Humankind digests its food with less expenditure of energy than do animals. It therefore has more energy for other uses. Human beings can do more work and endure more fatigue, also exposure, than any other living creature of similar size because less taxed and occupied with digestion. The human digestive tract is prepared to utilize, not only with relative ease but also relative completeness, edible plant and animal foods.

Though body-constituents and food-constituents are the same, food cannot without change be used by the body. Digestion is the body-process of changing food into the forms necessary for body-utilization. Food to be digested must be made soluble in the body so it can pass through the wall of the blood-vessels into the blood-stream that carries it throughout the body.

Of the five food-constituents two only, mineral salts and water, pass into the blood unchanged. Proteins, carbohydrates, fats, must be changed by the digestive juices and ferments before they can be utilized by the body.

Digestion, the process that produces these food-changes, is effected through the operations of the digestive tract. Though there is more consciousness of food when it is in the mouth than elsewhere there is less happening to it then than later. As it passes down the alimentary tract the digestive activity increases. Food is retained in the mouth only a very short time even when thoroughly masticated, whereas it remains in the stomach from 2 to 5 hours and usually takes about 2 days to travel the entire length of the intestine (12 hours in the small intestine and 36 hours in the large).

Food is eaten at intervals of 4 to 5 hours during the day, and food-waste should be removed from the body once in 24 hours, preferably in the morning after breakfast.

Food-Utilization

The senses of smell and taste, Dr. W. Sternberg insists, recognize chemical changes in food more sensitively than these can be detected with chemical tests. In warmed-over dishes, especially vegetables, some chemical change has occurred. This change renders them less wholesome, he states, for the person that finds them less palatable. Continued loss of appetite leads to some disease of dietary deficiency that is even less easily remedied than diseases caused by overeating, serious as these are. The science of cookery is, he concludes, far more than applied chemistry, physics, and application of heat. It includes applied physiology of the senses, applied aesthetics, and applied psychology, he says, and is a matter of taste in the widest sense of the term.

Digestibility of foods, though differing somewhat for individuals, has been determined in general by artificial digestion (their solubility in chemically produced digestive juices) and experimental digestion (their utilization by the body tested by comparison of food-intake and waste-outgo). The tabulated results are suggestive in selecting dietaries.

Digestibility of Nutrients of Different Groups of Foods and Com-parison of Specific Foods, p. 196; Food-Characteristics as Aids to Digestibility, p. 197; Digestibility of Fruits, p. 44; Tiine of Digestion of Eggs, p. 109; of Animal Foods, p. 196.

Order Of Digestibility Of Animal Foods (After Thompson)

Oysters, eggs (raw or soft-boiled), sweetbreads;

Whitefish (boiled or broiled), as bluefish, shad, weakfish, smelts;

Chicken (boiled or broiled), roast beef (lean), eggs (scrambled or omelet);

Mutton (roasted or boiled), squab, partridge, bacon (crisp);

Fowl (roasted), capon, turkey (boiled); tripe, brains, liver;

Lamb (roasted), chops (mutton or lamb), corned beef, veal;

Ham, duck, snipe, venison, rabbit, game;

Salmon, mackerel, herring, goose (roasted);

Lobster, crabs, pork; smoked, dried, pickled fish or meats.

The meats that digest less readily increase the danger of gastrointestinal disturbance. Delicate, tender meats (porterhouse steak, beef roast, lamb chops, chicken-breast, bird) digest more readily than other meats for persons of imperfect digestion. In skin inflammations, high blood-pressure (due to hardened arteries), rheumatism, and thyroid hypersecretion meat is inadvisable. Meat as it is eaten produces heat in excess of its energy value. It is therefore lessened in summer diet.

Construction of the body (growth), its integrity (health), its regeneration (repair), depend upon food-utilization. If the body cannot use the food eaten it is not nourished. (Food-quantities, pp. 222-223).

Food-proteins are made up of about twenty simpler compounds (amino-acids). All these are not in every food-protein. The food-proteins that contain the compounds that body-protein is made up from are called "complete" proteins (milk, egg-white, meat); others, incomplete (wheat, corn, gelatin). "Complete" proteins maintain the body and promote growth. Of the incomplete, wheat-protein maintains the adult body but does not further growth. Corn-protein alone can do neither. Milk adds what it lacks. It is not nutritively significant whether protein is animal or vegetable, but whether it contains what is needed for body-protein. "A low intake of suitable protein may be infinitely more advantageous to nutrition than a surfeit of an 'incomplete' protein." (Mendel).

Food-fats differ in body-use. Butter-fat, egg-fat, cod-liver-oil fat further growth. Lard, olive-oil, cottonseed-oil do not promote growth.

Food-carbohydrates and fats are used by living body-cells in increased quantity when present in large amounts, hence obesity from overeating.

Food-salts differ in foods, also in body-function. If calcium is absent from the blood excessive nerve-irritability results. Food-salts are imperatively needed for body-structure and regulation of body-function. (Children need lime in food for bone-growth. The aged need food with little lime because it hardens arteries).

Lime In Foods (From Aron's Table)

Too much fat or carbohydrate in food, too much food, or too little, or excess of carbon dioxid causes loss from the body of such food-salts (alkalies). Such loss produces acid-intoxication.

Note: Meat, egg-white, grains, bread, potatoes, lack lime.

The operations of the body are delicate in their mechanism and the body most sensitive to minute quantities of many substances. (Epi-nephrin is present in 1/100000000 Part in blood but is necessary to life).