all of the digestibility of cocoa, the apparent digestibility nitrogen, and in som.e the diet included other would be still lower. These results indicate that protein foods in addition to the cocoa. Experi- the digestibiUty of the nitrogen portion of cocoa ments conducted by Weigm.ann and by Lebbin, is considerably lower than that of the other foods reported through König {84, pp. 244-245), showed in the mixed diets studied. Unfortunately the the following results: For three kinds of cocoa fed digestibility of cocoa cannot be calculated in the in amounts of 188-304 grams per day along with several studies on mLxed diets and there is no sugar and water, Lebbin found protein digesti- means of determining whether the utilization of bility coefíicients of 41.1, 45.2, and 41.6 percent; cocoa as a ñavoring ingredient in the diet as it is for a diet of cocoa and beer or wine, Weigm.ann normally consumed is better than when it is used found a digestibility of 41.5 percent after correc- alone or with sugar only. tion for metabolic nitrogen. The apparent di- On the basis of studies in which cocoa was the gestibility was calculated to be 12.7 percent. For chief source of nitrogen, we have used a digestibil- two Idnds of cocoa, Neumann {1SÎ) reported that ity of 42 percent, although this may be too low Beddies found digestion coefläcients of 55.3 and for ordinary appUcation. When the 42 percent 54.1 percent. In these latter experim.ents, 150 figure is applied to 5.6, the heat of combustion grams of cocoa were consum.ed daily but no derived as shown above, less 1.25, an energy information was given on the remainder of the factor of 1.83 calories per gram of nitrogen- diet. containing material results. Information on the Several studies have been reported in which utilization of the nonprotein nitrogen is needed cocoa was eaten in combination with other protein- before a more accurate factor can be developed. The carbohydrates of chocolate and cocoa pre- containing foods. There is some indication that sent problems similar to those for the nitrogenous digestibility of the cocoa may be affected by the matter. Some unpublished data* for chocolate level of cocoa and its proportion of total dietary Uquor show the following complex composition: nitrogen, the combination of foods used with the 28.4 percent total carbohydrate by difference; 8.0 cocoa and possibly its preparation—whether raw percent starch; 2.8 percent fiber; 3.5 percent or cooked. Forster {66) found for a diet of milk pentosans; 2 to 3 percent gums and hemiceUulose; alone that the protein digestibility was 93 percent as compared with 93.2 and 92.4 percent for diets 4 Winkler, W. 0. Unpublished data. Food and Drug of milk and cocoa, with the latter taken in amounts Administration, U. S. Department of Health, Education, of 20 grams (2 to 3 cups of beverage) and 60 ^ams and Welfare [n. d.]. 41 9.5 percent products such as tannins and cocoa that 67 percent of the total N was amino N and red; 0.5 percent sugars, mainly glucose; 0.6 percent 7.5 to 16 percent was ammonia N. organic acids; and the remainder, undeterm-ined Funk, Lyle, and McCaskey {59) reported ex- matter. These data were used in estimating the periments in which a dried anaerobic yeast heat of combustion for the total carbohydrate (by preparation was eaten in a diet consisting largely difference). The value obtained was 4.16 calories of vegetables and fruits. The daily nitrogen per gram, using as heats of combustion 3.75 intake, mainly from yeast, was 5.9 grams and the calories per gram for sugar, 2.45 for organic acid, digestibility of the nitrogenous matter was esti- and 4.20 for the remaining constituents and weight- mated to range from about 60 to 80 percent, ing them according to the percentage composition averaging about 70 percent. Results of Murhn above. and others {125) indicated that the apparent Digestibility data for the carbohydrate of cocoa digestibihty of nitrogen in brewer's yeast was are even Jess conclusive than those reported for about 57 percent. The daily nitrogen intakes protein. In the few experiments located in which were very low, averaging 3.7 grams daily. cocoa was fed in mixed diets, the digestibility of The data indicate that the average apparent carbohydrate coidd not be calculated for the total digestibility of the nitrogenous matter of dried diet or for the cocoa. The experiments of Lebbin 3reast is probably in the range of 70 to 90 percent on diets of cocoa and sugar reported by König when the level of intake is fairly adequate. In {8/i) indicated that probably less than a third of deriving an energy factor, we have estimated the the tota] carbohydrate of cocoa is available to the coefficient of digestibihty as 80 percent. body. Here, as in the case of protein, this esti- According to an analysis of yeast reported by m.ate may be lower than actually found when Frey {58) the nitrogenous matter is composed of cocoa is used in a mixed diet. As a tentative 60 percent monoamino acids, 20 percent diamino coeiïicient, until satisfactory data can be obtained acids, 12 percent purines and p3?TÍmidine bases, on the digestibility of cocoa carbohydrate, we are and 8 percent ammonia. These data indicate using 32 percent. This was indicated both by that the heat of combustion is lower than if the the work of Lebbin and by the carbohydrate nitrógeno as matter of yeast were all protein. composition data above for chocolate liquor, Therefore, for yeast protein we used the heat of assuming the starch, sugar, and organic acids to be combustion 5.00 calories per gram that we applied almost completely digested and the remaining to vegetables. The digestibility coefficient, 80 constituents to be undigested. The energy factor percent, applied to 3.75 (5.00 less 1.25) results in calculated from this coefficient and the heat of an energy factor of 3.00 calories per gram. combustion factor 4.16 is 1.33 calories per gram. Very httle research has been noted on the com- position of the different specific carbohydrate Yeast constituents in yeast and none at all on their The utilization of yeast '^protein'^ has been a digestibilit}?-. Frey {58) has reported that 81.5 matter of great interest. A number of studies percent of the total carbohydrate is glycogen and have been reported on the digestibility of the 18.5 percent, such substances as cellulose and nitrogenous matter in yeast, but in only a few of gums. On the basis of these data we used 80 these were human subjects used. Kuen and percent as a tentative coefficient of digestibility Puringer {87) compared its digestibility in dried on the assumption that the glycogen is digestible and fresh compressed yeasts, presumably baker's and the other carbohydrates may not be. This yeast, fed in a mixed diet that furnished 10 to 11 coefficient applied to the heat of combustion 4.20 grams of nitrogen and 2,460 to 2,840 calories calories per gram, assumed for total carbohydrate daily. The estimated digestibility was 90 percent (by difference), resulted in the energy factor 3.35 for the nitrogenous matter of dried yeast but only calories per gram. 63 percent for the fresh compressed yeast. Dirr {50) reported experiments in which either Food mixtures dried yeast or animal sources of protein were fed To keep pace with marketing practices as well in alternate periods of 7 days each. The daily as buying habits, successive editions of food com- nitrogen intake in each case was 10.4 grams from position tables contain a growing proportion of the test food with additional 3.4 to 5.6 grams items that are food mixtures. Included are a from plant foods. The calorie intake for the four wide assortment of baked goods, meat and cereal subjects ranged from about 2,000 to 2,800. The mixtures, salad dressings, and others that are digestibility of the nitrogen of the total diet combinations of ingredients. Because the many averaged 87.5 percent in the period in which nitrogen was supplied largely from animal sources, food mixtures vary so much in the kinds and pro- and 83.4 percent in the period in which yeast portions of ingredients used, information on their predominated in the diet. These results indicate digestibility from experiments can scarcely be that the nitrogenous matter of the yeast was expected. If the weights of ingredients are almost as completely absorbed as animal protein. known, calorie factors per unit weight of total DÛT and Soden {61) referred to the yeast as wood protein, fat, and carbohydrate in the finished sugar dried yeast and estimated from analyses product may be calculated. For products in

42 which the proportioDs of ingredients are fairly product must be knowD in addition to the weights standard, the calorie factors once worked out may of the ingredients. Calculations indicating the be applied directly to data on the amounts of derivation of energy factors and of calories per protein, fat, and carbohydrate in the product. 100 grams of baking powder biscuits made with To calculate the calories for any given weight skim milk, item 98 in Agriculture Handbook No. of an item from its recipe, the weight of the finished 8 (185), are shown in the sample calculation below.

Sample calculation of energy factors for food mixtures (baking powder biscuits)

Protein Fat Carbohydrate (by difference) Weight Kind of data Specific Specific Energy Energy Specific Energy Weight energy value Weight energy Weight energy factor factor value factor value

Ingredients: Om. Gm. Cal.lgm. Cal. Gm. Cal.lgm. Cal. Gm. Cal.lgm. CaL Wheat flour, patent. 336 36.3 4.05 147. 02 3.0 8.37 25. 11 255. 0 4. 12 1, 050. 60 Fat-_ -_ 55 55. 0 8. 84 486. 20 Milk, skim 244 8. 5 4. 27 36. 20 . 2 8. 79 1. 76 12.4 3. 87 47.99 Baking powder. 16 Salt- _ - - 2

Total ._ 653 44. 8 183. 32 58. 2 513. 07 267.4 1, 098. 59 Weighted factor (per gram) _ _ 4.09 8. 82 4. 11 Baked yield: Total _ . 549 44. 8 58.2 267.4 100-gram portion. _ 100 8.2 4.09 33. 54 10.6 8. 82 93.49 52. 2 4. 11 214. 54

The factors 4.09, 8.82, and 4.11 calories per Similar calculations were made for the other units gram were applied to the protein, fat, and carbo- of weight given for this item in tables 2 and 3 of hydrate values of the baked biscuits, with the Handbook No. 8. resultant calorie value 342 calories per 100 grams.

PART IV. APPLICATION OF CALORIE FACTORS

The physiological fuel value of a food resulting available calorie values for the foods are antici- from applying the factors summarized in table 13 pated. to the amounts of protein, fat, and carbohydrate In using data on apparent digestibility for present is considered to be a measure of its avail- developing the energy factors shown in table 13, able energy. Attention is again called to the the assumption is made that the amount and interpretation of this term to connote that portion character of the fecal matter (protein, fat, and available to the body as a source of energy. The carbohydrate) present is dependent on the food; difference between total or gross calories of a food a low apparent digestibility could result from and available calories is the caloric value of the greater excretion of metabohc products caused by organic matter in the urine and feces. Whether that food, from incomplete digestion, or from a this fecal organic matter is entirely of metabolic combination of several causes. Whatever the origin plus bacterial residues and desquamated contributing factors are, the assumption is that tissue, or whether it usually or only under some the apparent digestibilities of the energy-yielding circumstances includes undigested protein, fat, or components of that food would not vary widely for carbohydrate residues also, is a question of very a subject on a reasonably adequate intake of the great importance in dealing with such problems nutrient. If the total intake of a nutrient in a as determining man's use of various foods as diet is very low, the relative proportion in the sources of specific nutrients. ^Vhen this question feces is too' high for satisfactory measurement by is resolved the information should be helpful this procedure. More information is needed on the effect of level of the foods on utilization of also in devising methods for estimating energy nutrients. Most studies in the Uterature at values of specific nutrients in food when fed in present are on rather extreme diets, for example, various combinations and at different levels; either very high or rather low levels of protein, present methods are actually not completely satis- and moderately high and very high levels of the factory for estimating available energy from the test food. Data are needed also for intermediate different nutrients. As a result of changes in levels, those which are more realistic in terms of method, however, no big changes in actual total common food practices. 43 for carbohydrate by difference. The gross calorie Comparison of calculated and determined values for food and feces were from bomb calo- available calories for diets rimeter determinations and were found to be 4,143 for the food and 418 for the feces. For comparison we also calculated the gross calories of the food. The end results obtained by use of the current The heats of combustion, 5.80, 9.30 and 4.20 factors (table 13) for estimating available energy calories, were applied to the protein, fat, and of diets have been compared with results obtained carbohydrate (by difference), respectively, of by direct bomb calorimeter determinations. An experiment conducted by Snyder {164) with a whole-wheat bread; and 5.65, 9.25, and 3.95 to subject on a very simple diet of whole-wheat these nutrients in the milk. The calculated gross bread and milk serves to illustrate the details of calories for bread (2,407) were a httle higher than calculation (table 18). Snyder's protein figures the determined (2,353), and the calculated gross based on the factor 6.25 for converting nitrogen calories for milk (1,737), a little lower than the to protein were recomputed with the factors 5.83 determined (1,790), but for the total diet the and 6.38 for the bread and milk, respectively; the calculated gross calories were in excellent agree- necessary adjustments were made in the figures ment with the determined. TABLE 18.—Summary oj steps Jor checking available energy values calculated by factors from table IS

Available energy Deviation of calculated available Weight of Carbo- Gross energy Type of data material Protein Fat hydrate Calculated energy from Determined by u# of determined by bomb factors 1 value

Food consumed in 2-day period: Bread made from whole- Grams Grams Grams Grams Calories Calories Calories Percent wheat flour 1, 020. 8 73. 9 12.9 442. 4 2,353 2, 045. 5 Milk 2, 500. 0 75.2 87.5 127.2 1,790 1, 582. 5 Total 149. 1 100.4 569.6 4, 143 2 3, 561 3,628 -fl. 9 Excreta : Feces (water-free) 97.0 17. 6 10.2 52. 1 418 Urine 3 164 Total ______. 582

1 Energy factors from table 13 applied to the protein, 3 7.9 X difference between amount nitrogen in food and fat, and carbohydrate: 3.59, 8.37, and 3.78, respectively, in feces. for bread and 4.27, 8.79, and 3.87 for milk. 2 Gross energy of food minus total energy of excreta NOTE.—Data used in this procedure taken from experi- (4,143-582). ment No. 171, Studies of Bread and Breadmaking (164). The urinary calories were 181 when determined The available energy of the diet determined by bomb, but 164 when estimated according to from gross energy values of food, feces, and urine Atwater's procedure by multiplying the grams of was 3,561 calories. When the average wheat and digested protein 131.5 by 1.25 calories. The wide milk energy factors for protein, fat, and carbo- range in the calorie to nitrogen ratio of the urine hydrate shown in table 13 were applied to the (p. 16) indicates that there is less satisfactory nutrient intake in this experiment, the figure agreement between the usual calculation of urin- obiained for available calories was 3,628, differing ary energy loss and direct determinations. In from the determined figure by 1.9 percent. As fact, with the difficulties of drying and burning pointed out earlier, the factor for fat in whole urine, it may be that much of the discrepancy is wheat may be too high since it is based on digesti- in the bomb determination. We have considered bility of 90 percent. If the average digestibility it advisable when estimating available energy is nearer two-thirds, as indicated in a number of data to use the calorie-nitrogen factor based on a experiments, the energy factor would be approxi- large num.ber of samples rather than a bomb mately 5.95; the figure for available calories, 3,597, determination of the particular sample of urine. would then be in even better agreement with the The calorie-N ratio for this individual was 6.9, determined value, differing by only 1.0 percent. which is lower than the average but within the We have checked the results obtained by apply- range found for a large number of studies, table 8, mg factors from table 13 to data in 108 digestion p. 12. This individual was also in negative bal- expenments which provided information on com- ance, excreting 26.4 grams of nitrogen in the 2-day position of the foods in the diet and data on bomb period during which he absorbed only 21.8 grams. calonmeter determinations of the food and feces. However, the errors involved are insignificant Although the experimental data needed for using when considered in terms of total available energy. every factor in table 13 were not provided by these 44 experiments, most of the factors could be tested when applied in various diets containing foods in this way. The available energy calculated by of both animal and plant sources either as mixed applying the appropriate energy factors to the diets or simple diets of two or more foods. composition data for the various foods was in excel- 2. That the factors are equally suitable when lent agreement with the comparable values for the applied to foods in diets in which various plant diets obtained by direct determinations of foods foods are predominant, as in fruit and nut diets, and feces and calculated urinary calories. The diets in which large amounts of beans or peas differences between the determined and calcu- are eaten, and diets in which large proportions lated values, not taking direction into account, of the calories are supplied by rice, wheat, or ranged from 0 to 5 percent and averaged 2 percent. vegetables. The calculated values were in some cases higher 3. That the factors applied to the several diets and in some lower than the determined values. of single foods give results in good agreement These positive and negative deviations were noted with the determined values for available energy. even in experiments in which the sam.e type of This indicates that the factors are applicable to diet and the same subject were used and suggest foods used alone in the diet, but further confir- that the differences may be in part the result of mation with additional data is needed. experimental error. 4. That the level of protein fed apparently The digestion experiments that were used to does not affect the extent of agreement obtained make this comparison include many types of diets: in estimating available energy by use of the Ordinary mixed diets with foods of animal and factors. This was indicated particularly in the plant origin; mixed diets containing large amounts group of experiments in which fruit and nuts of legum.es; diets of fruits and nuts; very simple made up a large part of the diet and the daily diets such as combinations of meat and bread, protein intake ranged from as low as 14 grams eggs, milk, and bread, whole-wheat bread and to a maximum of 85 grams; there was no evi- milk, bread m.ade of lower extractions of wheat dence of difference in the percentage deviations flour and milk, oatmeal and milk, or crackers and between calculated and determined values at milk; other simple diets containing large amounts the different levels of protein intake. of rice, dry peas, vegetables, or fruit; and a few The energy values of the 108 diets were calcu- diets of single foods. The proportions of protein, lated also by appl}âng the general factors, 4, 9, 4. fat, and carbohydrate in the food intake as well There were larger differences between the direct as the level of protein intake varied widely, the determinations and calculated values than were latter ranging from 14 to 184 grams daily. We observed when the values were calculated by use have grouped som.e of the diets and summarized of the factors from table 13. The largest differ- the diñerences we foimd between determined and ences were noted in those diets in which foods of calculated values as follows: plant origin predominated. In 14 diets of fruits and nuts the absolute Data have been summarized in table 19 from a deviation (that is, not taking signs into account) few of the experiments selected to represent differ- ranged from. 0 to 5 percent, averaging 2 percent. ent t3^pes of diets. The data illustrate the extent In 16 diets containing large quantities of diy of agreement between available calories directly beans, peas, or cowpeas the absolute deviation determined and those calculated by use of the ranged from. 1 to 5 percent, averaging 2 percent. factors from table 13 and by use of the general In 7 diets containing a large proportion of factors 4, 9, 4. Although there is good agreement rice or oatm.eal the absolute values deviated by between the determined and the calculated avail- only 1 percent in all cases. able energy values as illustrated by the data in In 6 diets of whole-wheat bread and m.ük the table 19, examination of the data show that for absolute deviations ranged from 2 to 4 percent, some kinds of diets similar agreement for the averaging 2.5 percent. available energy value of specific nutrients does In 11 diets containing a large proportion of not necessarily follow. For example, in the case cabbage, potatoes, beets, green corn, or apple- of experiment 388 which represents a diet low in sauce, the absolute deviations ranged from 0 to protein and fat, the apparent digestibility of the 3 percent, averaging 1 percent. total protein from the diet was 45 percent, with an In 6 ordinary mixed diets the absolute devia- estimated 25 calories available from proteiQ in- tions ranged from 0 to 3 percent, averaging 1.5 stead of the 46 which would be calculated by the percent. factors from table 13. Likewise, an estimated In 36 simple diets in which lower extractions 146 calories would be available from fat if the of wheat flours were fed as bread or crackers calculation were based on the apparent digesti- the absolute deviations ranged from 0 to 5 per- bility for the total fat in the diet, instead of the cent, averaging 2.5 percent. 201 obtained by use of the factors with the indi- vidual foods. For carbohydrate, however, the Several general observations appear reasonable data from this experiment would indicate approx- in view of these data: imately 861 available calories instead of the 823 1. That the energy factorsjn table 13 give an obtained by appUcation of the factors from table accurate estimation of thej^available energy 13 to the carbohydrate of the items in the diet.

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For the items in the diet and the very low level of example, the general factors overestimate the protein and fat. This example is useful, therefore, energy value of whole wheat by 22 calories per to point out that although the calorie factors in 100 grams, and a ton therefore would supply some table 13 are satisfactory for calculating total 200,000 fewer calories than calculated. To supply available calories in a diet of widely different the higher number of calories, estunated, however, composition and character from the ordinary 2,132 pounds instead of 2,000 would be needed. mixed diet, under some conditions there may be considerable error in calculating available calories Application of general factors to from specific nutrients. Caution should be used also in applying general digestibility coefficients to national food supplies such diets with a view to obtaining data on avail- able nutrients. Although general factors 4, 9, 4 may not be suit- able for estimating available energy values for indi- vidual foods, the question arises as to whether they General factors and more specific factors may be suitable for calculating calories of present- for calculating calories in individual foods day food supplies. Food consumption patterns have changed over the years (182), There have been When the factors shown in table 13 are applied major shifts in consumption of foods within groups to individual foods and the resulting calories and between groups. As a result there has been compared with calories obtained by use of the some shift in the proportions of protein, fat, and general factors 4, 9, 4, very large differences are carbohydrate supplied by the different foods observed for some foods. A fist of foods repre- within a group, and also a shift in the proportions sentative of different groups has been assembled of these nutrients from the various food groups in below in tabular form to illustrate this difference: the national food supply. We have grouped the foods into a few large Energy value per 100 categories and have calculated average coefficients grams edible portion derived by use of— of digestibility and calorie factors for the protein, Eatio fat, and carbohydrate of each of these groups. Food col, b Specific General fac- col. a For this we weighted data selected from table 13 factors tors 4, 9, 4 by the amount of the nutrient each food in the group supplied. These food group averages are (a) (b) shown in table 20. The average or general calorie factors for the total food supply also weighted Animal foods: Calories Calories Percent Beef 273 268 98 by current distribution data on nutrients were Salmon, canned 143 138 97 found to be 4.00, 8.92, and 3.97 calories per gram Eggs 162 158 98 as shoA\ai in table 20. These factors if rounded to Mük 68 69 101 Fats: simple whole numbers are the same as the general Butter 716 733 102 factors that have been used nearly 50 years. No Vegetable fats and oils. 884 900 102 large error is introduced in the calculation of Cereals: national per capita figures per day if general Cornmeal, whole ground (unbolted) 355 367 103 factors rounded to whole numbers are used instead Cornmeal, degermed 363 356 98 of the imrounded 4.00, 8.92, and 3.97. The net Oatmeal 390 396 102 result of applying these rounded factors to the Rice, brown 360 356 99 amounts of protein, fat, and carbohydrate of the Rice, white or milled-_. 362 351 97 Wheat flour, whole food suppl}^ would be to overestimate the total wheat 333 355 107 available calories from about one-half to less than Wheat flour, patent 364 355 1 percent. On a 3,000-calorie diet this would be Legumes: less than 30 calories. Beans, dry seeds 338 346 102 Peas, dry seeds 339 349 103 General factors such as these provide a quick Vegetables: means of calculatmg the physiological fuel value Beans, snap 35 42 120 from composition data of the total food supply Cabbage 24 29 120 in this country. They may be used with family Carrots 42 45 107 Potatoes 83 85 102 or institutional diets also if the pattern is compara- Turnips 32 35 109 ble in the types and proportions of food to those Fruits: used in this country. However, for limited or Apples, raw 58 64 110 unusual diets such as are found in some areas or Lemons, raw 32 44 138 Peaches, canned 68 75 110 for food supphes of totally different composition, Sugar: these general factors might not be suitable. Data Cane or beet 385 398 103 in table 21 illustrate the differences that may result from applying the rounded general factors

48 TABLE 20.- -Factors for digestibility, heats oj combustion, and physiological fuel values of nutrients in food groups as used in present-day mixed diets ^

Protein Fat Carbohydrate

Propor- Propor- Propor- Classes of food materials tion of Appar- Heat of Physio- Appar- Physio- Appar- ent combus- logical tion of ent Heat of tion of Heat of Physio- total in total in combus- logical total in ent logical mixed digesti- tion less fuel digesti- fuel digesti- combus- bility 1.25 2 value mixed bility tion mixed tion fuel diet diet value diet bility value

Percent Percent Caî.jgm. Cal.jgm. Percent Percent CaJ.lgm. Cal.lgm. Percent Percent Cal.lgm. Cal.lgm. Meats, fish, poultry 31 97 4.40 4. 27 36 95 9. 50 9.02 Eggs 7 97 4.50 4. 36 4 95 9.50 9. 02 Dairy products 25 97 4.40 4. 27 18 95 9. 25 8. 79 8 98 ~3~9b~ "3."87 Separated fats 19 95 9. 40 8.93

Total food of animal origin 63 97 4.41 4.28 77 95 9. 42 8.95 8 98 3.95 3. 87 Cereals, _ _ _ 23 86 4. 55 3.91 2 90 9. 30 8. 37 40 98 4. 20 4. 12 Legumes and nuts __ __ 6 78 4. 45 3. 47 3 90 9.30 8.37 3 97 4. 20 4. 07 Vegetables 6 70 3,75 2. 62 1 90 9.30 8. 37 9 93 4. 19 3. 90 Fruits, ______2 85 3.95 3.36 1 90 9. 30 8.37 8 90 4. 00 3.60 Sugars and sirups 32 98 3. 95 3.87 Separated fats and oils 16 95 9. 30 8. 84

Total food of plant origin 37 82 4.37 3. 58 23 94 9.30 8. 74 92 97 4. 10 3. 98 Total food 100 91 4. 40 4. 00 100 95 9. 39 8. 92 100 97 4.09 3.97

1 Based on United States of America food consump- 2 Heat of combustion corrected for incompletely oxidized tion data, 1949 (182). products in the urine.

4, 9, 4 and the specific factors for individual foods those used in developing the general factors. or food groups to different kinds of diets. Diet In the case of Diet B, which is also a mixed diet A may be considered comparable to that used but one in which the proportions of different t3rpes currently in this country. It has fairly large of food are very difi'erent, calories calculated by quantities of meat, milk, fats, and sugar, and the use of the general and specific factors are not relatively small quantities of cereals; the greater in as good agreement. proportion of the cereals are refined products. General factors may therefore be used for esti- Diet B, on the other hand, follows the dietary mating the energy value of average family diets pattern of some of the Eastern European countries or of the national food supply of this country and has very high proportions of unrefined cereals from the total quantity of protein, fat, and carbo- and potatoes and relatively small amounts of meat, hydrate. The more specific factors should be fat, eggs, and sugar. used for most other calculations, such as those for Results of applying the general and specific factors ia this example show that for Diet A experimental and therapeutic diets, individual either set of factors would be satisfactory. No foods, food supplies of a totally different character significant error is to be expected from applying from that of this country, and particularly for general factors in this case because the proportions areas of the world where the food supplies consist of the different types of food are the same as largely of unrefined cereals and vegetables.

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50 CONCLUSIONS

It is recognized that some of the physiological tions existent in the basic data, nevertheless when fuel factors for food groups and individual foods they were applied to the nutrients in foods fed developed as shown in this publication and alone or m various combinations, the estimated summarized in table 13 are based on a limited total available energy of the food was always amount of data and that factors for food groups in excellent agreement with the value determined may not always be equally suitable for individual by use of the bomb calorimeter. foods within the group. Also revisions are antici- In view of the agreement noted and until more pated as more complete information becomes basic information becomes available, the modifica- available on the various constituents in the tion of the method of Atwater and Bryant as pro- nitrogenous matter, fat and carbohydrate oí food, and on their heats of combustion and posed in the present publication for estimating digestibilities. Moreover it is realized that there the available (or physiological) energy value of are problems mth direct bearing on the digesti- foods seems the most satisfactory procedure to bilit}^ of protein, fat, and carbohydrate that have use; the calorie factors presented in table 13 not been resolved satisfactorily at this time. are recommended for calculating the total available Although all of the calorie factors may not be energy value of foods until there is basis for further entirely suitable as a result of the various limita- revision or refinement of the factors.

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CANNA, CASSAVA, TARO, TREE-FERN, AND Res. 12: 118-121 POTATO STARCHES. Jour. Biol. Chem. (110) MACRAE, T. F., HUTCHINSON, J. C. D., IRWIN, J. 0., 52: 251-261. and others. (93) and HOLMES, A. D. 1942. COMPARATIVE DIGESTIBILITY OF WHOLE- 1916. STUDIES ON THE DIGESTIBILITY OF THE MEAL AND WHITE BREADS AND THE GRAIN SORGHUMS. U. S. Dept. Agr. EFFECT OF THE DEGREE OF FINENESS OF Bui. 470, 30 pp. GRINDING ON THE FORMER. Jour. Hyg. (94) and HOLMES, A. D. 42: 423-435. 1917. EXPERIMENTS IN THE DETERMINATION OP (111) MACY, I. G. THE DIGESTIBILITY OF MILLETS. U. S. 1942. NUTRITION AND CHEMICAL GROWTH IN Dept. Agr. Bui. 525, 11 pp. CHILDHOOD, VOL. I. EVALUATION. (95) and HOLMES, A. D. Springfield, 111. and Baltimore, Md. 1917. THE DIGESTIBILITY OF THE DASHEEN. U. S. (112) Dept. Agr. Bui. 612, 12 pp. [1946.] NUTRITION AND CHEMICAL GROWTH IN (96) and HOLMES, A. D. CHILDHOOD. VOL. II. ORIGINAL DATA. 1921. THE EFFECT OF A VARIATION IN MILLING Springfield, 111. ON THE DIGESTIBILITY OF WHEAT (113) MALFATTI, H. FLOURS. Nati. Acad. Sei. Proe. 7: 1884. üBER DIE AUSNUTZUNG EINIGER NAHR- 119-123. UNGSMITTEL IM DARMCANAL DES MEN- (97) and MERRILL, A. T. SCHEN. K. Akad. der Wiss. Sitzber. 1924. DIGESTIBILITY OP RAW STARCHES AND [Vienna] 90: 323-350. CARBOHYDRATES. U. S. Dept. Agr. (114) MAYNARD, L. A. Bul. 1213, 16 pp. 1944. THE ATWATER SYSTEM OF CALCULATING (98) and MiLNER, R. D. THE CALORIC VALUE OF DIETS. JOUT. 1904. INVESTIGATIONS ON THE NUTRITION OF Nutr. 28: 443-452. MAN IN THE UNITED STATES. U. S. (115) Off. Expt. Stas. Doc. 713, 20 pp., illus. 19^6. INTERNATIONAL FOOD-EVALUATION ACTIVI- (99) LEHMANN, K. B. TIES AND PROBLEMS. Fed. Proc. 5; 270- 1902. HYGIENISCHE UNTERSUCHUNGEN üBER 273 MEHL UND BROT. XI. TJBER DIE BEDEU- (116) MENDEL, L. B. TUNG DER SCHäLUNG UND ZERMAHLUNG 1898. THE CHEMICAL COMPOSITION AND NUTRI- DES GETREIDES FüR DIE AUSNUTZUNG TIVE VALUE OF SOME EDIBLE AMERICAN (AVEDYK- UND STEINMETZVERFAHREN). FUNGI. Amer. Jour. Physiol. 1: [225]- Arch. f. Hyg. 45: 177-211. 238. (100) LEUNG, W. W., PECOT, R. K., and WATT, B. K. (117) and FINE, M. S. 1952. COMPOSITION OF FOODS USED IN FAR 1912. STUDIES IN NUTRITION. IV. THE UTILI- EASTERN COUNTRIES. U. S. Dept. Agr. ZATION OP THE PROTEINS OF THE Handb. 34, 62 pp. LEGUMES. Jour. Biol. Chem. 10: (101) LusK, G. 438-458. 1928. THE ELEMENTS OF THE "SCIENCE OF NUTRI- (118) MERRILL, A. L., and WATT, B. K. TION. Ed. 4, 844 pp., illus. Phila- 1948. PHYSIOLOGIC ENERGY VALUES OF WHEAT. delphia and London. Amer. Dietet. Assoc. Jour. 24: 953-956. (102) MCCANCE, R. A., and GLASER, E. M. (119) MERRILL, L. H. 1948. THE ENERGY VALUE OF OATMEAL AND THE 1905. CEREAL FOODS. Maine Agr. Expt. Sta. DIGESTIBILITY AND ABSORPTION OF ITS Bui. 118, pp. [1171-135. PROTEINS, FATS AND CALCIUM. Brit. (120) Jour. Nutr. 2: 221-228. 1906. INDIAN CORN AS FOOD FOR MAN. DI- (103) and LAWRENCE, R. D. GESTION EXPERIMENTS WITH CHEST- 1929. THE CARBOHYDRATE CONTENT OF FOODS. NUTS. Maine Agr. Expt. Sta. Bui. 131: Brit. Med. Res. Council Spec. Rpt. [133]-148. Ser., No. 135, 73 pp. London. (121) (104) and WALSHAM, C. M. 1908. FOOD OF MAN STUDIES. Maine Agr Expt. 1948. THE DIGESTIBILITY AND ABSORPTION OF Sta. Bui. 158, pp. [219]-238. THE CALORIES, PROTEINS, PURINES, FAT (122) MITCHELL, H. H., and CURZON, E. G. AND CALCIUM IN WHOLEMEAL WHEATEN 1940. THE FOOD VALUE OF ETHYL ALCOHOL. BREAD. Brit. Jour. Nutr. 2: 26-41, Quart. Jour, of Studies on Alcohol 1: illus. [227]-245. (105) and WiDDowsoN, E. M. (123) MORNBR, C. T. 1940. THE CHEMICAL COMPOSITION OF FOODS. Brit. Med. Res. Council Spec. Rpt. 1886. BEITRÄGE ZUR KENNTNISS DES NÄHR- Ser., No. 235, 150 pp. London. WERTHES EINIGER ESSBAREN PILZE. Ztschr. f. Physiol. Chem. 10: [503]-516

54 (124) MuRLiN, J. R., EDWARDS, L. E., HAWLEY, E. E., (138) PUGLTESE, A. and CLARK, L. C. 1915. LA VALEUR ALIMENTAIRE DES DIVICR8 1946, BIOLOGICAL VALUE OF PROTEINS IN RE- TYPES DE PAIN. Rev. Gén. des Sei. LATION TO THE ESSENTIAL AMINO Pures et Appl. 26: 612-617, illus. ACIDS WHICH THEY CONTAIN. I. THE (139) REMY, E. ENDOGENOUS NITROGEN OF MAN. JOUr. 1931. EXPERIMENTELLE STUDIEN ZUH BIOCHEMIE Nutr. 31: 533-554, illus. UND BIOLOGIE DER ROTTFASER. Bio- (125) EDWARDS, L. E., FRIED, S., and others. chem. Ztschr, 236: 1-18. 1946. BIOLOGICAL VALUE OF PROTEINS IN RELA- (140) PtICIITER, A. P. F. TION TO THE ESSENTIAL AMINO ACIDS 1903, ÜBER DIE AUSNÜTZUNG VON ERBSEN IM WHICH TPIEY CONTAIN. III. COM- DARMKANAL DES MENSCHEN BEI WEI- PARISON OF PROTEINS WITH MIXTURES CHEM UND HARTEM KOCH WASSER. Arch. OF THE AMINO ACIDS. Jour. Nutr. 31: f, Hyg. 46: 264-273. 715-736. (141) RoMBERG, E. (126) - LINE, W. R., PIPER, H. A., and PIERCE, H.B. 1897. DER NÄHRWERTH DER VERSCHIEDENEN 1929. THE NUTRITIVE VALUE OF CEREAL BREAK- MEHLSORTEN EINER MODERNEN ROGGEN- FAST FOODS. I. COMPOSITION AND KUNSTMÜHLE. Arch. f. Hvg. 28: [244]- HEAT VALUE. JouF. Nutr. 2: 83-90. 290. (127) MARSHALL, M. E., and KOCHAKIAN, C. D. (142) ROSE, M. S., and COOPER, L. F, 1941, DIGESTIBILITY AND BIOLOGICAL VALUE OF 1917, THE BIOLOGICAL EFFICIENCY OF POTATO WHOLE WHEAT BREADS AS COMPARED NITROGENS Jour. Biol. Chem. 30: 201- WITH WHITE BREAD. Jour. Nutr. 22: 204. 573-588, illus. (143) and MACLEOD, G. (128) and MATTILL, H. A. 1925. MAINTENANCE VALUES FOR THE PROTEINS 1938. DIGESTIBILITY AND NUTRITIONAL VALUE OF MILK, MEAT, BREAD AND MILK, AND OF CEREAL PROTEINS IN THE HUMAN SOY BKAN CURD. Jour. Biol. Chem. suB.iECT. Jour. Nutr. 16: 15-35. 66: 847-867. (129) NäSSET, E. S., and MARSH, M. E. (144) RUBNER, M. 1938. THE EGG-REPLACEMENT VALUE OP THE 1879. UEBER DIE AUSNUTZUNG EINIGER NAHR- PROTEINS OF CEREAL BREAKFAST FOODS, UNGSMITTEL IM DARMCANALE DES MEN- WITH A CONSIDERATION OF HEAT IN- SCHEN. 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THE UTILIZATION BY HUMAN SUBJECTS OP (153) SCHLESTNGER, H. THE NITROGEN, CALCIUM, AND PHOS- 1895. BEITRÄGE ZUR BEURTHEILUNG DES CACAOS PHORUS OF THE NAVY BEAN (PHASEOLUS BEI DER ERN^ÄHRUNG DES MENSCHEN. VULGARIS) WITH AND WITHOUT A SUP- Deut. Med. Wchnschr. 21: 80-82. PLEMENT OF CYSTINE. Jour. Nutr. (154) SCHOCH, T. J. 5: 277-294. 1938. ABSENCE OP COMBINED FATTY ACID IN (136) PLAGGE and LEBBIN. CEREAL STARCHES. (Communlcations 1897. UNTERSUCHUNGEN ÜBER DAS SOLDATEN- to the Editor) Amer. Chem. Soc. BROT. 234 pp., illus. Berlin. (Ver- Jour 60: 2824-2825. öffentlichungen aus dem Gebiete des (155) SEALOCK, R. R., BASINSKI, D. H., and MURLIN, J. R Militär-Sanitätswesens, Heft 12.) 1941. APPARENT DIGESTIBILITY OF CARBOHY- (137) PRAUSNITZ, W. DRATES, FATS, AND "INDIGESTIBLE RESI- 1890. DIE AUSNUTZUNG DER BOHNEN IM DARM- DUE" IN WHOLE WHEAT AND WHITE KANÄLE DES MENSCHEN. Ztschr. f. BREADS. Jour. Nutr. 22: 589-596, Biol. 26: 227-232. illus. 55 (156) SHERMAN, H. C. (173) STREET, H. 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Cereal Chem. Med. 17: [10S]-119. 18: 811-819, illus. (177) STUTZER, A. (161) SKINNER, J. T., PETERSON, W. H., and STEENBOCK, 1891. NEUES AUS DER ROST-, DARR- UND TROCK- H. NUNGS-INDUSTRIE. Ztschr. f. Angew. 1933. NÄHRWERT VON SCHIMMELPILZMYCEL. Chem. Jahrg. 1891, Heft. 12: 368-375. Biochem. Ztschr. 267: [169H78. (178) SUGIMOTO, K. (162) SNYDER, H. 1926. STUDIES ON THE DIGESTIBILITY AND 1897. THE DIGESTIBILITY OF POTATOES AND UTILISATION OF RICE OF DIFFERENT EGGS. In U. S. Dept. A^r. Off. Expt. GRADES OF POLISHING. lu Saiki, T., Stas. Bui. 43, Losses in Boiling Vege- [ed-l Progress of the Science of Nutri- tables and the Composition and Digesti- tion in Japan. League of Nations bility of Potatoes and Eggs, pp. 20-24. Health Organ. III. Health III. 25. (163) C. H. 523, pp. [871-154. 1899. MISCELLANEOUS ANALYSES: COMPOSITION (179) — HiGUCHi, M., MoMOYEDA, S., and others. OF TOMATOES. PROTEIDS OF WHEAT 1926. THE DIGESTIBILITY AND UTILISATION OF FLOUR. Minn. Agr. Expt. Sta. 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56 (188) WILLIAMS, R. T., éd. (192) WOOD, T. B. 1952. LiPiD METABOLISM. Bíochem. Soc. Sym- 1911. THE COMPOSITION AND FOOD VALUE OF posia 9, 101 pp. [London.] BREAD. Royal Agr. Soc. England Jour. (189) WlNTGBN, M. 72: 1—24. 1905. UBBER DIE AUSNUTZBARKEIT VON LEGUMI- NOSENMEHLEN. Vëroffentl. aus. dem (193) WOODS, C. D., and MERRILL, L. H. Gebiete des Mílit.—Sanitatsw. 29: 1900. A REPORT OF INVESTIGATIONS ON THE [37J-55. DIGESTIBILITY AND NUTRITIVE VALUE (190) WOLLAEGER, E. E., COMFORT, M. W., and OSTER- OF BREAD. U. S . Dept. Agr. Off. Expt BERG, A. E. Stas. Bui. 85, 51 pp. 1947. TOTAL SOLIDS, FAT AND NITROGEN IN THE FECES: III. A STUDY OF NORMAL PER- (194) - and MERRILL, L. H. SONS TAKING A TEST DIET CONTAINING 1904. ENTIRE WHEAT FLOUR. Maine Agr. Expt A MODERATE AMOUNT OF FAT; COM- Sta. Bui. 103, pp. [61]-76, illus. PARISON WITH RESULTS OBTAINED WITH NORMAL PERSONS TAKING A TEST DIET (195) ■ and MERRILL, L. H. CONTAINING A LARGE AMOUNT OF FAT. 1904. STUDIES ON THE DIGESTIBILITY AND Gastroenterol. 9: 272-283. NUTRITIVE VALUE OF BREAD AT THE (191) LuNDBERG, W. 0., CHIPAULT, J. R., and MAINE AGRICULTURAL EXPERIMENT STA- MASON, H. L. TION 1899-1903. U. S. Dept. Agr. Off. 1953. FECAL AND PLASMA LIPIDS. A STUDY OF 2 Expt. Stas. Bui. 143, 77 pp. NORMAL HUMAN SUBJECTS TAKING (L) A DIET FREE OF LIPID AND ^2) A DIET (196) and SNYDER, H. CONTAINING TRIOLEIN AS THE ONLY 1906. CEREAL BREAKFAST FOODS. U. S. Dept. LIPID. Gastroenterol. 24: 422-436. Agr. Farmers' Bui. 249, 36 pp.

57 APPENDIX. TABULAR SUMMARY OF EXPERIMENTS ON DIGESTI- BILITY OF FOODS OF PLANT ORIGIN BY HUMAN SUBJECTS

Apparent Digestibility and Available Energy Apparent digestibility.—The coefficients of digestibility Scope of compilation.—The compilation of human di- gestion experiments given in table 23 presents data on the reported in the table represent apparent digestibility In apparent digestibility of protein, fat, carbohydrate, and calculating the apparent digestibility no attempt has been energy, and in some cases the availability of the total made to distinguish between metabolic products and un- energv of various foods of plant origin. It covers research digested food in the feces. Using protein as an example, in this field since 1875. Data published in languages other these coefficients are calculated as follows: than Enghsh may not have been covered completely but the Protein in- Protein (from greater portion 'is believed to have been reviewed. The take from— test food) in Coefficient of apparent reports included in the compilation may be identified by test food ÎË^Ë^_^ XI00=digestibility of protein the numbers in the last column of the table, which refer Protein intake from test food of test food as percent. to Literature Cited, page 51. Coefficients of apparent digestibihty of fat are shown m Where there were no data on the basal diet and the diets the table, but in many cases are not considered to be reli- used were relatively simple, the fecal protein for the diet able. With the exception of a few kinds of plant foods, exclusive of the test food was calculated from the coeffi- such as nuts, the fat content is too low to contribute more cient of digestibilitv of the various items m the diet. i;or than a small part of the total fat intake. Thus, in calcu- example, in a very^simple diet of bread and milk in which lating the digestibihty of the fat of the test food even a bread was the test food, it was commonly assumed that small error in the assumptions made for digestibility of milk protein would have a digestibility of 97 percent. fat of the remainder of the diet may result in a relatively Then the fecal protein from milk would be 3 percent oí the large error in the estimated digestibility of the test food. milk protein intake (100-97) and that from bread would Too much importance should not be given to the re- be the difference between the total fecal protein and the ported figures for gain or loss of body nitrogen in studies milk fecal protein. . in which the experimental periods were short and in When the authors determined the digestibihty ot a mixed studies in which no preliminary period on the experimental diet during a preliminary period and then substituted the diet was indicated. If the period on the experimental test food for a specified proportion of the mixed diet, it was diet had been sufiSciently long the subjects might have assumed that reducing the intake of the basal diet did not reached nitrogen equilibrium. change its digestibility. If the test food replaced 15 per- This compilation includes studies in which the apparent cent of the basal diet, the fecal protein in the test period digestibility of the test food was reported or could be cal- due to the basal diet was considered to be 85 percent of the culated from data given by the author. A wide variety of fecal protein found experimentally for the basal period. experimental conditions are represented, some of which The resulting value was subtracted from the total fecal were too extreme for derivation of coefiicients of digesti- protein in the test period to obtain the protein from the bility for general use as represented in table 13. However, test food in the feces. they are useful in considering the effects that various con- The coefficients of digestibility of fat, carbohydrate, and ditions of dietary intake and experimental procedures may of energy have been calculated in the same way. have upon the digestibility of foods and for this reason The proportion of gross energy available to the body was are included in the compilation. reported in a limited number of studies. To obtain this Order of foods.—^The order in which the food groups value the energy lost in the urine, as well as the energy appear in the table follows that used by Atwater and value of the feces, was deducted from the gross energy of Bryant in their report of 1899 (17) and by the Food and the food intake. The absorbed fat and carbohydrate were Agriculture Organization ad hoc Committee in its report considered to be completely oxidized, and the unoxidized of May 1947 (65). This order seemed desirable in that organic matter of the urine was assumed to be mainly the first two groups, "Grain, Grain Products" and ''Le- nitrogenous products. The energy loss in the urine was gumes and Nuts," are both important sources of calories, assumed to average 1.25 calories per gram of absorbed and it is on foods in these two groups the greater portion of protein. On these assumptions the available energy of the the research on digestibility of foods of plant origin has test food was calculated as follows: been done. The food items within each group have been arranged Gross energy of test food—fecal energy from test alphabetically except where some other arrangement is food—energy löst in urine (digestible protein from test believed to be more useful to the reader. For example, the foodX 1.25) = available energy from test food. wheat items are in the order of their relation to the original grain, starting with the items most similar to the whole Available energyX100^Percent of gross energy available grain in composition and form. Thus, the whole-grain Gross energy to the body. flours appear first, followed by intermediate extractions, 80-percent extraction and lower extractions. Table 22 shows in detail the results of calculations for The common plant names in table 23 are followed by estimating the coefficients of digestibility of protein, fat, their scientific names to aid the user in identification of carbohydrate, and energy, and the proportion of energy items. Occasionally the scientific names were given by actually available to the body. This experiment was taken the authors (items 23, 24, 88-91, 316-320). Otherwise we from one of the early reports of Snyder (164). -* have used the ones preferred in Standardized Plant Names Adaptations of published data.—All the studies in which {79) with a few exceptions where other names were recom- original basic data were reported by the authors have been mended by the Horticultural Crops Research Branch of recalculated prior to inclusion in table 23. Differences, the Agricultural Research Service, U. S. Department of when found, between the results as originally reported and Agriculture. the recalculated figures were of three types:

58 1. Whereas in most studies investigators assumed di- 2. In some studies the authors did not report apparent gestibility coefficients for the basal foods close to or the digestibihty or available energy but reported the basic same as those shown in table 13, in occasional studies data needed for making such calculations. For these they applied other coefficients of digestibility. As a re- cases we have calculated the values entered in table 23 sult, the original figures for digestibihty and proportion as noted in a footnote. of energy available from the test food were in some cases 3. In still other experiments when we used the basic considerably different from results we obtained by apply- data and assumptions reported by the authors in calcula- ing the usual coefficients to the basal diets. If our recal- tion, we obtained a different result. Our recalculated culated figures differed from the reported results by more values have been entered in brackets in talkie 23- than 1 percent, they were entered in table 23, and atten- tion called to this change by a footnote.

TABLE 22.—Use of digestibility data to determine coefficients of apparent digestibility and available energy

Sample Weight of Protein Fat Carbo- Heat of No. material (Nx6.25) hydrate Ash combustion

Food consumed: Grams Grams Grams Grams Grams Calories 70 Bread (made from graham flour) _ _ _ 908. 3 70. 5 11. 5 389. 0 8.6 2 093 69 Milk 3, 250. 0 95.9 113.8 167.4 25.7 2 ' 327 Total ___ 166. 4 125.3 556.4 34.3 4, 420 71 Feces (water free) _ _ 90. 0 16.3 9. 4 49. 6 14. 7 392 Estimated feces from food other than bread 2.9 5.7 3.3 83 Estimated feces from bread _ _ 13.4 3. 7 46. 3 309 Total amount digested 150. 1 115. 9 506. 8 19.6 4,028 Estimated digestible nutrients in bread _ 57. 1 7. 8 342. 7 1,784 Percent Percent Percent Percent Percent Coefficients of digestibility of total food _ 90.2 92.5 91. 1 57. 1 91. 1 Estimated coefficients of digestibility of bread _ 81.0 67. 8 88. 1 85.2 Proportion of energy actually available to body: In total food 86.9 In bread alone ______81. 8

NOTE.—This table appears as table 18 in U. S. Department of Agriculture Bui. 101 {164)-

Terms and symbols used.-—^References to "authors" in authors' description. To illustrate, for item 9 the term either the footnotes or descriptive columns in table 23 "hominy" was not used in the text of the article but since apply to the authors of the specific digestibility reports and there was little doubt as to the identity of the product this not to the compilers of table 23. interpretation of the test food was noted in parenthesis in The proportion of protein, fat, carbohydrate, and energy addition to the author's description of the product. supplied by the test food in the diet has been shown in the Quotation marks have been used with certain food items table wherever suitable information on composition and to indicate that they were quoted directly from the article. amounts of food were reported. In some cases composi- This was done whenever a term might have different con- tion data given were not complete and we have used notations. For example, entire-wheat flour, as used in figures from Agriculture Handbook No. 8 (185) to supply studies reported in the early part of the 20th century, was missing composition data and have entered the results in a flour of intermediate extraction having part of the bran parentheses in table 23. removed. Today this term applies to a whole-grain Parentheses were used also in the descriptive columns product. for added explanatory phrases as interpreted from the

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99 Composition and Heat of Combustion of Foods

Composition and heat of combustion data are recorded For ease in using the data the test foods with composition in table 24 for test foods used in digestion experiments reported carry the same item number in both tables 23 described in table 23 whenever such data were reported. and 24. The composition data are recorded as reported Composition data are useful in identification of a food item by the authors and the factors they used for converting and in interpretation of experimental results in digestion nitrogen to protein are noted in footnotes. More complete experiments in which that item is used. description of the food items is given in table 23.

TABLE 24.—Composition and heat of combustion oj food items used in experiments on human digestibility (table 23)

Carbohydrate Heat of Test food, description Protein Fat Ash combus- Ref. No. Total (by tion per difference) Fiber gram

GRAINS, GRAIN PRODUCTS Barley Products {Hordeum vulgäre) : Percent Percent Percent Percent Percent Percent Calories 1 Barley, flaked 9.79 18.87 1.24 79.22 0. 77 0. 88 62 2 Barley, germinated, flaked 10. 18 1 10. 62 1.21 76.89 1.27 1. 10 62 Buckwheat Products {Fagopyrum escu- lentum) : 5 Flour 11. 34 2 8. 13 1.22 77. 69 1.62 134 Corn, Corn Products {Zea mays): 8 Hominy 10.96 *9. 44 .67 78. 61 .37 .32 3.986 120 9 (Hominy) hulled using alkali, steamed 0 2 9. 96 5. 30 76. 77 1. 51 7. 97 4. 440 121 0 2 8. 92 5.00 77. 96 .69 8. 12 4. 164 0 5 10. 05 5. 65 76. 67 .78 7.63 4. 625 11 Meal 9.52 1 6. 87 . 65 82.67 .46 .29 62 14 Meal, granulated: a 11. 79 *8. 50 . 98 78. 25 .46 .48 3. 823 120 b 7.77 *8. 69 1. 92 81. 12 .40 .50 4.023 15 Meal, waxy variety of maize im- ported from China 10. 54 *8. 88 4.24 75.04 1.67 1.3 G7 16 Meal, white 9. 88 *10. 63 6. 17 71. 52 1. 83 1. 80 97 20 Corn endosperm, toasted, added sugar and salt 7.49 2 7. 38 1. 68 80.38 3.07 3. 869 126 Oats, Oat Products {Avena sativa) : 25 Rolled oats 8.66 2 14. 69 6.96 67. 89 1. 80 4. 560 164 27 Rolled oats 11. 02 2 15. 69 7.23 64. 23 1. 83 126 28 Rolled oats 7.90 3 15. 10 88 32 Rolled oats, quick-cooking 7. 36 2 16. 13 6. 14 68. 53 .90 1. 84 129 33 Meal, granulated or pinhead 7.51 1 12. 43 6. 31 72.23 1. 94 1. 52 62 34 Meal 7.35 1 13. 17 7. 53 70. 23 1. 04 1.72 62 35 Meal, rolled 7.45 1 12. 21 7. 27 71. 37 1. 15 1. 70 62 36 Meal 8. 12 1 13. 25 7.28 69.57 1. 12 1.78 62 38 Meal: a. Coarsely ground pinhead 15. 3 11. 70 7.21 64.47 .85 1. 62 102 b. Medium ground 15. 3 8. 60 7. 78 67. 15 .93 1.47 Average 15. 10. 10 7.50 65. 86 .89 1. 54 Rice, Rice Products {Oryza sativa) : 49 Polished or white (12. 92) *8. 55 .31 77. 89 .33 Undescribed 3.854 167 50 13.50 4 8. 27 . 3 77.26 .67 144 Rye, Rye Products {Sécale céréale) : 54 Flour No. 18 9.25 *15. 48 2.01 71.08 2. 18 141 55 Flour III, a comercial flour 11.40 *14. 92 1.89 69. 82 141 56 Flour No. 17 1.97 10. 96 *15. 78 1. 89 69.47 1.90 141 57 Flour No. 4 9.30 *15. 67 1.78 71.38 58 Flour No. 16 1.87 141 10. 06 *16. 14 1.76 70. 30 1. 74 141 59 Flour No. 15 11.00 *15. 38 1.71 70. 22 60 Flour II 1.69 141 11.26 *15. 33 1.89 69. 84 1. 68 141 ' N X 5.7. ^ N X 5.95. 2 N X 6.25. *N-conversion factor not reported. 3 N X 5.83.

TOO TABLE 24.—Composition and heat of combustion of food items used in experiments on human digestibility {table ^5)—Continued

Carbohydrate Heat of Test food, description Water Protein Fat combus- Ref. No. Total (by tion per difference) Fiber gram

GRAINS, GRAIN PRODUCTS—Con. Rye, Rye Products {Sécale céréale)—Con. 61 Flour, whole grain, most external Percent Percent Percent Percent Percent Percent Calories layer removed 13.0 3 (8. 40) ' (2. 03) 1. 52 (Whole-grain Swiss rye before pro- cessing) Ö (13.0) 3 (8.28) « (1.65) (1-61) 64 Flour, flours No. 6 and No. 18 blended in equal amounts 9. 16 *12. 42 1.30 75. 72 1.40 65 Flour, finely ground flour com- monly used in Wurzburg 11.6 3 9.33 1.24 66 Flour, flours 0 and III blended in equal amounts 11.32 *10. 76 1.38 75.34 1. 20 71 Flour, made by Steinmetz process from rye of Silesia (13.0) 3 (9. 62) « (1.57) (1.18) (Whole-grain rye of Silesia before processing) 7 13.0 3 (9.21) 5 (2. 71) (1.84) 72 Flour, made by **old process" of milling from Swiss rye (13.0) M7. 11) 5 (. 66) (1.10) 73 Flour No. 13 11. 19 *11. 85 1. 14 74.78 1.04 74 Flour No. 12 11. 56 *11. 42 1. 69 74.37 .96 75 Flour, 75 percent yield 14.73 3 9.79 .86 77- Flour I 11.84 *10. 22 1.00 76. 13 .81 78 Flour No. 10 11.76 *10. 81 . 97 75. 69 . 77 79 Flour No. 2 12. 14 *9. 80 .73 76. 60 . 73 80 Flour No. 7 11. 87 *9. 31 . 78 77. 42 . 62 81 Flour No. 6 9.07 *9. 35 .59 80. 37 .62 82 Flour, 62 percent yield (13.0) 3 (8. 69) (-67) (.55) 83 Flour 0 11. 25 *6. 59 80.85 .43 84 Flour No. 1 12.49 *5. 36 . 59 81. 17 .39 85 Branny portion, fraction of 67-85 percent ^ 14. 8 *20. 2 3.3 58.9 2.9 2.8 86 Branny portion, fraction of 67-95 percent ^ 14.8 *18. 5 3.4 59.6 4.6 3.7 87 Branny portion, fraction of 85-95 percent ^ 14. 2 *16. 2 3.6 61. 1 7.5 4. 9 Wheat, Wheat Products (Triticum aesti- vum): Flours, whole grain and nearly whole grain: 92 Graham, 100-percent extraction, Scotch Fife, hard spring 8. 61 1 12. 65 2.44 74. 58 72 148 (Whole grain before processing)» 8.50 1 12. 65 2.36 74.69 80 140 93 Graham, 100-percent extraction, Scotch Fife 13.21 1 14. 21 2.01 68.56 2.01 3.971 (Whole grain before processing) io__- 10.41 1 15. 50 2.28 69. 88 1. 93 4.023 94 Graham, 100-percent extraction 10.51 2 14. 00 2.52 70.97 2.00 4.004 96 Graham, milled from Oregon white 8. 15 1 8. 18 1. 68 80. 27 1. 72 3. 990 winter wheat 4.008 (Whole grain before processing) ^i— 8.99 1 8. 32 1.83 79. 10 1. 76 97 Graham, milled from hard winter Weissenburg wheat from Okla- 4. 178 homa 7.73 1 15. 33 1. 79 73. 83 1. 32 (Whole grain before processing)'2__ 8. 65 1 15. 33 1. 83 72.87 1.32 4. 110 98 Graham, milled from Michigan soft 3.906 winter wheat 11.23 1 12. 24 1.41 73.27 1.85 (Whole grain before processing) ^3- 10.25 1 12. 34 1. 35 74. 23 1.83 4.000 102 Graham 11.82 *10. 63 1. 71 74. 12 2.25 1.72 1 N X 5.7. from this sample. Also from this wheat were prepared 2 N X 6.25. items No. 94, 114, and 137 appearing in another report. ' N X 5.83. 10 Items No. 93, 113, and 136 were prepared from tnis 5 Reported as cellulose. ' Items No. 61 and 72 were prepared from this sample. ^^^ R^ems No. 96 and 115 were prepared from this sample ' Items No. 71 and 82 were prepared from this sample. 12 Items No. 97, 116, 139, 173 and 174 were prepared 8 The rye was milled to 67 percent and the branny frac- from this sample. . , ... tion obtamed from the remaining portion. Refers to 13 Items No. 98, 118, and 141 were prepared from this original grain with 5 percent loss from cleaning. sample. ^ Items No. 92, 112, 135, 146, and 147 were prepared *N-conversion factor not reported.

101 TABLE 24.—Composition and heat of combustion oj food items used in experiments on human digestibility {table ;^5)—Continued

Carbohydrate Heat of Test food, description Water Protein Fat combus- Ref. No. Total (by tion per diflerence) Fiber gram

GRAINS, GRAIN PRODUCTS—Con. Wheat, Wheat Products {Triticum aesti- vum)—Continued Flours, whole grain and nearly whole grain—Continued 106 Whole meal, milled from Canadian Percent Percevt Percent Percent Percent Percent Calories wheat 15. 3 15. 40 2.23 (14) 2.36 104 107 Whole meal, milled from English wheat 15. 3 8. 52 1.83 (15) 2.02 104 108 Whole meal 13. 50 3 11. 66 1.82 71.49 1.53 28 109 100 percent of wheat kernel 14. 38 2 10. 92 1.81 71.69 1.20 146 Flours, intermediate extractions: 112 '^Entire wheat" 10. 81 1 12. 26 2.24 73.67 1.02 4.032 164 113 ''Entire wheat" 13. 51 1 13. 72 1.69 70. 10 3.877 166 114 "Entire wheat" milled from hard spring wheat, Scotch Fife 10. 99 2 13. 00 2.28 72.51 1.22 3. 944 195 115 "Entire wheat" milled from Oregon white winter wheat 8. 66 17.52 1.67 81. 08 1.07 3.900 168 116 "Entire wheat" milled from hard winter Weissenburg wheat from Oklahoma 7. 46 1 15. 16 1.64 74.52 1. 22 4. 159 168 117 ' 'Entire wheat" milled from Indiana soft winter wheat 9. 60 1 12. 80 1.54 74.40 1.66 4.020 166 (Whole grain before processing) __ i« 8. 09 1 13. 16 1.52 75.38 1.85 4.090 118 "Entire wheat" milled from Michi- gan soft winter wheat 11.01 1 12. 01 1.53 74. 17 1.28 3. 860 166 123 90-percent extraction, milled from English wheat 15. Í 8.32 1. 15 106 124 90-percent extraction, milled from Manitoba wheat 15. 1 13. 51 1.15 106 131 80-percent extraction, milled from English wheat 15. 18. 15 . 17 106 132 80-percent extraction, milled from Manitoba wheat 15. 1 13. 05 .24 Flours, lower extractions: 106 135 Standard patent, milled from hard spring wheat, Scotch Fife 10. 54 1 11. 99 1.61 75.36 0.50 136 Straight patent, milled from hard 4.050 164 spring wheat, Scotch Fife 12. 38 1 13. 60 1.30 72.04 .68 137 Straight patent, milled from hard 3.861 166 spring wheat, Scotch Fife 11. 55 2 12. 75 1.43 73. 67 138 Standard patent, about 70 percent .60 3.889 195 yield, milled from Oregon white winter wheat 8. 94 16.90 1.25 82.47 139 Standard patent, about 70 percent .44 3.880 168 yield, milled from hard winter Weissenburg wheat from Okla- homa 9. 93 1 13. 74 .92 74. 89 140 Standard patent, milled from Indi- . 52 4. 040 168 ana soft winter wheat 10.30 1 12. 30 .93 75. 94 141 Standard patent, contained less .53 4. 010 166 than 72 percent wheat kernel milled from Michigan soft winter wheat 10. 97 1 10. 92 .50 77. 15 145 70 percent of wheat kernel, milled .46 3.799 166 from a mixture of Girka and Minnesota wheats 15. 02 2 11. 57 .81 72. 19 146 1st patent, milled from hard spring .41 146 wheat, Scotch Fife 10. 55 1 11. 08 1.15 76.85 .37 4.032 164 147 2d patent 10^49 1 11. 14 1.20 148 Patent, milled from hard spring 76.75 .42 4.006 164 wheat, Scotch Fife 12. 36 *12. 44 1.62 73. 07 .51 170 1 N X 5.7. 2 N X 6.25. 16 Available carbohydrate 63.60 percent; undetermined » N X 5.83. matter (pentosans, etc.) 9.02 percent. " Available carbohydrate 55.20 percent; undetermined *Vi^^"^^ ^^: 11^ and 140 were prepared from this sample. matter (pentosans, etc.) 9.78 percent. '^JN-conversion factor not reported.

102 TABLE 24.—Composition and heat of combustion oj jood items used in experiments on human diaestibility {table ^5)—Continued

Carbohydrate Heat of Test food, description Water Protein Fat combus- Ref. No. Total (by tion per diflerence) Fiber gram

GRAINS, GRAIN PRODUCTS—Con. Wheat, Wheat Products—Con. Flours, lower extractions—Con. 149 Patent, baker's grade, milled from Percent Percent Percent Percent Percent Percent Calories Scotch Fife 8. 01 *15. 50 2.22 73. 52 .75 170 151 Patent 11.07 *12. 75 .90 74. 84 14 . 44 97 163 30 percent of wheat kernel, milled from a mixture of Odessa, Cali- fornia and English wheats 14. 63 2 8.91 .96 75. 18 .32 146 Flours, other: 164 Semolina, milled from durum wheat, Kubanka 10. 77 2 11. 64 1. 27 75. 56 . 76 168 (Whole grain before processing) i7_. 8.76 2 12. 37 2.07 74. 92 1.88 165 Semolina, ^^ milled from durum wheat, Kubanka 7. 57 2 11. 57 0. 89 79. 06 0. 91 4. le 168 (Whole grain before processing) io_ 10. 48 2 12. 45 2. 48 72. 92 2. 83 1. 67 Flour mixtures: 173 "Bran flour," a mixture of 86 per- cent straight grade and 14 percent very finel}'- ground bran from hard Weissenburg wheat 9. 69 13. 96 1.48 73.62 1. 25 3. 876 168 174 "Germ flour," a mixture of 93 per- cent straight grade flour and 7 percent ñnely ground germ milled from hard winter Weissenburg wheat 9. 63 1 14. 87 1. 66 72. 97 . 87 3.962 168 Wheat breakfast foods: Whole grain and partially reñned: 175 Flaked 2. 72 2 11. 69 1. 49 79. 13 1. 88 4. 97 129 179 Meal 7. 06 2 11. 25 1. 89 78. 45 20 2. 10 1. 35 129 180 Meal 8. 08 2 16. 32 1. 47 72. 68 20 2. 07 1. 45 129 182 Meal 8. 08 2 15. 16 1. 35 74. 08 1. 33 126 184 Puffed, whole grain 4.90 2 15. 06 1. 94 76. 70 2. 34 1.40 129 185 Rolled 9. 19 1 9. 81 2. 27 77. 22 1. 07 1. 51 62 187 Rolled 11. 35 2 11. 14 2. 12 73. 85 1. 54 4.020 168 189 Shredded 6. 20 1 10. 60 1. 37 80. 06 1. 77 127 and 155 190 Shredded 5. 62 1 9. 97 1. 35 81. 27 2. 42 1.79 129 Reñned: 192 Endosperm, granulated 9. 35 Í 10. 54 . 85 78. 76 . 27 . 50 129 193 Endosperm, granulated 12. 68 2 11. 81 2. 40 72. 46 . 65 126 194 Endosperm, farina 10. 55 1 9. 70 1. 36 77. 97 , 44 . 42 62 195 Endosperm, farina 10. 58 1 9. 18 1. 10 78. 60 36 . 54 3. 877 62 196 Endosperm, farina 11. 37 *13. 03 . 77 74. 27 , 28 .56 97 Wheat breakfast food mixtures: 198 Wheat and barley malt 6. 47 1 11. 63 .77 78. 96 2. 17 4. 061 199 Wheat, whole grain and barley malt, ''Force" 10. 86 1. 65 74. 77 2. 86 3. 822 200 Wheat, whole grain and barley 62 malt mixture, "Force" 7. 37 1 9. 81 2. 13 78. 29 1. 85 2. 40 201 Wheat and barley malt, "Malta 9 Vita" 11. 32 1 12. 20 1. 52 72. 03 2. 93 3. 841 202 Branny portion, fraction of 73-95 30 percent 21 14. 7 *15. 7 4. 2 61. 1 7.6 4. 3 203 Branny portion, fraction of 82-95 30 percent 21 14. 3 *15. 0 4.4 61. 3 10. 3 5. 0

LEGUMES AND NUTS

Beans, dry (Phaseolus vulgaris) : 184 11. 21 2 18. 1. 63 64.89 4. 02 3. 885 210 Common white, navy beans. 3. 922 184 211 Common white, navy beans. 11. 19 2 20. 1. 58 62. 54 4.00 1 N X 5.7. 10 Items No. 165 and 187 were prepared from this sample. 2 N X 6.25. 20 Estimated by authors of article. u^^^r.^ " Item No. 164 was prepared from this sample. 21 The wheat was milled to 73 percent and the branny ^8 Composition for macaroni, dry; used here for flour as fraction obtained from the remaining portion.^ Keters TíO Snyder found by previous analyses that flour and uncooked original grain with a 5 percent loss from cleanmg. macaroni made from it have practically same composition. *N-conversion factor not reported. 103 TABLE 24.—Composition and heat of combustion of food items used in experiments on human digestibility (table ^5)—Continued

Carbohydrate Heat of Test food, description Water Protein Fat Ash combus- Ref. No. Total (by tion per difference) Fiber gram

LEGUMES AND NUTS—Continued Beans» dry—Continued 212 Common white, navy beans, skins Percent Percent Percent Percent Percent Percent Calories removed 13. 32 *23. 75 1. 71 59. 50 213 Common white, navy beans 12. 82 *22. 06 3.38 216 Kidney beans n. 25 2 25. 38 1. 41 58. 38 3.58 Cowpeas, dry (Vigna sinensis) : 221 Clay 13. 37 2 23. 19 1.45 58. 49 3.50 3. 915 222 Clay 10. 77 2 21. 94 1. 78 61. 79 3.72 3. 913 223 Lady 11. 32 2 25. 50 1. 73 57. 88 3. 57 023 224 Lady 10. 27 2 22. 38 1.75 62. 15 3.45 922 225 Lady 10. 05 2 23. 75 1.75 60. 94 3, 51 997 226 Whippoorwill 8.08 2 23. 00 1. 35 63. 64 3.93 071 227 Whippoorwill 12. 84 2 19. 94 1. 48 62. 17 3. 57 908 228 Whippoorwill 8. 36 2 21. 44 1. 70 64. 74 3.76 4. 040 Peas, dry (Pisum sativum) : 235 Peas 13. 0 2 2L 2 1. 2 6L 9 2. 7 236 Peas 13. 2 2 2L 2 1. 2 61.8 2.6 237 Peas 11. 53 2 22. 81 1. 51 61. 71 2. 44 238 Peas, split 12. 61 2 23. 44 . 71 61. 68 1. 56 Soybeans, Soybean Products (Glycine max) : 248 Soybean flour, about 6.5 percent fat. 4. 17 2 49. 31 6. 50 34.22 5. 10 5. 80 3. 716 249 Soybean flour, about 3.3 percent fat. 6.5 244. 1 3.3 40. 4 5.9 5. 7 3.480 252 Soybean curd (Tofu) 87. 80 2 5. 83 4 41 1. 25 . 11 .71 Ground nuts or peanuts (Arachis hyvooaea) : 259 Peanuts :._.._. 4.88 2 32. 64 47.33 12. 59 1. 98 2. 56 3. 040 261 Peanut flour, partially defatted 4 44 *58. 98 9. 69 23. 05 2. 54 3.84 Tree nuts: 264 Almonds (Prunus amygdalus) 4 42 2 17. 28 54. 30 21. 22 2. 58 3. 129 265 2. 78 Brazil nuts (Bertholletia excelsa) 4 33 2 19. 78 63.31 8.96 2.96 3. 62 3. 125 266 Brazil nuts 5. 28 2 18. 00 66.07 8.00 4. 22 2.65 3.397 267 Chestnuts, fresh (Castanea sativa).. 2 5.4 1. 4 38.3 268 Chestnut flour (Castanea dentata) _ . 6.36 2 6.38 3. 32 81. 54 2. 40 3.958 (Kernel before processing) 22 44. 89 2 3.85 2. 10 47.75 1.41 2.372 269 Coconuts (Cocos nucífera) 19. 17 2 5.25 51. 00 23.44 13. 77 270 1. 14 2. 712 Pecans (Carya illinoensis) 4 30 2 15. 67 71. 52 6.96 3. 17 3.551 271 Walnuts (Juglans regia) (presum- 1.55 ably Persian or English) 3.97 2 24 58 62. 92 6. 62 1.87 1.91 3.318 VEGETABLES

272 Beans, snap (Phaseolus vulgaris) _ _ _ 92. 44 2 1 16 . 13 5.44 274 Beets (Beta vulgaris) 82. 6 .83 *1. 9 . 3 13. 8 1. 4 .673 275 Beets 85, 4 *2. 2 . 2 10.8 276 Cabbage (Brassica olerácea var. 1.4 .599 çapitata) __ 94 7 *. 9 .3 3.3 1. 1 .8 .214 277 Cabbage """ 94 g *1. 0 .3 3.0 278 Cabbage ~~~ 94.4 . 9 . 210 * 9 . 1 3.7 . 9 . 203 280 Cabbage, savoy "'__ 89! 4 22! 1 . 6 6.6 281 ,Carrots (Daucus carota) "_ 90 53 1.3 2.86 .33 7. 40 1. 12 .88 282 Carrots ~ 86." 3 2 1. 6 .2 11.0 283 Collards (Brassica olerácea var. .9 acephala) 88. 44 2 3. 13 . 54 5.53 L51 2.36 284 Corn, green (Zea maî/s) ~_" 76^0 *4. 9 1. 4 17. 3 286 Potatoes, white (Solanum tubero- .5 .4 1. 112 sum) _ 79 5 *2. 2 . 1 17.4 . 4 .8 .848 287 Potatoes, white '__'_ 78.3 *2. 3 . 1 288 Potatoes, white ~ ¿l! 2 18.4 .9 . 900 *1. 9 .3 15.5 1. 1 .782 291 Potatoes, white "_~ 73*4 *2. 3 292 Potatoes, white ~ 74.33 23.3 1.0 *2. 38 .03 22. 32 ,28 .94 293 Potatoes, white ~ 80 16 2 1.49 294 Potatoes, white 23 " 75^ j .07 17.35 39 .93 2 2.0 21. 8 295 Potatoes, white 77.66 2 2. 04 1.0 1.014 296 Potatoes, white 74. 80 19.47 . 84 2 1.20 23. 19 .81 2 N X 6.25. 22 Item No. 268 was prepared from this sample. ^^Z^i^^''^§^ ^^ ^^''•'■^^ samples weighted by their con- sumption during period of digestion experiment. '*^N-conversion factor not reported.

104 TABLE 24.—Composition and heat of combustion of food items used in experiments on human digestibility (table ;g5)—Continued

Carbohydrate Heat of Test food, description Water Protein Fat Ash combus- Ref. No. Total (by tion per difference) Fiber gram

VEGETABLES—Continued Percent Percent Percent Percent Percent Percent Calories 297 Potatoes, white 73.66 2 1.95 23.38 1.01 69 298 Potatoes, white 76.23 2 2. 11 20.70 .96 69 299 Potatoes, white 77.66 2 2. 04 19.47 .84 69 300 Potatoes, white 74. 80 2 1.20 23. 19 .81 69 301 Potatoes, white 23 74.3 2 1.8 23. .8 69 302 Potatoes, white 23 79.4 2 1. 4 18. .9 69 311 Pumpkin (Cucúrbita pepo) 84.01 2 1. 94 . 19 13.23 1.30 . 63 134 312 Sweetpotatoes, partially dried {Ipomoea batatas) 4.96 2 1.71 .76 90.27 7.65 2.30 134 FRUITS 322 Bananas {Musa paradisiaca var. sapientum) 77. 15 2 1.60 .24 20.20 .52 .81 75 323 Grapes {Vitis spp.),"^^ mixture of Tokay, Muscat and Cornichon.. 86.8 2.7 .2 12.0 .5 .3 75 MISCELLANEOUS 330 Yeast, dried 6.82 25 47. 25 4.478 87 331 Yeast, fresh compressed 69. 92 2 15. 20 1.443 87

2 N X 6.25. 24 Weighted average of 3 kinds of European type grapes 23 Average of several samples weighted by their con- used in the digestion experiment. sumption during period of digestion experiment. 26 N X 6.25. Authors also reported 7.05 percent protein N and 0.51 percent purine N.

105

U. S. GOVERNMENT PRINTING OFFICE: 1955