( Originally Published 1921 )
The human body and the foods eaten by man are of necessity composed of the same chemical elements, since the one is made from the other. This is strictly true if we class water as a food. Oxygen from the air, while necessary to life, is not found in the body, save in the form of water. The elements composing water, oxygen and hydrogen, are the two most abundant elements composing the living flesh. The next most important is carbon, which we know in coal and also in diamonds, though neither substance is used for food—which is fortunate as they are both expensive. The fourth important element is nitrogen. We do not get it from the air, though it is there in abundance, in the elementary form. Nitrogen, combined with the three preceding elements and very small proportions of certain minerals, forms complex substances known as proteins. Protein in various forms and combined with from two to three times its weight of water, composes all living tissues except fat, and the mineral structure of the bones.
Fat, which is merely stored fuel, is composed of carbon, hydrogen and oxygen. The bones and teeth are chiefly made up of calcium phosphate, a combination of calcium, phosphorus and oxygen.. About ten other chemical elements also enter into the composition of the human body and must, therefore, be derived from food. All of these are minerals, and all are present only in small quantities. Because of the small amount of these minerals needed in the life processes their importance was for a time overlooked. More recent knowledge has shown this to be a grave error. For illustration, iron existing in the human body in proportions of only one part in 25,000, is none the less absolutely, essential to life, since the hemoglobin, the oxygen carrying substance of the red blood corpuscles, must contain iron. The list of minerals includes calcium, phosphorus, sodium, potassium, chlorine, iron, sulphur, magnesium, iodine and fluorine.
We can not learn much of practical worth from the mere statement of the chemical elements present in the body. The reason for this is that few of these elements are of use to the body if taken in their elementary form. We can use in breathing the elementary oxygen of the air, but the body can make no use of nitrogen, even more abundant in the atmosphere. Carbon, iron and sulphur (and so on through the list), are examples of chemical elements that are of no use to the body in their simple uncombined form. Most of these food minerals cannot he utilized, even in their compounds, unless these mineral compounds or salts have previously been incorporated with the more abundant organic elements. This combination of minerals with car-bon, oxygen, hydrogen and nitrogen, which takes place in plant life, makes it possible for animal life, including man, to exist. Without the existence of plants all higher animal forms would perish. We, therefore, live on second hand food, which has gone through one life cycle. The carnivorous animals go a step further and secure their food elements third hand, through the previous life processes of plants and other animals.
Man can exist either by this second hand or this third hand process, or a combination of the two. Human food, composed of the substance or products of plant or animal life, is generally classified by the chemist as "organic," as distinguished from inorganic or mineral substance found in the earth. Man can utilize a few in-organic substances, of which air and water are the chief. He can also make limited uses of a few minerals in their inorganic form, such as common salt. But for the most part man depends upon organic food and can not utilize elementary or mineral substances.
As the various substances formed by the combination of chemical elements are exceedingly numerous, early food chemists attempted to classify them into a few groups and so simplify matters. The group names so chosen were "protein," "carbohydrates," "fat" and "ash," or "mineral salts."
Protein, as already explained, is the name not for a single substance, but for a large group of chemical substances, the essential similarity of which is that they all contain the chemical element nitrogen. In the early work of food analysis no effort was made to determine the exact nature of these proteins. In fact, the analysis was usually made merely by determining the amount of nitrogen present and calculating from this the amount of protein, on the assumption that proteins usually contain about sixteen per cent of nitrogen.
Two errors were made by the early food chemist in regard to protein. One was that of attaching undue importance to it as a food substance, and the other was in assuming that one protein was as good as another. The first assumption was only natural, as the body is composed chiefly of protein; hence it seemed that protein should be the most valuable food, and that its use in larger quantities would lead to better nourishment. This proved to be an error because it was not fully realized that the chief function of food in the body was that of a fuel to produce heat and energy. For a rough illustration, we might liken the body to a boiler and engine that served the double purpose of heating the building and supplying power. The boiler and engine are made of iron. The fuel required is carbon (coal). Attempting to fire the boiler with iron would be absurd. Novi the human boiler-engine can, in fact must be supplied with a limited quantity of the material of its construction, as it has the power of constructing itself in the growth or the "repair" of its mechanism. But its chief requirement is fuel for the generation of heat and energy.
The second error made regarding this group of substances collectively known as proteins, has led to many serious misconceptions regarding food values. As large quantities of protein were thought to be important, lean meat was formerly very highly rated as a food. The vegetarians, chiefly because of sentimental reasons, disapproved of the use of meat. But they fell into the grave error of assuming the need of so-called "meat substitutes," or vegetable foods particularly rich in protein. We now know that this was a double-barrelled mistake; in the first place we need no meat substitutes because the meat diet contains entirely too much protein to begin with. Secondly, vegetable proteins, particularly those of the legumes : beans, peas, peanuts, etc., are decidedly inferior forms of protein and are only partly utilized by the living organism. This important subject will be considered further in the fourth chapter.
The second group of food substances, chemically considered, is carbohydrates. The chief carbohydrates are starches and sugars. There are several forms of sugar differing only slightly in their chemical composition. Carbohydrates form the bulk (sixty to eighty per cent) of all human diets of vegetable origin. There are no carbohydrates in animal foods except the sugar in milk. Carbohydrates are also the cheapest food substance. Grains are composed of from four-fifths to nine-tenths starch. Corn is the cheapest known food in the central and eastern United States. Wheat in the eastern United States costs nearly twice as much as corn and is still a very cheap food. Wheat at a dollar a bushel, if a man lived on it and ate it straight from the bushel, would make the cost of living less than three cents a day. In some parts of the world, where corn is not grown, wheat is the cheapest food substance. They feed it to the pigs and chickens in Oregon. In China rice, and in India millet are the cheapest foods. In Russia it is rye and in Germany it is potatoes. The potato, chemically, is practically the same as the grains—the difference being that it is in moist form, carrying about three-fourths water by .weight, and being very similar in composition to a cooked cereal porridge, as boiled wheat or corn meal mush.
Without the development of the grains and cheap roots and tubers as the dominant elements of the human diet, the present population of the world could never have existed. These foods must therefore form a great bulk of the total human bill of fare. And this involves constant danger of improper nutrition because carbohydrates, though a good fuel substance for the human engine, do not supply the elements of the body's growth nor for its proper function. Starch and sugar are related forms and contain the same elements. In fact, sugar can be made from starch as is done in the case of glucose, which is a sugar made from corn-starch.
The third general group of food substances is fat. Some fat is essential in the human diet, as the Germans discovered during the war. A certain amount of fat makes the diet more palatable, and most of our modern cookery is based upon the use of fat to "enrich" other food substances. Yet fats and carbohydrates contain the same three elements: carbon, hydrogen, and oxygen. Their sole function in the body is that of being oxidized, or burned in our slow physiological fires, to produce heat and energy. The use of fat from foods to make the human body fat is not a case of physiological use but merely a storing of fuel food for later use. The difference between fat and carbohydrates is in the amount of oxygen present, or the degree to which the hydrogen and carbon have already been oxidized. Because the fat contains less oxygen it is capable of further oxidization, and hence a given amount of fat will create more heat and energy—two and a fourth times as much—as will starch or sugar. For this reason fat is worth more per pound. Oil, at a price of twenty-two cents a pound, is just as cheap as sugar at ten cents.
In a carnivorous diet, the carbohydrates being absent, fat becomes the chief source of body fuel. Protein can also be burned, but it burns waste-fully, leaving an unoxidized residue that must be excreted from the body, chiefly through the kidneys, a process which man is not as able to handle as well as the carnivorous animals.
The remaining group of food substances have variously been known as ash, minerals, or mineral salts. Most of these salts, in order to be available for human nutrition, must be chemically combined with the organic food elements. Thus, sulphur enters into the chemical composition of some proteins, such as egg albumin; phosphorus, on the other hand, is present in some of the fat-like substances of egg yolk. Calcium salts are a fundamental and very vital element in milk. The growth of the young animals, and consequent rapid bone formation, requires a large proportion of such bone-forming minerals. The fact that the calf grows faster than a child results from cow's milk being richer in protein and mineral salts than is necessary as a human food, even for the young. Hence, cow's milk may be diluted, or may form only a portion of the food of the child.
Mineral salts are present in varying quantities in foods of vegetable origin, but the proportion is greater in the leaves or other growing tissues than in those substances like seeds, tubers or pulpy roots which serve the purpose of food storage reservoirs in the plant's life and hence contain large quantities of starch or fat. Green leaves are especially rich in iron; spinach being richest of any known food in iron of a form that may be utilized by the human body.
The usual tables of the chemical analysis of food give the percentage of protein, carbohydrates, fat, mineral salts and water. The pro-portion of the water is, of course, a very important consideration when estimating the value of food by the pound. For illustration, fresh fruit such as peaches contains about eighty-five per cent of water and only fifteen per cent of actual food substance. But dried peaches contain about fifteen per cent of water and eighty-five per cent of food substance. Hence, the latter, ignoring the question of the superior flavor of the fresh fruit, would be worth nearly six times as much per pound. Another illustration to show the importance of considering the water in food, is that of dry versus cooked cereals. A menu giving an item of "four ounces of cereal" if interpreted as the dry cereal, would have at least four times the food elements than if the dish be considered as meaning four ounces of the ordinary cooked cereal porridge.
Tables of food analysis also usually have a column headed "calories per pound." The calory is a unit of measurement taken from the physicist and is primarily a unit of heat. If a given quantity of food contains so many calories, it means that if burned it would give off so much heat. Most of our food is burned in the body; that is, oxidized, with the result that heat is always produced. A certain portion of this heat energy may be transformed into mechanical or muscular energy. But mechanical energy can not be created in the living body, nor in the engine cited so often to illustrate bodily functions, without the producing of considerable heat. That is why we get warm when we exercise.
The use of the term "units of heat" is some-times misleading. Heat and temperature are related but different things. The thermometer measures units of temperature.
A pint of water at a temperature of 100 degrees is twenty temperature degrees hotter than a pint or a quart of water at a temperature of eighty degrees. The number of degrees of temperature are not affected by the amount of water. Heat units do consider the amount of water and a quart of water at a given temperature contains twice as many heat units as a pint of water at the same temperature. It also takes twice as many heat units to raise the quart of water a given number of temperature degrees, and it would take twice as much fuel to heat it.
The human body is always maintained at a temperature very close to 98 degrees. Any departure from this temperature is a serious business—fever temperature rarely rises above 105 degrees.
The heat of the body is supplied by the oxidation or slow burning of the fuel foods. The amount of heat required to maintain the body at its normal temperature of ninety-eight degrees will depend on the temperature of the surrounding air, the amount of clothing, and the size of the body which affects the amount of radiating surface from which heat may be lost.
The evaporation of water absorbs heat very rapidly. And considerable water is constantly being evaporated from the moist surface of the lungs and from the moist skin. The over heating of the body is prevented by the control of the amount of this evaporation. On a hot day, or when generating extra heat by muscular exertion, a man sweats, while a dog or a chicken "pants" to secure this extra evaporation. The degree of relief from this extra evaporation will depend on the humidity of the atmosphere.
The body is kept from getting too cold by the actual stimulation of extra oxidation, but this oxidation to generate extra heat seldom occurs with a man wearing the usual clothing and ex-posed to the usual temperatures. The muscular action of heart, lungs, etc., ordinarily generates ample heat indoors or in hot weather, while out of doors in cold weather we instinctively keep the voluntary muscles active. Man, therefore, seldom needs extra food just to generate heat, as the heat produced during the muscular action is nearly always sufficient, and usually more than sufficient so that the excess must be taken care of by evaporation.
The calory measures the value of the food from the standpoint of its power to produce heat and energy. It takes "calories" to keep us warm and to make our muscles work. Moreover, we measure the fat-forming tendencies of food by calories, because fat in the body is derived from elements which, if oxidized or used as body fuel, would create heat and energy. Bodily fat may be derived either from fat or from carbohydrates or, somewhat wastefully, from protein.
Because the bulk of our food is utilized in creating heat and energy, or if taken in excess is stored as fat, we commonly consider the number of calories in the diet as the unit of measure of the amount of the food eaten. It is a some-what dangerous method of food measurement, because it measures only one essential function of food. Thus out of the daily ration of two pounds of food, eighty to ninety per cent may be utilized in the body for oxidation, and hence be measured correctly by the number of calories, yet the remaining ten to twenty per cent, including the protein, is fully as essential to health and life as the more bulky fuel portion, the measure of which is expressed in calories.
Since fat and carbohydrates are utilized in the body in almost exactly the same way, and the essential value of both may be measured in calories, it was formerly thought that the statement of the number of calories and of the amount of protein was sufficient to give a true conception of the worth of a given food or of a given diet. By these two terms we may measure ninety-eight or ninety-nine per cent of all the weight of the food substance. But the remaining one or two per cent, including the mineral salts and the vitamines, while insignificant in quantity, are still just as vital to life and health as the more than bulky portions. We can even go further and state that a single mineral or a single vitamine, which in quantity may be less than one thousand of the weight of the food, is absolutely essential to life, and if "deficient" in a diet, its lack will cause quite as serious results as if the whole quantity of food was insufficient.
The term "calories" is of value in considering food from the quantity standpoint. We can form approximate ideas of the worth of food per pound in the number of calories it contains. We can also intelligently discuss the total amount of food that should be eaten in terms of calories. But such considering of food quantity is only safe when the diet has first been properly selected and proportioned to make sure of the inclusion of sufficient variety and proper amount of the essential minor food elements. Unless these other factors are first considered the study of food in terms of "calories" is apt to prove a delusion and a snare. Thus "calories" alone will proclaim that one and a half pounds of starch or five-eighths of a pound of oil is a sufficient daily food allowance for a man. Obviously, neither substance, nor any combination of the two substances, would support life; though they would supply heat and energy, they would not prevent starvation because of lack of other food elements. In fact, it has been demonstrated that an animal will starve to death more quickly on such mere "fuel foods" than if undergoing a complete fast. The reason for this is that the process of digestion and the subsequent oxidation of the fuel food consumes the body store of these rarer food essentials and hence results in their exhaustion more quickly than when undergoing a complete fast.
This old-time chemical analysis of food as protein, carbohydrates, fat, mineral salts, and in calories per pound, is still valuable information for those who are also informed of other and more recent aspects of food science. But this mere chemical analysis taken alone is not of much practical use and has doubtless often been worse than useless. A little knowledge is a dangerous thing, and what the analytical chemist can tell of foods by consulting his test tubes and without studying effects on the living body, is only a little of the knowledge of foods that is available for us today.