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Fats and Fatty Acids

Fats and Fatty Acids

and Fatty

GALLIE MAE COONS

FATS often have been prized of processed , from roasted nuts articles of diet in man's struggle to main dishes. for . From early times they Our total and proportional con- have denoted prosperity and hospi- sumption of fats and has climbed tality, as when the fatted calf was to an alltime peak, and the kind and prepared for merrymaking and the amount of fats we eat have come under widow shared her with the prophet. the scrutiny of economists and scientists. Scientific and economic concern makes our meals palatable and about dietary fats goes in cycles. satisfying. It is the most concentrated Sometimes the cycle is geared to dietary source of energy—9 Calories war and famine, when fats tend to be a gram, compared to 4 Calories in scarce and are among the first foods carbohydrate and protein. It promotes to be conserved and rationed. When efficiency in the utilization of protein food surpluses mount, fats float to the and carbohydrate. It facilitates the top and are among the first to be utilization of fat-soluble vitamins. used extravagantly. Some fats and oils are important Pioneers in every civilization have sources of vitamins A, D, E, and K. been ingenious in ways of conserving Fats provide various amounts of and using fats and in bartering them fatty acids known to be essential in in international trade. Still today diets and many other fatty acids, many peoples have a low consumption which may have nutritional functions of fats and oils. that we do not know now. Our food technology in the United The amounts of fat, visible and in- States has made possible improved visible, in food supplies in the United supplies of separated fats and oils States at retail level have been esti- from , grains, cottonseed, soy- mated at 32 percent of the Calories in beans, , olives, and . 1910, 35 percent in. 1930, and 40 per- Agricultural research has led to cent in 1950. They have continued to higher acreage yields of the oilseeds rise more steeply during the 1950's. and grains and animals of high The amounts used in households are fatness. The flavors of cooked fats much the same—about 30 to 33 per- have been imparted to many kinds cent of the Calories before 1900, 35 to 74 FATS AND FATTT ACIDS 75 38 in the mid-1930's, and 42 to 44 in after 1900. Their diets contained, re- the mid-1950's. spectively, 26 and 30 percent of the Farm famihes tend to use more fat Calories from fat, 8 and 9 percent from than city famiHcs do, and northern protein, and 66 and 61 percent from families more than southern famihes. carbohydrate. As the proportion of Calories from People in densely populated coun- protein has remained about the same— tries are said to subsist on such food an average of 11 to 12 percent at the patterns, often with even less than 30 household level—the shift to larger percent from fats at any time. People proportions of Calories from fat has in some countries who have fat intakes been at the expense of carbohydrate. that are one-third to one-half that in Thus, in the North Central States, the United States get less than 20 per- farm families in 1955 had 44 to 46 per- cent of the dietary fat from all animal cent of their Calories from fat and sources, as much as 40 percent from about the same proportion from carbo- cereal grains, and 25 percent from hydrate; 40 years earlier, Calories from peanuts and other oilseeds. fat ran 33 to 35 percent and from car- bohydrate 53 to 55 percent. THE SOURCES of fats consumed in the Families with high incomes tend to United States follow changing food have even more Calories from fat patterns. The proportions of Calories than from carbohydrate. Low-income from dairy and meat products and groups select more Calories from car- from separated fats and oils have in- bohydrate. creased steadily since 1900. The few reports of individual food The average household diet in 1955 intake—the amounts people actually had about 25 percent of its fats from ingest—by adults since 1900 indicate dairy products; 24 percent from 38 to 42 percent of Calories from fat, products; 14 percent from , veal, 45 to 55 percent from carbohydrates, and lamb ; 13 percent from and 13 to 15 percent from protein. and ; 6 percent from oils The proportions are about the same and salad dressings; 6 percent from for women as for men and for the few poultry, , and eggs; and 12 percent groups of elderly people on whom re- from baked goods, nuts, fruit, and ports were made. vegetables. These scattered figures on individual Of the 25 percent from dairy prod- intake do not confirm the time trends ucts, more than half was from noted for household diets and retail and ; 7 percent was from but- food supplies, but they confirm the ter, separated from the other milk tendency to a high level of intake of fat ; and the rest was from cream in the United States. and ice cream. Figures from chemically analyzed We should bear in mind that natural diets and school lunches support the unseparatecl fats are associated with conclusion that the average diet carries the protein, minerals, and vitamins more than 40 percent of its Calories characteristic of the food, as in milk or from fat and that diets of some individ- pork, and also carry some vitamins, uals carry 50 percent or more. such as A, D, and E, which are useful The fat may drop to 30 percent or in the of fats. even 20 percent of the Calories in times of war or economic stress. How SHALL we choose fats to eat Often 25 to 30 percent is recom- when we have much and many kinds mended as desirable for any population of them in the store and on the table? at any time. The lowest averages re- Some who want to control v/eight ported from any study in the United may be interested in whether the fat States, however, was for two groups of is visible (as in , , families in the southern mountains just salad oils, and other separated fats or 76 YEARBOOK OF AGRICULTURE 1959 in the visible fat on meat). The fat on Much variety in fats comes from the meat can be trimmed away, but that kinds of fatty acids linked to the glyc- means waste. The less readily appar- erol—whether all three are alike or ent fats, those mingled, blended, or all are different, whether all are satu- absorbed into food products, make rated (contain all the hydrogen they good eating, but they cannot be can carry) or of various degrees of un- trimmed away by the consumer. saturation, and whether they are mostly Some fats are solid—more or less short-chain (under 12 ), long- firm—at room . Others chain (12 to 18 carbons), or extra long- are plastic. Many come naturally as chain (20 carbons or more) fatty acids. oils. These characteristics are impor- Fatty acids that have 18 carbons in a tant for baking, , and mak- chain make up about 80 percent and ing salad dressings. those with 16 carbons comprise about Almost any fat can be used for any 10 to 15 percent of the fatty acids in culinary purposes by suitable adapta- average diets. tions in cooking procedures, however. Short-chain fatty acids occur mostly The of a fat can be al- in milk fat and in . Extra tered in many ways by the technolo- long chains occur in fish oils. gist, but consistency does not always Fatty acids that are common in food denote properties important in diet. fats and oils fall into three broad classes according to their degree of saturation. ONE WILL do well to understand the The fully saturated fatty acids make composition and structure of fats and up about 40 to 45 percent of those in fatty acids in order to know their com- average diets in this country. They are plicated role in nutrition. The details rather stable chemically and account are technical, however, and some read- for much of the firmness of fats at room ers may wish to skip this section. . A pure fat is composed of molecules Saturated fatty acids may be of any of (a trihydroxy alcohol, the chain length, from 4 to 18 or more same as glycerin), to each of which i, carbons. The most common ones and 2, or 3 fatty acids are linked to form their chain lengths are: Stearic (18), , , or tri- palmitic (16), myristic (14), and glycérides, respectively. lauric (12). Fatty acids are hydrocarbons con- Beef fat contains 20 percent of stearic sisting of a chain series of carbons, each and about 12 percent. Other of which is able to carry 2 hydrogens, animal fats run higher. Most animal but with 3 hydrogens () fats and contain about at one end, and an acid (carlDoxyl) 25 to 30 percent of . Palm group at the other end, which con- oil has about 40 percent. nects to the glycerol. The monounsaturated fatty acids Natural fats, as in meats, grains, and (monoenoic) are those with one reac- nuts, are made up mostly of triglycér- tive unsaturated (^'doublebond") link- ides with only trace amounts of the age, which has 2 hydrogens missing. mono- and di- forms and some free The best example and the one most fatty acids. Processed fats, such as abundant in foods is contain- bydrogenated commercially hardened ing 18 carbons, which alone furnishes shortenings, may contain up to 20 per- about 40 percent of all the fatty acids cent of monoglycerides and diglyc- in the average diet in this country. It erides. represents 70 to 75 percent of the fatty It makes some difference nutrition- acids in and the bydrogenated ally which is attached in the (commercially hardened) shortenings; middle position on the glycerol mole- 50 percent or more of the fatty acids in cule and whether an outer position is lard and oil; and 40 percent in open or is linked to another substance. beef, lamb, and poultry fat. Its nutri- FATS AND FATTT ACIDS 77 Structure of Mixed Triglycéride—A Monosaturated Fat

H HLHHHHHHHHHHHHHH Í I I I I I I I I i I i i I I H—C—(ÖH i HjO—C ::—c—c—c—c—c—c—c- c- c c- -c-c-c I c H I _i i 1 :i 1 i I i ¡ ) i (Saturated) HHHHHHHHHHHHH|H I I o H H H H H H H H H H H I i I I i I i Í ■îl ! Okie Acid H—c—fonTHJ« ;—C—C--C• -C--C- -C—c-=c-c-c-" C - C - C- c: C—H (:i8-2H I J. i ! il I J. _l (Monounsaturated) H H H H H H H H H H H H H Hlíi H I I HHHH H HHH Hl K Ml; I ; I I I I I n—C- |OH I HjO—c- C—c -c- c- C-—G C- C--C-C-C—C C-H Qs- 4H .1 I I I i lililí '^\ (Polyunsaturated) H I H H H H H H H H H H H H H \ H I Glycerol iCarboxyl Aliphatic (Hydrocarbon) Chain I Methyl molecule- j group I group

tional role in man has not been fully Most common moaounsaturated defined, however. fatty acids, including oleic, have the The polyunsaturated fatty acids, a reactive unsaturated linkage in the heterogeneous group, include some gth position—that is, between the gth essential fatty acids and the extra and loth carbons. Linoleic acid, with long-chain fatty acids (20 to 26 2 reactive linkages, has them in the carbons) common in fish oils. The gth and 12th positions. The descriptive degree of unsaturation may involve chemical name is g, 12-octadecadienoic. 2, 3, 4, or more linkages in the chain, , with 4 reactive with correspondingly 4, 6, 8, or more linkages, has this chemical name: hydrogens missing. Polyunsaturated 5,8,11,14-eicosatetraenoic. fatty acids are sometimes classed as The polyunsaturated fatty acids dienoic, trienoic, and tetraenoic, and considered essential for nutrition are so on, depending on the number of linoleic, linolenic, and arachidonic. linkages affected. Because arachidonic acid can be The position of unsaturadon along formed from linoleic acid in the body, the chain is important chemically and it is not really a dietary essential. nutritionally as well as technologically Besides, it constitutes less than i in processing. percent of animal fats (except in Nutritionally, the position of unsat- and some pig fats, which contain uration may determine the point of more than 2 percent) and less than breakup of the chain in metabolism I percent or none of vegetable fats. and how well the body can handle Therefore it may be disregarded in the remaining fragments. choosing dietary fats. The positions of carbons in fatty has a dififerent and acids are numbered successively, be- perhaps less important nutritional ginning at the carboxyl (acid) end role than linoleic and occurs only in of the chain, which attaches to the small amounts in food fats. Soybean glycerol. The position of linkage oil, with 7 percent, is the highest. carries the number of the lower or first Of the three, linoleic becomes the of the 2 carbons that it joins. center of dietary importance. It is 78 YEARBOOK OF AGRICULTURE 1959 relatively more abundant in foods than substances that are not true fats but the other two and must come from diet may be nutritionally important. because it cannot be formed by the There are processed fats and natural human body. fats and many kinds in each class, so Sources of linoleic acid include many that this distinction is not a good basis grain oils and seed oils, which contain for selection by consumers. 50 percent or more. Fats from nuts, pea- Hydrogénation, one type of process- nuts, and poultry carry 20 to 30 per- ing, induces hydrogen to enter points cent. Outstanding exceptions are fat of unsaturation in the fatty acid chains from , which has more than 60 to increase the saturation of the fat percent of linoleic acid, and fat from and achieve varying degrees of firm- , which has about 2 percent. ness sought for specific uses. It also Fats from such fruits as prevents oxidative rancidity and thus and olive contain about 10 percent of greatly prolongs the storage life of the linoleic acid. Those from leafy vege- fat. Only about 15 percent of the die- tables and legumes run higher, 30 tary fat that reaches the consumer has percent or more, but the total amount been exposed to hydrogénation. of fat in greens is low. When hydrogénation w^as first used, Doubdess the diet should provide only a fraction of the fat was exposed some linoleic acid every day unless to the process and then blended with the body (as in weight reduction) the untreated oil to a desired consist- is mobilizing tissue fat known to ency. contain this fatty acid. A later practice is to expose an Linoleic acid is necessary for growth entire lot in a continuous controlled and reproduction and helps protect process, so that more fatty acids are the animal against excessive loss of altered but to lesser degrees of satura- water and damage from radiation. It tion. This process tends to cover up is essential for normal skin conditions most of the essential linoleic acid and in babies, who require about 5 percent convert it to the already abundant of the Calories from this source. olcic acid. When it is fed as 25 percent or more The technologist refers to non- of the fat, linoleic acid lowers selective hydrogénation, by which in adults under certain saturation of monounsaturated and dietary conditions. It appears to have polyunsaturated fatty acids proceed other metabolic functions that have simultaneously, and to selective hydro- not yet been defined fully. (Cholesterol génation, by which polyunsaturated is .a complex, fatlike material that fatty acids are converted largely to occurs in all animal tissues, notably monounsaturated before much of nerve tissue, bile, gallstones, egg , either is converted to saturated. Selec- liver, spleen, tissue.) tive hydrogénation thus changes most Some animal fats and vegetable fats of the essential linoleic acid to oleic or oils are fairly similar chemically. acid, which is already abundant. Both and coconut oil, for By changing the conditions of hydro- example, contain high proportions of génation, the technologist can get short-chain fatty acids. Beef fat and various physical and chemical char- coconut oil contain less than 2 percent acteristics in the finished product. of linoleic, one of the fatty acids that Many of the characteristics can be are essential in the diet. obtained also by blending proper contains more than 6 times as much assortments of natural fats and oils. linoleic as olive oil, and The chemist has not yet found out up to 10 times as much as the fat of all that happens to a fat or oil during animals. processing. Biochemists and physiolo- Both animal and vegetable fats con- gists cannot yet tell us how the body tain up to 5 percent of various fatty utilizes some of the products formed FATS AND FATTT ACIDS 79 during hydrogénation, such as isoacids, on the glycerol molecule are split off transisomcrs, and conjugated fatty first. Those in the middle position are acids. split off less rapidly, if at all. At least one study has shown these The rate of and absorption ''unnatural" products to be ineffective depends also on chain length and on as essential fatty acids. Another study the amount and position of the satu- indicated that conjugated forms favor rated fatty acids, if any, on the glyc- high blood cholesterol. erol. Obviously it is not enough to The rate depends at first on the de- distinguish saturated and unsaturated gree of emulsifixation (separation into "fats" for nutrition purposes, because fine droplets) of the fat, which is none there are varying degrees of saturation in separated fats or oils and partial in in all fats. All oils contain some others, as in ç^^g yolk, milk fat, and saturated fatty acids. All solid fats mayonnaise. Emulsification in the in- contain some unsaturated fatty acids testinal tract is greatly aided by the even though fats that are firm at room bile. temperatures consist mostly of satu- Persons with defective or limited se- rated fatty acids. cretions of bile have less efiiicient di- Fats that are soft or liquid at room gestion of fats than normal persons. temperature may be called unsatu- Early experiments showed digestibil- rated but may contain different assort- ity by normal young adults to be 90 ments of fatty acids. Olive oil, for percent or more for various fats, but we example, is liquid because it contains need new studies with fats fed in cus- 75 percent or more of oleic acid (one tomary mixed diets and a better un- linkage unsaturated); oil derstanding of the of fats contains nearly 75 percent linoleic and the physiology of absorption and acid (two linkages unsaturated); lin- transport. may contain up to 65 percent The various products of fat diges- of linolenic acid (with three linkages tion—some diglycerides and mono- unsaturated). , but mostly free fatty acids value, based on a laboratory and glycerol—are absorbed from the test showing uptake of iodine by all intestine along with , choles- unsaturated points in the fatty acid terol, and other , which also are chains, is a gross measure of total linked with some fatty acids. unsaturation or potential hydrogen Some fatty acids may be recom- uptake, but it does not indicate the bined into glycerides, and some posi- particular fatty acids present. tions may be interchanged for others runs below 10 in a in passing across the intestinal wall near- like coconut oil, into blood and systems. The more than 100 in most vegetable oils, short-chain fatty acids appear less and up to 200 in a highly unsaturated likely to be reformed and may go more oil, such as and some fish directly through the blood to the liver. oils. They may present more problems in The use of radioactive elements metabolism than the common long- makes it possible to follow fatty acids, chain ones. cholesterol, and other lipids (fatlike After absorption, about half of the substances) through digestion and ab- fatty acids in circulation appear linked sorption to their destinations in the with cholesterol and , body organism. the remainder as glycerides or free. In the digestive tract, fat-splitting The proportions in such combi- in the gastric, pancreatic, nations are indicators of normalcy and intestinal juices take their turn in in metabolism and of the effects separating some of the fatty acids from of various food fats and diets. Values glyccrol. Those in the outer position regarded normal in the plasma of per- 8o YEARBOOK OF AGRICULTURE 1959 sons after fasting overnight are 45 per- from other causes, including liver in- cent of the fatty acids in glycerides, jury. 35 percent in phospholipids (mostly The lipid levels return to normal lecithin), and 15 percent in cholesterol. more readily in persons accustomed to The rest are free or in loose protein physical activity than in persons sed- combinations. entary or inactive for hours before and In plasma of blood and lymph, the after meals. Lipids arising within the products of fat absorption, some of body, such as during conversion of ex- which have been through the liver, cessive nonfat Calories to fat, may are transported to tissues along with augment the burden of disposal. other lip ids from internal body sources. Sustained elevated plasma lipid levels The lipids travel as parts of complex are considered undesirable. The under- particles of various sizes called lipo- lying cause may be that the body has proteins, in "wraps" of protein, which lost some hormone or capacity keep the fatty substances miscible with to convert, oxidize, or dispose of ex- the watery plasma during transport. cesses, or that the is The largest of these particles, called being flooded continually with lipids , may cause the plasma to from the foods eaten as well as from appear milky after fat-rich meals. Other internal , but in any case particles, graded into successively small- the longtime consequences may be er sizes down to ultramicroscopic, are serious. known as - (the heavier) and Fatty acids that are used for muscu- beta- (the lighter) , and lar energy may be oxidized in any tis- probably are elaborated in the liver. sue of the body. The level of beta-lipoproteins is often The first step in oxidation is breaking elevated in abnormal fat metabolism off from the fatty acid chain, a two- and can be raised experimentally by fragment known as an active feeding some fatty acids. Ratios of . Failure in oxidation may arise alpha- to beta-lipoprotcins below 0.5 from inability to break off the are found in myocardial infarction (cor- because of the unnatural structure of onary damage). Ratios around the fatty acid chain or because of phys- 0.7 or more occur in persons considered iologic defects of the body. The failure well. is due more commonly to lessened Levels of lipoproteins normally are ability of the body to proceed with elevated after meals and are cleared completion of the oxidation of the ace- out of the plasma in 3 to 6 hours. The tate to and water as a various lipids are delivered where they result of deficiency of some hormone, are needed to the skin, brain, and nerve enzyme, or vitamin. tissues or to fat depots or are oxidized If the kind of fat being laid down in by the tissues to produce energy for adult human tissues comes mainly heat or activity. from absorbed fatty acids, it will re- During high lipid levels, the blood semble the fat from the food eaten, tends to clot more easily, regardless of especially the long-chain saturated and the kind of fat ingested, but clotting unsaturated fatty acids. also depends on the age of the person, If the fat is synthesized internally the blood enzyme levels, and other met- from excess total Calories, such as from abolic states. sugars and proteins, saturated fatty High lipid levels after meals return acids will predominate in the fat de- to normal more slowly—in 12 hours or posits, and none will be linoleic, longer—in extremely obese persons, in because the body cannot synthesize it. elderly persons with atherosclerosis (a In this respect man metabolizes fat as condition accompanied by thickened do pigs, w^hich lay down a firmer, more walls in of the heart), and in saturated fat on a corn ration high in persons with high blood lipid levels carbohydrate, from which fat must be FATS AND FATTY ACIDS 8i synthesized, than on a peanut-con- present in atheroma (plaque forma- taining ration, from which a preformed tions on arterial walls). oil containing as much as 20-25 per- Modern analytical methods have cent hnoleic acid is absorbed. shown that the total free and combined Ruminant animals, like cows, absorb cholesterol in atheroma is no higher short-chain fatty acids, which have than the total in normal circulating been synthesized by micro-organisms , but that the free cho- in the . Short-chain fatty acids lesterol is about five times as high as thus predominate in the fat of cow's that in normal blood. Oleic acid also milk. The shortest is , with has been shown to be twice as high in a chain length of only 4 carbons. More atheroma as in normal plasma. than 30 kinds of fatty acids occur in Many investigators have reached a butterfat. conclusion that atherosclerosis, with The fat in human milk contains 2 to its generalized thickening of the inner 4 times as much linoleic acid as the arterial wall, might be a consequence fat of cow's milk, but we do not know of abnormal cholesterol metabolism, whether this is merely a reflection of whatever the metabolic failure. diet or is due to liver function or to This view has been supported also some special activity of the mammary by studies with experimental ani- gland to meet particular needs of the mals—rabbits, chickens, mice, rats, offspring. guinea pigs, dogs, and monkeys—in Human body fat contains about 11 which elevated blood cholesterol pro- percent of linoleic acid, according to duced by diet, drugs, or other means German analyses made nearly 30 tended to result eventually in arterial years ago. This figure is only a little damages resembling in many respects higher than the 10 percent estimated those found in human atherosclerosis. content of the average diet in the Thus attention has continued to be United States in 1955. centered on blood cholesterol. In the depression of the 1930's, a THE IMPORTANCE of blood cholesterol paucity of atheroma was noted in the in the metabolism of fat and what poorly nourished bodies on which regulates its formation and distribution autopsies were performed. As early as in the body has been an area of inten- 1904, an increase of 40 percent was ob- sive research, which so far has given us served in diseases of the circulatory ap- only partial answers. paratus and kidneys and a 15-percent Common indicators of abnormal fat increase in cancer in one generation. metabolism include plasma cholesterol Attention was directed in 1940 to levels, cholesterol- ratio in the fact that heart disease was then a plasma, serum patterns, worldwide problem. The war period, and the distribution of fatty acids however, imposed food restrictions on among the lipid fractions—, peoples throughout the world and cholesterol, and phospholipid—in the slackened the mortality rates from dia- blood. Measurement of the plasma betes and other metabolic disorders as cholesterol is the oldest and simplest well as from cardiovascular diseases. method of testing, and the results are The trends reversed after the war to most easily interpreted. accelerated rates, particularly from High cholesterol levels in plasma are coronary damage, and aroused world- among the complications in diabetes wide attention of scientists and clini- in consequence of abnormal metabo- cians, while cardiovascular diseases lism of fats (as well as sugars), although rose rapidly to top place as the re- the high levels are somewhat better ported cause of deaths in the United controlled since began to be States. used in the 1920's. More than 100 Revived interest in metabolism of years ago (1847) cholesterol was found cholesterol has continued as research 477248°—59— 7 82 YEARBOOK OF AGRICULTURE 1959 has associated atherosclerosis with high of or sex hormones. Choles- plasma cholesterol and more or less terol is converted by the liver into bile with an estimated high level of fat acids and secreted into the intestines, consumption. where part of the cholesterol is reused Other observers linked it with a high in the emulsification of fats and absorp- level of protein from foods of animal tion of fatty acids. This initiates origin. The availability of radioactive another metabolic round for the elements after the war made it possible cholesterol, which is shown by isotope to use labeled carbon to follow the measurements to require 2 to 3 days. course and fate of different parts of the Some cholesterol in various forms cholesterol molecule in metabolism may be disposed of through the bowel, and thus greatly refined the techniques eventually half or more, and such of research. disposal seems to be favored by diets Cholesterol is a normal and essential high in linoleic acid. Failure of con- constituent of blood, nerve tissue, and version to bile acids or of disposal other parts of the body of animals. through the bowel may result in Corresponding substances found in backlog accumulations that show up plants are known as plant sterols and in high blood cholesterol. Within include the sitosterols commonly found limits, however, the level of plasma in vegetable oils. They may be poorly cholesterol may be less important to absorbed by people, however. Some the system than is the kind of fatty may prevent the absorption of some acids carried, its relation to the fats. Others elevate blood cholesterol. phospholipid level, or to the level of Cholesterol is normally synthesized loeta-lipoprotein, w^hich also transports in all cells of the body and especially cholesterol. in the liver from a substance called A cholesterol-phospholipid ratio squalene, which has been formed from (C/P) of 0.70 to 0.80 is characteristic in acetates (2-carbon fragments). Squa- persons with normal or low choles- lene fed to human beings causes a rise terol. Higher ratios, 0.90 to i.o and in blood cholesterol in an hour. It above, suggest abnormal fat metab- reaches a maximum in 7 to 21 hours. olism, whether due to high cholesterol Dietary fat is not essential for the or to low phospholipid in the plasma. formation of cholesterol, but some fatty acids favor its absorption, and HUMAN PLASMA cholesterol levels excessive lip id s in circulation may differ widely because of many condi- favor its formation. tions, the most common of which are Dietary cholesterol from food, about associated with advancing age. 0.5 gram daily in the average diet, Other conditions include the kinds usually is a minor source compared and amounts of fat and other constitu- with the amounts, 2 to 3 grams daily, ents in the diet, the planes of regular that the body is capable of forming. physical activity, the nature and extent Excessive intakes of cholesterol-rich of emotional stress, and periods of men- foods can push the amount up toward struation and menopause in women. 5 grams daily, but that is seldom the In the same individuals over periods case. Moreover, high dietary choles- of months, the level may fluctuate in a terol tends to suppress normal body wide range, 15 percent above and be- synthesis of cholesterol. low in normal persons and as much as Cholesterol normally transports 30 to 40 percent in persons with high about 15 percent of the fatty acids of cholesterol. the blood, mostly the unsa tura ted. It In children, cholesterol levels in the may influence some immunological plasma range from 150 to 250 milli- reactions in protecting the body from grams percent, with erratic trends in certain injurious substances. adolescence. Cholesterol is used in the production In this country, women before meno- FATS AND FATTY ACIDS 83 pause have levels of i8o to 200 milli- mental animals by higher dietary in- grams percent or even less. takes of magnesium, pyridoxine, and Men under 50 years of age have . Dietary levels of , levels around 200 to 220 milligrams. potassium, and calcium appear also After these ages, the average level in to be involved. men continues to rise gradually. The average level in women rises sharply THE LOW CHOLESTEROL levels char- and exceeds that of men after about 55 acteristic of some nationality groups years of age, when both are in the doubtless reflect a combination of range of 240 to 260 or even 300. factors—hereditary, hormonal, dietary, A lower average level has been noted occupational, or other environmental in persons older than 65 years, but that factors—although usually a diet low may mean persons with low levels are in fat is one factor. more likely to live beyond that age. For example, Yemenites are said to Men with histories of coronary artery have lived apart for some 2,000 years damage have been found to have much on diets of grain, vegetables, and higher plasma cholesterol levels, espe- vegetable oils, with less than 18 cially in ages 25 to 40 years, when percent of the Calories from fat. the levels were 50 to 100 milligrams Yemenite immigrant men arriving above the average for men apparently in Israel have been found to have normal. average cholesterol levels of 160 milli- Men living in a county home on a grams at ages 55 to 60 years. Those limited diet were found to have plasma who had lived in Palestine 20 years or cholesterol levels markedly below re- more, having diets containing more tired men of like ages who lived in their than 20 percent of the Calories from own homes on more liberal, freely fát, including some animal fats, aver- chosen diets. aged 200 milligrams. European Jewish Plasma.cholesterol is elevated in dia- immigrants, who had more liberal betes, during periods of gain in weight, diets, averaged more than 240 milli- low activity, and other condi- grams percent at similar ages. tions of depressed energy metabolism. The death rates from atherosclerosis It is elevated by several dietary factors, in the three groups were reported to including calories in excess of energy be around 5, 35, and 85 per 100,000, needs, high intakes of fat, particularly respectively. certain saturated fatty acids and dietary Similar observations have been made cholesterol; by high protein intakes, on the cholesterol levels of Japanese especially of animal proteins and those living in Japan with less than 15-20 high in the sulfur-containing amino percent of the Calories from fat; those acids (methionine and cystine and per- in Hawaii, with about 20 percent; and haps others) ; and by and rap- those in the United States, with more idly absorbed sugars. than 30 percent. High cholesterol in the plasma is Difí'erences in the amount and kind lowered by relatively high intakes of of dietary fat among these groups, linoleic and perhaps other polyunsatu- however, appear small compared to rated fatty acids, by high intakes of levels of 40-45 percent in diets in this nicotinic acid, by dietary starches in country and certainly were not the place of sugars, and by strict vegetar- only dietary differences in these situa- ian-type diets, as well as by stepped-up tions. The occupations, physical ac- energy metabolism such as from regular tivity, and emotional stresses also were exercise, thyroid hormone, and other different. For example, laboring Jap- agents that stimulate metabolism. anese who worked on the plantations Damage to arterial walls in the pres- had cholesterol levels well below the ence of high plasma cholesterol has average for this race in the same been lessened or averted in experi- location. Fatty Acids in Some Animal and Plant Products CO [Grams per i oo grams of total fatty acids]

Saturated fatty acids Unsaturatedfatty acids

Palmitic Stearic Oleic Linoleic Other un- Source of fat Total C 16 C18 C i8~2 H C 18-4 H saturated MILK: Buffalo 66 31 15 27 I 6 Cow 59 27 12 35 3 3 Goat 66 29 8 26 Human 48 23 7 36 8 8 Mare 41 16 3 19 8 32 MEATS: Pork: 33 22 10 50 10 7 40 27 12 48 6 6 Pork cuts 38 22 14 44 9 9 Pork liver 36 14 19 28 5 31 Rabbit 39 29 4 37 12 II Ruminant animals: Beef 50 29 20 46 2 2 ^ Deer 66 25 35 25 3 6 ii^ Goat 61 28 26 35 2 2 ta Lamb 59 30 26 37 2 2 6 POULTRY PRODUCTS: 0 ^^^ 34 26 7 47 8 II >? Chicken 34 26 7 40 21 5 0 Duck 27 (20) (5) 42 24 7 "^ Goose 30 (22) Ç) 57 8 5 Turkey 30 23 6 46 22 4 FISH PRODUCTS: 0r' Cod-liver oil 15 12 2 26 59 q Eel 24 18 2 38 38 Halibut-liver oil 20 15 2 34 47 9 Herring 20 12 I 20 60 ÍÓ Menhaden 25 16 3 16 4 55 Salmon 16 12 2 27 55 <^ Tuna 26 19 4 26 48 ? Whale blubber 27 16 2 37 36 S FRUITS, VEGETABLES, NUTS: '^ Co 9 7 2 70 21 ii^ Avocado 22 20 2 50 15 13 Beechnut 9 < 5 4 57 33 § Brazil nut 21 14 6 50 28 Cashew 18 6 II 73 8 Coconut 91 10 2 7 I ^ Filbert () 6 2 2 56 17 21 •^ Hickory nut 8 6 I 72 19 tb. Olive 12 9 2 80 7 Q Peanut 12 46 b 23 5 30 Co 8 6 I 70 21 10 8 2 69 20 , black 6 4 2 37 50 7 Walnut, English 7 5 2 16 65 12 GRAINS, WHOI-E: Barley (14) 7 3 26 44 (6) Corn, white 12 9 I 37 47 Í Millet, foxtail 33 II 15 23 38 6 Oats, rolled 23 13 4 33 43 I Rice 19 13 2 42 38 I Sorghum 12 7 5 40 47 I Wheat 16 12 4 28 48 6 SEPARATED FATS AND OILS: Butter 59 27 12 35 3 3 Cacao butter 59 ^i 35 38 2 I Corn oil 12 8 3 30 55 3 Cottonseed oil 26 23 2 22 51 I Lard 40 32 8 48 11 I Linseed oil 10 (8) (2) 22 18 50 27 22 fSo 9 3 g 4 Olive oil 12 9 2 80 48 41 5 42 8 2 19 8 6 50 31 Shortening, hydrogcnated. 15 7 68 8 Safflower oil 't 3 4 15 76 I 15 9 5 40 44 I 18 9 6 21 55 6 12 6 21 66 I 5 CO 86 YEARBOOK OF AGRICULTURE 7959 A report on one national group estimated to supply about 44 percent continuing in the same environment is of the Calories from fat. of interest in reference to the effect of This fat was calculated to contain occupation and physical activity. A on the average about 42 percent satu- study of clinical cases of British men rated fatty acids, mainly stcaric and in their sixties revealed that the palmitic, 43 percent oleic, and 10 per- coronary disease in those in all seden- cent linoleic. These estimates of fatty tary occupations combined was twice acids were partly substantiated when as frequent as in those who engaged a composite sample of fats fairly in much activity and was three times typical of the proportions consumed in as frequent in those sedentary occupa- 1955 was found by laboratory analysis tions characterized by severe emo- to contain 40 percent saturated fatty tional demands—that is, by a com- acids, 46 percent oleic acid, and 9 bination of emotional stress and percent linoleic acid. limited physical activity. Thus John Dryden's advice in 1680 FAT FROM MILK and dairy products, echoes almost 300 years later: beef, veal, and lamb in 1955 furnished 56 percent of the saturated fatty acids "By chase our long-iivcd fathers earned their and only 10 percent of the linoleic, a food; Toil strung the nerves, and purified the ratio of almost 6 to i. Pork, margarine, blood; and shortenings furnished 30 and 32 But wc, their sons, a pampered race of men, percent of each, respectively, or about Are dwindled down to threescore years and equal shares of saturated and linoleic ten. acids. "Better to hunt in fields, for health unbought, Salad oils furnished only 3 percent of Than fee the doctor for a nauseous draught; the saturated and 28 percent of the The wise, for cure, on exercise depend; linoleic, a ratio of nearly i to 10, or God never made his work, for man to mend.'' more than the reverse of the'first group of foods. Although elevated blood cholesterol The sources of fatty acids varied is often associated with atherosclero- characteristically with the four regions sis, the nature and extent of the rela- of the country—Northeast, North Cen- tionship remain to be defined. tral, West, and South. Not all persons with atherosclerosis The Northeast had the highest pro- or coronary disease have high blood portion of total fat (39 percent) from cholesterol. Conversely, not all persons fats of ruminant animals, and the with high blood cholesterol have car- lowest (28 percent) from pork, mar- diovascular disorders. Nevertheless, garines, and shortenings. continuing high blood cholesterol in- The South was at the other ex- dicates a disturbed metabolism and is treme—lowest (29 percent) in fat from undesirable, whatever the factors ruminant animals and highest (40 involved or the likely ultimate percent) from pork, margarines, and consequences. shortenings. A statistical analysis by the Public DIET has held the attention of sci- Health Service showed regional differ- entists as well as laymen because it is ences in death rates in 1950 from heart one of the contributing factors in the disease, including coronary, with the formation of cholesterol. Northeast highest, 263 deaths per How well do diets in this country 100,000 and the South lowest. 169. measure up to some of the evolving concepts of desirable kinds and quan- OTHER DIETARY factors should not tities of fats in diets? be overlooked. Average diets reported by house- The South had the lowest dietary holds in this country in 1955 were protein (113 grams) compared with FATS AND FATTY ACIDS 87 Percentages of Fat from Different Sources

Household consumption^ ^955

North U.S. Northeast Central West South

Milk, dairy 25 29 28 25 19 Beef, veal, lamb 14 17 16 17 10 Pork, bacon, lard 24 17 21 17 35 Margarine, shortening...... 13 11 12 14 14 Oils, salad dressings 6 6 5 7 6 Poultry, fish, eggs 6 7 6 7 6 Bakery goods, nuts, et cetera.... 12 13 12 13 10

the West, where the protein consump- min E, pyridoxine, and other impor- tion was highest (129 grams), and a tant nutrients. death rate of 217. Also, the South had Also noteworthy is the upward trend far more Calories from grain products, in the proportion of dietary fats from iî3355 compared with the low of 941 meats and milk and the higher intake in the Northeast. of animal proteins. The influence of nondietary environ- Observations, such as these from sev- mental factors with reference to prob- eral population surveys, present strong able sedentary occupations and emo- challenges to basic research to find out tional stresses of urban life, however, which dietary components are supple- was in the same direction as the die- mentary and which may be antago- tary factors noted. The Northeast had nistic to normal fat metabolism in the the highest proportion (79 percent) of long run and what are the zones of de- its population in towns of 2,500 and sirable limits for each. over. The South had 49 percent. Elsewhere are described the shifts in CALLIE MAE COONS is Director of the consumption of foods in the United Research Division oj the States during the past half century. Department of Agriculture. She has en- Of particular interest is the longtime gaged in or supervised Jood and nutrition re- downward trend in the use of fat (a 30- search in the University of Chicago^ the percent decrease in 50 years) and in University of Indiana^ and Oklahoma State the use of grain products, of which we University. Her publications of original re- now eat more in the highly processed search have been in the field of human metab- forms that are lower than natural olism. She taught home economics subjects in grains in unsaturated fatty acids, vita- colleges and universities for some 20 years.

One of the greatest mysteries of life is the Development, growth and vital capacity all power of growth, that harmonious develop- depend upon the availability of food in ment of composite organs and tissues from proper amounts and proper qualities.— protoplasmic cells, with the ultimate forma- RUSSELL HENRY CHITTENDEN. Quoted tion of a complex organism with its orderly in the Journal of Home Economics, adjustment of structure and function . . . February 1957.

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