Sources Of Body Fat

Twenty per cent, of the normal weight of the average man is fat. It is, however, only in small part derived from fatty food. Its chief source is carbohydrate food. Proteins also produce a part of it.

Uses Of Body Fat And Fat Food

Most of the fat that is eaten is rapidly oxidized and supplies much of the heat generated by the living body. Because it is so rapidly utilized for heat-production it saves the living tissues in part from waste. It also contributes a little to the formation of tissues. Tissue waste is most rapid under a protein diet. For these reasons a moderate ingestion of fatty foods makes it unnecessary to eat so large a quantity of protein as would otherwise be needed to furnish energy and contribute to the growth and repair of tissues. Fat is, therefore, sometimes said to be a protein saving food.

The accumulation of fat in the tissues has little to do with the ingestion of it. It is in them a store of potential energy, and may be drawn upon when the food supply is deficient or defective. When present in the subcutaneous tissues it gives rotundity and often beauty of form, both of which are absent when the muscles are unpadded. It also preserves the heat of the body by preventing too rapid cooling.

Digestion Of Fatty Food

When eaten, fat undergoes no digestive change in the mouth but when it is taken in the form of a fine emulsion, as in milk and yolk of egg, a ferment formed in the stomach can split it into its components. When it occurs in cooked meat, it is set free in the stomach in the form of large oil globules, because the gelatinized connective tissue that holds it is then dissolved. In certain forms of indigestion it is decomposed in the stomach and fatty acids are set free. They are irritating to the viscus, and may excite local inflammation. Such decomposition is due to the growth of certain micro-organisms that enter the stomach with the food. It is in the intestines that fats and oils are modified by digestion and are prepared for absorption. The pancreatic ferment steapsin decomposes them into fatty acids and glycerin. The presence of fatty acids in the small intestine gives its contents a faintly acid reaction, although the first effect of the alkaline secretion of the intestine is to neutralize the acids of the chyme from the stomach. Formerly it was taught that the fatty acids help to facilitate the emulsification of the remainder of the oils and fats of the food, and that from the bile, pancreatic juice, and succus enter-icus an abundance of sodium carbonate is obtained. The sodium unites promptly with the fatty acids to form soap, and carbonic acid gas is set free. The soaps thus formed, and the agitation that intestinal peristalsis gives to the contents of the alimentary canal, afford the conditions needed for the making of an emulsion in which form is was believed to be absorbed into the lacteals. Sodium makes, with fatty acids, soluble soaps, but magnesium and calcium also form soaps in the intestines that would be almost insoluble were it not for the bile, which is able to dissolve them. It is now believed that most of the fat in the intestines is split into glycerin and fatty acids and the latter is held in solution by the bile.

In pathologic states, when bile is secreted in insufficient quantity or its entrance into the intestines is prevented by a calculus or other obstruction of the common bile-duct, fatty acids are very imperfectly dissolved and most of the fat then eaten appears in the stools saponified or undigested. When the pancreatic juice is deficient or absent, the same disturbance of digestion is observable. Inflammation of the duodenum may also delay fat digestion, but not to the same extent as results from the failure of bile or pancreatic juice to reach the intestine.

Fats are not absorbed until they reach the intestine, and are taken up almost exclusively from the small intestine, the wall of the large bowel absorbing an inconsiderable quantity. The epithelial cells covering the villi of the intestine play an important part in the absorption of fat. Fatty acids and glycerin are taken up by these cells and are recombined by them into fat granules, which are excreted in turn into the lacteals. The abdominal lymphatics collect the fat thus properly synthesized for the use of the human body and finally empty it into the general blood-current.

The fat in the blood is oxidized chiefly in the most actively metabolic tissues of the body. Possibly a small amount may be oxidized in the blood itself, and another small amount may be deposited as reserve in fat tissues. It might be supposed that the epithelial cells of the intestines when they recombine fatty acid and glycerin would fashion the fat into that peculiar to the body of which they are a part, but this is not altogether true, for when rapeseed oil and mutton tallow which can be easily detected have been fed to animals, they have been recovered again from the fat stored by the animals in their own tissues. The end-products of fat metabolism are carbonic acid and water; these are excreted by lungs, skin, and kidneys.

Butter and cream are the most agreeable forms of fatty food. Bacon, when hard fried, is digestible and well relished by many persons. Cod-liver oil is not agreeable, although a fondness for it is sometimes acquired. It is, however, easily digested. Even if one does not become fond of this oil, he soon learns to tolerate it.

Of fat meats, fat pork is least digestible and fat mutton is less digestible than fat beef.

Artificial emulsification has been resorted to in order to make fats and oils more digestible. It is doubtful if such emulsions accomplish their purpose. Certainly the cruder ones, made by mechanical processes or by simple suspension of an oil in fluids thickened with gum arabic, sugar, and other viscid substances, do not aid digestion. An emulsion made with pancreatic extract may do so.

Too much fat in the food leads to abnormal production of fatty acids and consequent indigestion. Of all common articles of food, fat must be used most sparingly and most judiciously.

Fats and oils are especially to be limited in amount whenever one has indigestion. They are likely to cover the mucous membrane of the stomach and particles of food, and so to hinder secretion by the peptic glands and interfere with the attack of foods by the gastric juice after it is formed.

When digestion is good, a limited quantity of fat can be digested and is most wholesome. Satiety is reached more quickly by its use in increasing amounts than by protein or carbohydrate foods. In general, animal fats are better tolerated than vegetable oils. Hot fats are usuallly less digestible than cold fats. For this reason many persons find it difficult to eat hot mutton and pork, but digest them when eaten cold. Fried foods are not so digestible as foods cooked in other ways, and should be forbidden absolutely for invalids, and but rarely be employed by persons in good health, as these foods are difficult of digestion, and thus lead to dyspepsia and even to disease of the digestive tract. All fats, except limited quantities of butter and cream, should be forbidden in acute diseases of the stomach, intestines, and liver, and in most of the chronic ones. Their use should be closely limited in the presence of gall-stones and when there is a tendency to acne or urticaria.

On the other hand, fatty food must be prescribed for children with rickets and for all who have diabetes. In the latter disease, it partly replaces the carbohydrates, which cannot be used. Fat may be prescribed with benefit in chronic wasting diseases, such as tuberculosis, and during convalescence from severe acute diseases. The most agreeable and digestible forms should be used. At first small portions only should be taken and the quantity be increased as tolerance is acquired.

In a general way fats and oils are laxative, and consequently are useful for those who are constipated, and equally harmful for those who have a tendency to diarrhea.

Most articles of food contain a varying amount of fat and oil. For instance:

The animal fats most commonly used, aside from what is contained in meats, are butter, cream, eggs, lard, suet, tallow, oleomargarin, butterin, and cottolene. These may all be used in cooking or as adjuvants to foods, but they must be employed sparingly by most persons. The vegetable fats that are most used are olive oil, cotton-seed oil, linseed oil, cacao-butter, the oils of various nuts, especially cocoanuts, peanuts, and almonds. Cod-liver oil not only is a food, but contains some medicinal properties, probably chiefly due to the iodin and other inorganic elements that it contains; and possibly also to certain organic derivatives of the liver that resemble alkaloids. Cod-liver oil is used whenever it is desirable to administer fats in as large an amount as possible, and when only the most digestible forms can be given. A tolerance of it is soon acquired by children, even by infants. Adults are rarely able to take it in sufficient quantities to make its use of much importance. It is given to adults in doses of one or two tablespoonfuls three or four times daily, commencing with much smaller doses. To disguise its taste it is frequently given as an emulsion that is flavored with winter-green and other aromatic oils, or it is mixed with malt extracts. If the taste is disagreeable, it is best given in elastic capsules. The clearest oils are the best and are most easily taken. A pinch of salt taken before and after the oil often makes it palatable. It can also be floated in strong coffee or peppermint water, and so swallowed as scarcely to be tasted. Preferably it should be taken clear and swallowed quickly; a little salt or a dry cracker may be eaten afterward to remove the taste from the mouth.