Food And Digestion
( Originally Published Early 1900's )
WHY WE NEED FOOD
For Warmth. In answering the question why we need food, we may compare the body with a stove. During life the body is warm—it is filled with the "fire of life." Like a stove, the body consumes fuel, and, as in the stove, oxygen from the air is necessary to burn the fuel for the production of heat. In the stove the air from the draft furnishes the necessary oxygen; in the body, it is the air that is breathed.
For Work. We may also, and more aptly, liken the body to an engine ; for an engine not only consumes fuel and becomes warm but it also does work, produces motion, and runs machinery. In exactly the same way our bodies, consuming food, are enabled to do work. When we climb a hill or run, we are doing work. Even when we rest, our heart engines keep up their work and our breathing movements continue. Throughout life we need food for work as well as for warmth.
For Growth and Repair. The body is, however, more than an engine. Each is constantly wearing out its parts, but the body alone can repair itself. It does this with the food it uses. All day long active boys and girls wear out their nerves and muscles, and this causes sound sleep during which repair takes place faster than wear, and worn-out tissues are built up again. Furthermore, the body can add to itself, for we see the child grow to the stature of a man or a woman.
THE CLASSES OF FOODS AND THEIR USES IN THE BODY
If you were asked to state what kinds of food are consumed in America, you could write a very long list. In all this variety there is, however, a great sameness. Chemists have analyzed the foods and found that they contain only five kinds of sub-stances or classes of foods. This fact is very plainly shown in the tables of food composition.
The Three Chief Classes of Foods. Everyone knows that potatoes, molasses, butter, and lean meat are very different ; and that potatoes and rice are more alike than potatoes and butter. Potatoes and rice are both known as starchy food; molasses contains chiefly sugar; butter consists of fat; and lean meat is chiefly composed of a substance called protein. We have here, then, three classes of foods : (1) sugar and starch, together classed as the carbohydrates;* (2) fats; and (3) proteins.
Almost any food we may purchase is a mixture of two or all three of these classes. Sugar, olive oil, and lard are exceptions. Starch is found with proteins or fats, or with both. From the tables showing the composition of the various foods, 89, 116, 127, 136, 147, 222, and 235), find out what, besides starch, is 'found in corn, wheat, almonds, and beans. Find out what classes of foods occur with proteins in peas, pecans, meat, and fish. Mention three foods that are largely fat.
Uses of the Three Chief Classes of Foods. We have seen that food is needed in the body for warmth, for work, for growth, and for repair. We may state this still more simply by saying that we need energy foods and building foods, for heat and work are simply two forms of energy, and growth and repair are the result of building up the tissues. The question now is, which of the three classes of foods mentioned are energy foods and which are building foods. Carbohydrates, fats, and proteins all furnish energy, since they can all be used as "fuel" in the body. In this respect fats give the most energy, one pound of fat yielding more than twice as much as a pound of carbohydrates or protein.
Proteins,however, differ from carbohydrates and fats in that they serve other needs in the body. They are the only class of foods that can be used for growth and repair. We shall, therefore, use the term building foods in further references to this class of foods. Since the carbohydrates and fats can serve only as the source of heat energy and energy for work, we may refer to these two classes of foods as energy f oods.
Mineral Foods and Water. To the carbohydrates, fats, and proteins must be added a fourth class, minerals, and a fifth class, water. Neither of these latter can furnish energy nor are they of use for growth or repair, but they are absolutely necessary for the health of the body. Of the minerals, table salt is the only one that must be added to our food, the others being present in sufficient quantities in a varied and well-balanced diet in which fruits and vegetables play an important part. Water dissolves food and waste substance in the body, and should be consumed in considerable quantities daily.