The life of this machine can be greatly lengthened by intelligent care, or shortened by neglect and abuse. Its efficiency may be similarly affected. While one cannot hear the pounding of the engine or the rattling of the machinery, yet the machine is damaged if run under too high a pressure and at too great speed.
There are seven classes of the essential elemental food substances,—proteins, fats, carbohydrates, vitamines, salts, cellulose, and water. The ideal diet is one in which these seven elements are regularly supplied to the body in the amounts required to meet its daily needs. A person living close to nature, receiving his food first-handed, direct from nature's health food factory, and eating it with only the cooking and seasoning necessary, and with a reasonable variety, would probably find his diet sufficient, and the elements in about the proper proportions; and with an honest appetite, steadied by a little temperate-in-all-things ballast, he probably would not go far astray as to the proper amounts. But unfortunately, the average individual is not living close to nature. Much that is artificial has come in. Our appetites are capricious, deceitful, and unreasonable. Our foods come to us processed, cartonned, and tinned, often embalmed, devitalized, or adulterated. They are often served to us so disguised that we cannot tell whether their nutritive substance has been concentrated or diluted, or indeed whether or not the body will recognize it as having any nutritive value at all, despite its pleasing flavor. Therefore, in order that the ideal may be approximated to a reasonable and practical degree, we must have some knowledge not only of the needs of the body, but also of these food elements, and how their values may be estimated in the various food substances.
The foods that enter into the make-up of the body and supply its heat and energy are three,—protein, fat, and carbohydrate. While the salts to a certain extent enter into the body structure, they have but little to do with heat and energy production. The remaining food classes are adjuncts, their use being simply to make possible the utilization, by the body, of the tissue and fuel foods. The cellulose assists mechanically in digestion; the water furnishes the necessary fluid; and the vitamines provide the battery, as it were, which sets the whole apparatus in motion.
The Heat Unit
Of the many persons who, for economical or hygienic reasons, have tried to adjust their diet better, some have undertaken the task without a fundamental knowledge of the physiological and caloric value of foods, their composition, or the nutritional needs of the body, and have done themselves more harm than good. It is possible for us to measure the value of our foods, and to express it in terms of heat units; and with a knowledge of the bodily needs, we may supply ourselves with foods in approximately the amounts needed, and in the best combinations. Food oxidized in the body produces the same amount of heat as that burned outside the body, and the instrument by which the heat value of any substance is determined is called a calorimeter. The unit of measure of heat is called the calorie or heat unit.
The calorimeter consists of a double chamber, the outer one containing a given quantity of water. The inner chamber is thus surrounded by a water jacket. In it is placed a definite amount of pure, water-free food to be tested; for example, an ounce of sugar. By means of an electric connection, the sugar is ignited and burned, and the heat produced thereby is imparted to the water in the outer chamber. When the process is complete, the difference in the temperature of the water is noted, and the amount of heat generated is computed. The calorie is the amount of heat necessary to raise the temperature of one pound of water four degrees F., or one kilogram one degree C. In this way, the heat values of pure protein, fat, starch, and sugar have been determined. In the laboratories of the United States government, the composition and caloric value of practically every food substance known has been worked out. Any person can have access to these tables of food values by applying to the government, or by purchasing from almost any bookstore any one of the several books on food values, that are on the market. (See pages 23-27 of this book.)
The heat value of a gram of pure, water-free protein—for example, the casein of milk, egg albumen, or fiber of meat—is a trifle more than four calories. That of pure starch or sugar is also four calories. Fat is more than double this value, one gram yielding nine and three tenths calories. Since an ounce equals about thirty grams, the number of calories to an ounce is determined by multiplying the above figures by thirty. Different kinds of food vary greatly in the proportion of the food elements and also of the water and cellulose they contain. (Cellulose has no fuel value in the human body.) We therefore find a great variation as to their caloric values also. For example, one heaping tablespoonful of home-baked beans will weigh about fifty grams, thirty of which is water and cellulose. Its total caloric value is one hundred, divided among protein fifteen, fat forty (the fat has largely been added), and carbohydrate forty-five. Contrast with this the same quantity of mashed turnips. One heaping tablespoonful will weigh about seventy grams, of which sixty-five is water and cellulose. Its total fuel value is three calories.
By a little study, one may very readily become familiar with the approximate values of the more common foods, and be able to arrive at some conclusion in regard to the correctness of one's daily food ration as to amount and proportions. Many would be surprised to see how far short their diet comes of the ideal.