Fats and Fatty Acids

Fats and Fatty Acids GALLIE MAE COONS FATS often have been prized of processed foods, from roasted nuts articles of diet in man's struggle to main dishes. for food. From early times they Our total and proportional con- have denoted prosperity and hospi- sumption of fats and oils 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 oil with the prophet. the scrutiny of economists and scientists. Scientific and economic concern Fat 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 meats, grains, cottonseed, soy- mated at 32 percent of the Calories in beans, peanuts, olives, and coconut. 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 meat 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 percent 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 carbohydrate 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 pork 38 to 42 percent of Calories from fat, products; 14 percent from beef, veal, 45 to 55 percent from carbohydrates, and lamb ; 13 percent from margarines and 13 to 15 percent from protein. and shortenings; 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, fish, 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 milk noted for household diets and retail and cheese; 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 nutrients; 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 metabolism 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 butter, shortening, 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 carbons), long- firm—at room temperature. 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, deep frying, 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 melting point of a fat can be al- in milk fat and in coconut oil. 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. temperatures. A pure fat is composed of molecules Saturated fatty acids may be of any of glycerol (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), monoglycerides, diglycerides, 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 acid and lard about 12 percent. Other of which is able to carry 2 hydrogens, animal fats run higher. Most animal but with 3 hydrogens (methyl group) fats and cottonseed oil contain about at one end, and an acid (carlDoxyl) 25 to 30 percent of palmitic acid. 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.

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