Students training in athletic sports learn that they must avoid eating too much or they will gain weight and be unable to perform their feats with agility. They also learn what foods are best to develop muscle.
Every one knows that children who are underfed or improperly fed have no energy for work or even play, and that such children are often stunted in mind and body.
Food, then, must have other uses than to please the taste or satisfy the appetite. Important though these uses are, they are merely Nature’s ways to get us to take what we need to keep our bodies strong, healthy, and well developed.
Food is defined as any substance which, when taken into the body, supplies it with heat or energy or builds tissue.
Energy is stored or latent in all organic substances; and when they are burned, the energy is released as heat. Heat is a form of energy.
All foods contain latent energy; and when they are oxidized, produce heat. Their energy then may be used to keep the body warm or to keep up its various activities. In much the same manner the energy in coal heats the passenger coaches of a train and furnishes the power for the engine which pulls the train.
The body in health is maintained at its normal temperature, 98.6° F., even in the coldest weather, by the oxidation or burning of the food taken in, and not by stove or furnace heat from the outside. In cold weather houses are kept warm and warm clothing is worn so that the body will not lose so much heat to the surrounding air. In summer light clothing is worn so that the body will lose heat.
Energy is needed in the body so that the vital processes, such as digestion, respiration, and circulation, may be carried on, and also for work and muscular activity. Though bodily heat and muscular energy are important, they merely result from cell activity. The blood carries oxygen and food to the cells and by the process of oxidation the old cells are burned. To replace them new cells are built up from the food brought by the blood. Cells and tissues must be constantly oxidized, then rebuilt and replaced, because life results in the continual wearing out of the old, and “building up of new tissues, from the food consumed.
Foods are burned or oxidized in the body just as wood or coal is burned outside of the body, except that they burn without flame. They produce, practically, as much heat when burned within the body as they would produce if burned outside the body, and because of this fact we have a means of finding out just how much “heat the various foods yield. The burning of foods and cells in the body is called oxidation and constitutes the vital process called life. The old cells are oxidized and new ones are built up from the food eaten. The foods, by burning, yield heat and energy. Some foods do not contain the substances or elements needed to build tissues, but they will burn in the body and produce heat and energy.
- Foods must contain nitrogen to be able to build tissue.
- Foods that contain carbon will yield heat and energy.