LATENT energy is just as surely found in foods as in wood and coal. Like them, foods are only waiting to be oxidized that they may be converted into heat and energy. The fuel value of foods is expressed in heat units. This is determined by their oxidation outside the body in the apparatus known as the bomb-calorimeter.
The calorie is the unit measure of heat used to denote the energy-giving power of food, and is equivalent to the amount of heat necessary to raise the temperature of one kilogram of water one degree centigrade, or about one pint of water four degrees Fahrenheit. The following general estimate has been made for the energy furnished to the body by one gram of each of the different classes of nutrients :
1 gram protein yields 4 calories of fuel value.
1 gram carbohydrate yields 4 calories of fuel value. 1 gram of fat yields g calories of fuel value.
Bulletin No. 142, United States Department of Agriculture.
By the figures at the right of the chart is represented the total number of calories, or food units, contained in one pound of the various foods under consideration, the building material (protein) being represented by the diagonal lines, the fats by the dotted space, and the carbohydrates by the crosshatching.
From this chart, it will be seen that the most abundant element of grains, legumes, fruits, and vegetables is carbohydrate, while fats predominate in the nuts, protein also being large; and that protein is the chief element in animal flesh, fish, and eggs, there being no carbohydrate at all in these. The carbohydrate of milk consists of milk sugar, no starch being present.
Careful experiments have demonstrated that the body is best sustained in health, strength, and endurance by a diet containing a proportion of about one ounce of protein to nine ounces of carbohydrate and fat. In an approximate day’s ration of 3,000 calories, 10%, or about 300 calories, should be protein. The remainder, or 90%, may be divided, according to individual need or personal preference, between carbohydrates and fats, provided some of each is used. About 25% of fat and 65% of carbohydrate is considered a good proportion. As to the protein requirement in a day’s ration, a well recognized authority on the subject has the following to say :
“Foods should be so selected as to give the ration the right amount of protein, or repair foods, on the one hand, and of fats and carbohydrates, or fuel foods, on the other. A certain amount of protein is absolutely essential. . . . The right proportion of protein has been the subject of much controversy. According to what are regarded as the best investigations, it is generally about 10% of the total number of heat units consumed. This does not, of course, mean 10 %, of the total weight, nor 10 % of the total bulk, but 10 % of the total nutriment ; that is, ten calories of protein out of every one hundred calories of food.
“Most persons in America eat much more protein than this. But that ten calories out of every one hundred is not too small an allowance is evidenced by the analysis of human milk. The growing infant needs the maximum proportion of protein. . . . Consequently an analysis of human mothers’ milk affords a clue to the maximum protein suitable for human beings. Of this milk, seven calories out of every one hundred calories are protein. If all protein were as thoroughly utilized as milk protein or meat protein, seven calories out of one hundred would be ample; but all vegetable proteins are not so completely available. Making proper allowance for this fact, we reach the conclusion that ten calories out of every one hundred are sufficient.” “How to Live,” by Professor Irving Fisher and Lyman Fisk, pages 36, 38.
The fact that protein is absolutely essential for the growth and repair of the body there being no other food principle that can take its place in furnishing muscle-building material has a tendency to lead people to believe that they might be benefited by the consumption of large quantities of protein foods, when the fact is that the body can use but a limited amount for the development and repair of tissue.
Proteins cannot be stored up in the body for future use, as can the carbohydrates and the fats; therefore any excess of protein must be eliminated, at great expense to the vitality of the system. Flesh meat is very high in protein, and contains no carbohydrate. Notwithstanding this, many persons have been accustomed to look upon flesh meat as the backbone of the meal, thus increasing the danger from excess of nitrogenous material. In the vegetable kingdom, the food elements are so combined that the protein aver-age is low. In other words, when we combine the nutritious grains with the bulky vegetables, or the juicy fruits with the concentrated pecan or walnut, the diet is already balanced.
Although protein, when oxidized in the body, is capable of yielding a certain amount of heat, it is inferior for this purpose to carbohydrates and fats, because, on being burned in the body, it also yields certain deleterious products, which throw upon the liver and the kidneys an unnecessary amount of labor, thus weakening them and rendering them more susceptible to the attacks of disease. Many of the ailments so prevalent to-day, such as rheumatism, gout, gastrointestinal disturbances, indigestion, and liver troubles, have been found to be closely associated with the habitual overeating of protein foods.
We would not, however, recommend the measuring and weighing of the foods eaten, in order to be sure of exact proportions. If natural, unprocessed foods, containing all their mineral salts and essential vitamines, are eaten intelligently, with regularity in meals, the calories will take care of themselves.