■^Ä*^^^/, CORE LIST r ENERGY VALUE OF FOODS • • • basis and derivation UNITED STATES DEPARTMENT OF AGRICULTURE Agriculture Handbook No. 74 mmmgiimgimmi ENERGY VALUE OF FOODS •I. ■ basis and derivation Do«miem Delivery SeM«sB,anch 'NíAL Sid Ï'' ' "-'• '■- .c.,r^,, . Bernice K. Waff , ' *""ô, A10 2Ü7Ü5■^^'"cJoS f Human Nutrition Research Branch AGRICULTURAL RESEARCH SERVICE UNITED STATES DEPARTMENT OF AGRICULTURE Agriculture Handbook No. 74 Slishtly revised February 1973 For sole by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 Price $1.25 domestic postpaid or $1.00 GPO Bookstore Stock Number 0100-02770 PREFACE The kilocalorie, which has been defined as the amount of heat energy needed to raise the temperature >f a kilogram of water 1° C, is the unit that has been used traditionally for expressing the energy value >f foods. Recently the International Bureau of Weights and Measures has recommended that the joule, L unit of energy applicable to electrical, work, and chemical energy, be adopted as the preferred unit for L11 forms of energy. The joule is derived from basic units in the International System of Units (SI) and s defined as a measure of force (newtons) times distance (metres). In the interest of uniform nomenclature, some nutritionists have proposed that the kilojoule replace he kilocalorie. The conversion factor for expressing kcalories as kjoules, as recommended by the Com- nittee on Nomenclature of the International Union of Nutritional Sciences, is 1 kcalorie equals 4.184 goules, based on the kcalorie determined at 14.5° to 15.5° C. Use of kjoules in place of kcalories as the unit of measure for energy in no way invalidates the )rinciples underlying the Atwater system for determining energy value of foods and the energy needs md energy expenditures of man. The Atwater system is based on the demonstrated principle that the oxygen used, the carbon dioxide ormed, and the energy evolved in oxidizing foods are the same whether this oxidation takes place in the )ody of man or in a bomb calorimeter. Furthermore, Atwater has clearly shown that by applying appro- )riate factors, which allow for metabolic losses, to the contents of protein, fat, and carbohydrate in a ood, the physiologically available energy value of that food can be calculated with outstanding accuracy. The results obtained by this procedure are in excellent agreement with data from measurements made >y bomb calorimetry on food and metabolic products. Results of studies by Atw^ater and others could )e expressed either in kcalories or in kjoules. 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 5 Comparison of calculated and determined avail- Other sources of energy 6 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 Definition of terms 8 supplies 48 Digestibility of fat, carbohydrate, and protein. __ 8 Conclusions 51 Availability of energy from digested nutrients Literature cited 51 9 Appendix. Tabular summary of experiments on Fat 9 digestibility 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 2 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 materials 3 14. Energy values of wheat ñours calculated by use of specific energy factors for protein, fat, and 3. Factors for calculating protein from nitrogen 28 content of food 4 carbohydrate 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 5 16. Coefficients of apparent digestibility for grain 5. Comparison of calculated heats of combustion products 32 with results of direct determinations 6 17. Comparison of determined and calculated gross 6. Fresh fruits classified as to organic acid content. 7 38 7. Factors for heats of combustion and fuel values energy values of potatoes 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 digesti billty 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 food groups as used in present-day mixed which Atwater originally obtained the calorie- 49 nitrogen ratio of 7.9 for urine 17 diets 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 coeflfi- 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 98 foods of plant origin for human subjects. _ 60 24. Composition and heat of combustion of food GrainSj'grain products 60 items used in experiments on human digest- Legumes and nuts 87 ibility (table 23) 100 IV Energy value of foods . basis and derivation INTRODUCTION Accurate evaluation of the energy value of foods tions and misuse when applied to individual foods is essential for dealing with problems of normal and different types of diets (114y ^^p)-^. nutrition, undernutrition, or obesity. The classic The Food and Agricultiu-e Organization, faced investigations of Professor W. O. 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 (55) 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 during 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 Ma3mard, 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, thé United Kingdom, and in Agriculture Handbooks No. 8 (185) and No. 34 this country. 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 oxidizedjin and carbohydrates contain carbon and hydrogen the calorimeter.