CHAPTER XIV FATS AND OILS General Considerations: Fat and Oil Substances; Sources of Fats; Chem- Animal Fats: Varieties: Butter, Lard, Suet, Oleomargarine, etc. Vegetable Fats: Value of Vegetable Fats; Absorption of Vegetable Oils; GENERAL CONSIDERATIONS Fats and oils may be divided into two general classes: (a) fixed oils and fats, (b) essential or volatile oils. The former are derived from two sources, i.e., the animal and vegetable kingdoms; the latter are volatile constituents of plants and may be obtained unchanged by the application of heat. They are important constituents of spices and a fuller consideration will be found under the chapter "Spices and Condiments." Fat and Oil Substances.-Fats and oils contain substances of an extremely varied nature. They are devoid of nitrogen and consist almost entirely of three elements, viz., carbon, hydrogen and oxygen; the latter in small proportion, but so combined that they readily undergo oxidation, during which they give out considerable heat. The sugars and starches contain oxygen and hydrogen in such proportions that when their molecules are split up, water (H2O) is formed. In the group of fats oxygen is present in insufficient quantity to produce water with all of the hydrogen atoms, so that combustion takes place with the liberation of heat. It is the peculiar property of hydrocarbons to unite readily with oxygen and it is the consequent development of heat that renders them. so exceedingly valuable as a source of fuel for the animal economy. Sources of Fat.-Fat forms the bulk of butter, fat meat, suet, lard, oils and other fatty substances. About one-sixth of the entire body weight is composed of fat, while only about one-quarter of an ounce is contained in the blood. In a prolonged fast or death from starvation ninety per cent of the body fat is consumed. The chief sources of this supply of fat in the human body are starches and sugars, but not all, as some of it, as Monk has demonstrated, is undoubtedly derived from fatty food. Many of the fatty substances are important constituents of foods, while others, differing only very slightly in chemical composition, are of value, from a commercial standpoint, in the manufacture of soap, candles and paint. Fat is a source of energy, as is evident in the inhabitants of Polar regions, whose aliment is almost entirely fat and oils. Many of the animal oils, such as whale oil, seal oil and fish oil, are obnoxious to the taste of civilized peoples. For the most part the vegetable oils when properly refined make wholesome, palatable food products. Vegetable oils are derived, principally, from the seeds of plants, extracted by pressing the ground or mashed seeds. Animal fats are secured from animal tissues by a process of "rendering" which consists in placing the fatty substances in a large vessel and applying heat until the fat is melted, so that it can be separated from the animal tissues. The animal tissues containing the greatest proportion of fat are the bone marrow, subcutaneous and intermuscular tissues around the various internal organs and the omentum of the abdominal cavity. Chemical Characteristics. Chemically considered, fats are glyceryl esters of fatty acids. The fatty acid radical replaces the OH in the alcohol molecule (glycerin) and joins the alcohol radical CH, or allyl, which is a trivalent ion, whereby fats are formed. By some authorities fats are considered salts of the higher saturated or unsaturated fatty acids in which the glyceryl acts as the base. Just as nitric acid when acted upon by caustic soda forms water and sodium nitrate, so stearic acid will theoretically combine with glyceryl, producing glyceryl stearate, that is, ordinary stearin. Stearin is abundant in hard fat; it is a stearopten solid at ordinary temperature. Fatty Bodies. Fatty bodies are component parts of the cells of animals and plants, more particularly in animal fat, though to some extent in the seeds of vegetables and fruit. The most common are palmitin, olein and stearin and the most common fatty acids are palmitic, oleic, stearic, butyric, caproic, caprylic, rutic and valeric, but there are others. Fat is formed by their union with glycerin. FLUID AND SOLID FATTY BODIES.-The three fatty bodies, olein, palmitin and stearin, form the fat of animal tissues. Olein and stearin are in such proportion that the fat remains fluid if kept at the temperature of the human body. The physical condition of fat or oil, i.e., whether it is a solid or a liquid at ordinary temperatures, depends largely upon the proportion of saturated or unsaturated glycerids present. Fats predominating in a greater proportion of palmitate and stearate are solid, while those predominating in oleate are liquid. Recently a process has been commercialized for saturating unsaturated glycerids by merely heating them with hydrogen in the presence of a catalyptic agent, nickel. Instead of having a white solid similar to tallow, we have a liquid cottonseed oil which is high in glyceryl oleate and low in stearate. This process changes a large portion of the oleate to stearate, thereby solidifying the liquid product. Importance of Fat.-Fat is the most important representative of the hydrocarbon group of foods; common forms are fat meat, butter, cream, a part of milk and cheese. Fat meat, such as beef, mutton and pork, are important ingredients of our diet. As a rule the fat is so closely associated with the lean that it is taken more or less incidentally along with the proteins of the lean meat. The quantity of fat ingested can be regulated by inspection and more accurately determined by the actual separation and weighing of the fat. Meat fats should be thoroughly cooked in the presence of moisture, if they are to be easily digestible (see Volume II, chapter on Scientific Cooking). ASSIMILATION OF FATS.-Fats are comparatively easily assimilated. They pass through the mouth and stomach unchanged. During the digestive process the slight framework of the connective tissue of meats and the protoplasm of cells are peptonized. The enclosed fat or oil globules are liberated and later on emulsified and saponified by the action of the mild but copious carbonates in the small intestine, together with the ferment action of lipase (steapsin). The combined action of these digestive agents changes the fat into an emulsion and eventually saponifies it, thus releasing the glycerin of the fat molecule and reducing the fat to soluble components, soap and glycerin. Other portions of the fat are converted into forms of soap by the action of the pancreatic fluid, a solution of which is quite readily absorbed. A large proportion of the digested fat is absorbed by the lacteals and gains an entrance into the blood by way of the thoracic duct. After a full meal the fluid in the lymphatic vessels, of which the thoracic duct is the largest, is milky from the presence of fat. All the fat does not reach the blood in this manner. A large amount is absorbed directly into the blood vessels in the form of the soluble and insoluble soaps which are manufactured in the bowels. Research experiments have proved that 150 grams of fat (about five and one-half ounces) can be easily absorbed and assimilated with only an infinitesimal loss. As a result it will be good practice to prescribe one-quarter of a pound of fat daily for a diabetic. On watching the blood stream after a meal fat globules can be observed, but after a time the blood resumes its usual appearance. The white blood cells are said to carry these minute fat globules all over the body, distributing them to the working tissues for the production of heat and energy and other current expenditures. The fat itself is reduced to carbonic acid and water which are excreted by the skin, lungs and kidneys. When more food is consumed than is necessary for the immediate needs of the body, fat is stored up in the subcutaneous and other cellular tissues. It is a well-known fact that animals often put on more fat than their food contains. Pigs accumulate much more fat in the body and cows give more fat in their milk than exists in the food which they consume. It is therefore assumed that additional fat is derived from the conversion of proteid and carbohydrate elements, which have already been shown to cause an accumulation of fat, when there is greater consumption of them than is necessary. FAT AS NECESSARY TO HEALTH.-The consumption of fat is required to promote the earlier stages of growth and repair of the organism. There are also many diseased conditions and degenerative changes which are accompanied by increased accumulation of fat in and between the tissues and cells of the body. Therefore it is quite impossible to live very long in perfect health without fatty food. It is equally impossible to live very long upon fatty food alone, since its prolonged use upsets the digestive processes and causes an absolute repugnance for fat. DEPENDENCE OF MUSCULAR ACTION ON FAT.-The expenditure of muscular action is more or less intimately dependent upon fat combustion. It was formerly taught that the force of the body was supplied by the oxidation of nitrogenous materials, for instance, fat eaten with food was believed to be deposited again as fat in the tissues. Of recent years this theory has been exploded and the primary value of fatty foods has been established beyond question as a contributing force in saving other tissues, especially the albuminous, from destruction by oxidation ; whereas its secondary use is in connection with tissue formation. Fats do form a part of many different tisues of the body, even those of the nervous system. FATS VS. OILS.-Both fats and oils employed as food serve essentially the same purpose and may, therefore, be grouped together and considered as a class. Their physical properties are identical, although they differ considerably in their melting points. Fatty bodies and fatty acids vary in chemical composition, but after being absorbed they are recognized mainly in one or two simple forms, chiefly as stearin and olein. While the various fats and oils, of both animal and vegetable origin, have the same beneficial effect upon nutrition, there is considerable difference in their fuel value, and in the facility with which one variety or another may be assimilated in individual cases. Animal fats have a higher nutritive power than those derived from the vegetable kingdom, and of the former, liver fat, butter and cream are the most easily digested, assimilated and absorbed of all fats. The use of fats and oils should be restricted or forbidden in all forms of acute gastro-enteric intestinal disorders, chronic gastritis, dilatation of the stomach, chronic diarrhea, obesity, fatty and waxy liver, gallstones, acne and urticaria. ECONOMY OF FATS AND OILS.-Below is given a table showing cost of 1,000 calories and cost per pound of some of the more common fatty food products. Prices were obtained in New York City in the fall of 1917: Animal Fats. Animal fats are obtained from fatty foods, including butter, cream, suet, lard, oleomargarin, the fat of beef, mutton, pork and bacon, bone marrow, pemmican, fish and cod liver oil. Oil is also obtained from the yolk of eggs. BUTTER.-Butter is one of the most ancient articles of food. It was written of in the Vedas 2000 to 1400 B.C. It is made by churning whole milk, which causes the fat globules of "ripened" cream to coalesce, breaking up the emulsion of cream and forming the butter fat into a solid mass. When cream is designed for the manufacture of butter a "ripening" process is required to bring the cream to a suitable condition. No special precautions are necessary where the shallow pan system at a |