Fats and oils contain three elements—carbon, oxygen and hydrogen. About one-fifth of the body is composed of fat. Before death results from starvation 90 per cent. of the body fat is consumed.

(1) To furnish energy for the development of heat; (2) to supply force; (3) to serve as covering and protection in the body; (4) to lubricate the various structures of the body; and (5) to spare the tissues. The fats and oils used as food all serve the same purpose, and come before the carbohydrates in fuel and force value; in combination with proteids, they form valuable foods for those engaged in severe muscular exercise, such as army marching, mining expeditions, etc.

Fats and oils are but little changed during digestion. The fat is divided into little globules by the action of the pancreatic juice and other digestive elements, and is absorbed by the system. Fat forms the chief material in adipose tissue, a fatty layer lying beneath the skin, which keeps the warmth in the body, and is re-absorbed into the blood, keeping up heat and activity, and preserving other tissues during abstinence from food. Fat sometimes aids the digestion of starchy foods by preventing them from forming lumpy masses in the mouth and stomach, hence the value of using butter with bread, potatoes, etc. The animal fats are more nutritive than the vegetable, butter and cream heading the list. Cooking fats at a very high temperature, such as frying, causes a reaction or decomposition, which irritates the mucous membrane and interferes with digestion.

The principal animal fats are butter, cream, lard, suet, the fat of mutton, pork, bacon, beef, fish and cod liver oil. The vegetable fats and oils chiefly used as food are derived from seeds, olives, and nuts. The most important fats and oils for household purposes are:

Butter, which contains from 5 to 10 per cent. of water, 11.7 per cent. fat, 0.5 per cent. casein, 0.5 per cent. milk sugar (Konig). The addition of salt to butter prevents fermentation. Butter will not support life when taken alone, but with other foods is highly nutritious and digestible.

Cream is one of the most wholesome and agreeable forms of fat. It is an excellent substitute for cod liver oil in tuberculosis. Ice cream when eaten slowly is very nutritious.

Lard is hog fat, separated by melting.

Suet is beef fat surrounding the kidneys.

Cottolene is a preparation of cotton-seed oil.

Oleomargarine is a preparation of beef fat provided as a substitute for butter.

Olive oil is obtained from the fruit, and is considered to be very wholesome; in some cases being preferred to either cod-liver oil or cream for consumptives.

Cotton seed oil is frequently substituted for olive oil.

Nuts contain a good deal of oil.