A food may be defined to be a substance which, after introduction into the body, supplies material for the renewal of its tissues or sustains some of its vital processes. Foods vary greatly in their properties as restorative or constructive agencies, some containing but few essential properties, while others combine almost all of the elements required. As some foods contribute elements for tissue restoration, others are specially concerned in the calorifacient activities of the organism,[948] while others are marked in their tendency to take part, almost exclusively, in special chemical processes.[949]
The various articles used as foods contain nutritive elements combined with innutritious substances. They have been variously classified, but are conveniently divided into
| I. Organic foods, | { | a. Nitrogenous (C.H.O.N.). |
| b. Non-nitrogenous (C.H.O.), | { | Oleaginous Carbohydrates. |
| II. Inorganic foods, | { | a. Water, H2O. b. Saline substances. |
Nitrogen enters largely into the composition of the body, and hence must be abundantly supplied and in combination.
Of the non-nitrogenous elements the most important are fat, sugar, and starch.
The inorganic principles are essential to the process of nutrition. Water, constituting 87 per cent of the bulk of the body, is demanded in constant supply; while the saline substances are necessary for the perfect performance of many of its chemical processes.
It is apparent that no single element can alone carry on the nutrition of the body, and hence variety in the supply of food, as well as sufficiency in its quantity, is essential to normal nutrition. Nor are these the only factors in this complex problem. Proper preparation of food, its supply at necessary temperatures,[950] and other requirements enter into the question of normal or sufficient alimentation.[951]
Alimentation is sufficient when it is so regulated that all the functions of the body are performed in a complete and regular manner. Insufficient alimentation induces a series of phenomena and a result which have been designated “inanition,” or “starvation.”