from their chemical composition, with so near an approach to accuracy that in Germany, where the best research is done, tables, giving in figures the composition and nutritive valuations of foods, have been prepared by eminent chemists and physiologists and are coming into general use. HOW OUR FOOD SUPPLIES THE WANTS OF OUR BODIES. Our food supplies the wants of our bodies in four ways: Food Furnishes, 1. The material of which the body is made. 2. The material to repair the wastes of the body. Food is Consumed in the Body to 3. Produce heat to keep it warm. 4. Produce muscular and intellectual strength for work. To understand how food does its work in the nourishment of our bodies we must recall the fact that our bodies and the materials that nourish them are both composed of a certain list of chemical elements which are combined in a great variety of compounds. These compounds we may divide into three groups: A. Water. B. Organic Compounds. C. Mineral Compounds. About water we need here say very little. Of the mineral compounds, one of the most important is the phosphate of lime which makes the basis of bone. Phosphates, sulphates, and chlorides of potassium and sodium, and other mineral salts likewise, occur in our bodies and are essential not only to health, but even to life itself. But in studying food from the standpoint of its nutritive value, that is, value for supplying bodily wants, we have to do, chiefly, with the organic compounds. These we may roughly divide into three principal classes, and this classification will do for the organic compounds of both our food and our bodies. I. Protein Compounds, otherwise known as albuminoids, flesh formers, or "flesh substance." II. Fats. This division answers very well so long as we are only making approximate estimates of the nutritive values of our foods, but when we study foods very accurately, and more especially when we come to the chemistry of the body, we find compounds which cannot very well be placed in either of these classes. Fortunately for our purpose, however, the proportion of these latter compounds in our foods and in our bodies is very small.* We have not as yet sufficiently accurate analyses to tell in just what proportions these compounds occur in the body. Very probably the body of an average healthy This classification leaves out of account numerous compounds of minor importance, including the so-called "nitrogenous extractives," which are the essential constituents of "extract of meat." See beyond. man, weighing 148 pounds, or with clothing 156 pounds, would contain something like the following quantities: Of course I do not mean to say that this is an exact statement of the amounts of these compounds in the body of any given man or of an ideal man. These figures are simply an attempt to show, in a general way, in about what proportions the compounds probably occur. Such then is the composition of the body. These elements and compounds must come from the food. It is the food that furnishes the material of which the growing body of the child is built up, and as our tissues are being continually consumed by work, and thought, and worry, it is by food that they are restored; and finally it is our food that supplies the fuel by whose consumption the heat and strength of the body are maintained. Viewed from the standpoint of their uses in the nutrition of man, the constituents of ordinary foods may be succintly classified as follows: 1. Edible Substance, e. g., the flesh of meats and fish, the shell contents of oysters, wheat flour. 2. Refuse, e. g., bones of meat and fish, the shells of oysters, bran of wheat. The edible substance consists of 1. Water. 2. Nutritive Substance or Nutrients. Of the meat my butcher sends me, the fish I find in the market, and the other food upon my table, only a part serves to fulfill these purposes. The bone of my roast beef I do not use for food at all, and that of shad is worse than useless, because of the bother it makes me to get rid of it; it is only the edible portion that is of actual value to me as food, the rest being merely refuse. And when we come to consider the edible portion, the meat freed from bone and gristle, the flesh of the fish, or the flour as it is baked in bread, we find that these consist largely of water. And although water is indispensable, that in the meat or the potatoes on my table is of no more value for the support of my body than the same amount in milk, or in the glass of water by my plate. Leaving out of account, then, the refuse and the water, we have the nutritive materials, or, as we may call them, the nutrients of our foods. Speaking as chemists and physiologists, we may say that our food supplies, besides mineral substances and water, three principal classes of nutritive ingredients or nutrients, viz., albuminoids, carbohydrates, and fats; and that these are transformed into the tissues and fluids of the body, muscle and fat, blood and bone, and are consumed to produce heat and force. Let me speak in a little more detail of the compounds of which our foods are composed: Protein, so called, "flesh formers," or "flesh substance."-The terms protein, proteids, and albuminoids, are applied somewhat indiscriminately, in ordinary usage, to several or all of certain classes of compounds characterized by containing carbon, oxygen, hydrogen, and with them, nitrogen. The most important are the proteids, or albuminoids, of which albumen, the white of egg, fibrin of blood, casein of milk, myosin, the basis of muscle, and gluten of wheat, are examples. Allied to these, but occurring in smaller proportions in animal tissues and foods, are the gelatinoids, the nitrogenous compounds that make the basis of connective and other tissues. Gelatin, whence the name gelatinoid (gelatin-like), is derived from some of these tissues, and may be taken as a type of the compound of this class. As these constituents are of similar constitution, and have similar, or nearly similar, uses in nutrition, it is customary to group them together as protein. What we should especially bear in mind, then, is that protein is a term applied to the nitrogenous constituents of our foods, and we shall see these are, in general, the most important, as they are most costly, of the nutrients. The muscular tissues of animals, and hence, the lean portions of meat, fish, etc., contain small quantities of so-called nitrogenous extractives-creatin, carnin, etc.— which are the chief constituents of meat extract. These contribute materially to the flavor, and somewhat to the nutritive effect, of the foods containing them. They are not usually deemed of sufficient importance, however, to be grouped as a distinct class in tabular statements of the composition of foods. Fats. We have familiar examples of these in the fat of meat (tallow, lard), in the fat of milk, which makes butter, and in olive, cotton seed, and other animal and vegetable oils. The fats consist of carbon, oxygen, and hydrogen, and contain no nitrogen. In nutritive value, as in cost, they rank next to the protein compounds. For some of the nutritive functions, indeed, the fats equal or exceed protein in importance. Carbohydrates.-Starch, cellulose (woody fiber), sugar, and inosite ("muscle sugar"), and other similar substances, are called carbohydrates. Like the fats, they consist of carbon, oxygen and hydrogen; but they have less carbon and hydrogen, and more oxygen than the fats. Mineral Matters, or Ash.-When vegetable or animal matters are burned, more or less incombustible material remains as ash. The ingredients which make the ash are called mineral matters, or sometimes, salts. They are, for the most part, compounds of the elements, potassium, sodium, calcium and iron, with chlorine, sulphuric acid and phosphoric acid. Sodium, combined with chlorine, forms sodium chloride, or common salt. Calcium, with phosphoric acid, forms calcium phosphate, or phosphate of lime, the mineral basis of bones. Our bodies, as I have already said, contain scores of compounds, many of which cannot be included in either of the above four classes. But the bulk of the compounds, exclusive of water, in the bodies of animals, as well as those in the food by which they are nourished, may be classed with either protein, fats, carbohydrates, or mineral matters. Animal foods, as meats, fish, etc., contain but little of carbohydrates, their chief nutrients being protein and fats. Milk, however, and some shell-fish, as oysters, scallops, etc., contain more or less of carbohydrates. Vegetable foods, as wheat, potatoes, etc., contain less protein, and consist largely of starch, sugar, cellulose and other carbohydrates, though nearly all contain more or less of fats. HOW THE NUTRITIVE INGREDIENTS OF THE FOOD NOURISH THE BODY. These different nutrients, as we have seen, have different offices in nourishing the body, in building up its tissues, repairing its wastes, and serving as fuel to produce animal heat, and muscular and intellectual energy. Just what is done by each class, exactly how they are transformed and used in the body, is not yet fully known. Still, we have to-day a tolerably fair idea of the principal parts played by each class of nutrients. Suppose that I have for breakfast beefsteak, bread and butter and potatoes. The beef supplies me with considerable protein (in the lean meat) and fat. The butter is nearly all fat. The bread contains a little protein and fat, and the potatoes the same ingredients, but in still smaller proportions, the principal nutrients of both being starch or carbohydrate. A small part of the food passes through the body undigested and constitutes the excretion of the intestines. The larger portion is digested, taken into the blood and distributed through the body, where it does its work, is consumed, and finally given off as water and carbonic acid, by the lungs and skin, and as water, urea, &c., by the kidneys. So then the bulk of the protein, fats and carbohydrates of my breakfast is digested, and, in the course of the day, the larger part of this digested material finds its ways into my blood and is distributed through my body. Part of the protein of the food serves to repair my muscles, tendons, skin and other organs that are being worn out by constant use. The rest is consumed sooner or later, no one knows exactly when, where or how. Part is probably transformed into fat and stored as fat in my body, and thus replaces fat that is consumed to keep me warm and to give my muscles strength for the work they have to do. And probably a part of the protein is changed into glycogen, a carbohydrate which occurs in the liver. Part of the fat of the meat and bread is stored as fat in my body and part is burned, yielding heat to keep me warm and muscular energy as well. The chief use of the carbohydrates, the starch and sugar, of the bread and potatoes seems to be to serve for fuel though they are transformed into fats also. It is a matter of common experience that many people are made corpulent by eating sugar and starchy foods, and grow lean when they avoid then. By comparing the amounts of carbon, oxygen, hydrogen and nitrogen, actually found by experiments to be consumed by different individuals, and also noting the amount and composition of the food of different people, estimates have been made of the quantities of the several nutrients required by individuals of different classes under various conditions. Professor von Voit, of the University of Munich, for instance, who has made more extensive researches upon this subject, perhaps, than any one else, computes that a fair daily ration for a laboring man of average weight, at moderate work, would need to supply 4.2 ounces (0.26 lb.) of protein, 2 ounces (0.12 lb.) of fats, and 17.6 ounces (1.12 tb.) of carbohydrates. Of course he may get on with less of either one, provided he has more of the others. But there is a minimum below which he cannot go without injury, and especially he must not have too little protein. He may have more protein and less carbohydrates or fats with no great harm, but with too little protein he will suffer, no matter how much carbohydrates his food may furnish. CHEMICAL ANALYSIS OF FOODS. Let us, then, notice what chemical analysis has to say of the amounts of the different nutrients in some of our ordinary foods. The tables beyond give results of analyses, the most of which are selected from a much larger number, performed in the FOOD-MATERIAL. chemical laboratory of Wesleyan University, at the instance of the Smithsonian Institution, for the Food Collection of the United States National Museum. The details will perhaps be best explained by an example. The flesh, or edible portion of a specimen of beef sirloin, of medium fatness, was analyzed and found to contain, approximately: water, 60 per cent; protein, 20 per cent; fats, 19 per cent; mineral matters, I per cent. But when we buy our sirloin steak or roast, by the pound, as we ordinarily do, we get not only the flesh, the edible substance, but with it more or less bone, sinew, and other refuse matter. This specimen contained about one-fourth, or 25 per cent. of bone, and only three-fourths, or 75 per cent, of flesh. If, then, we are to consider the composition of the meat as we buy it, we must take the refuse matter into account. The proportions of the several ingredients, in both the edible portion and the whole piece above referred to, are shown in the following table: Refuse, bones, etc. Water Protein Fat.... Mineral matters... Totals......... This very imperfect analysis may be stated in the following form, as is done in the tables beyond: * IN EDIBLE PORTION i. e., flesh freed from bone and other refuse. IN MEAT AS PURCHASED including both edible portion and refuse. Fats. matters. Mineral Refuse bones, etc. Water. Nutrients. EDIBLE PORTION. Beef, sirloin, med. fatness" Pr. ct. Pr. ct. Pr. ct. Pr. ct. Pr. ct. Pr. ct. Pr. ct. Pr. ct. Pr. ct. Pr. ct. Pr. ct. 19 Tables I and II., herewith, give the composition of a number of animal foods, mostly from late American analyses. It is only a short time since analyses of American meats, fish, etc., have been undertaken in any considerable number, and those as yet accomplished are far from sufficient for a complete survey of the subject. Indeed, the work already done can be regarded only as a beginning. Still, the figures will give a tolerably fair idea of the composition of the articles named. Table III. gives analyses of vegetable foods and beverages. The tables contain also columns for carbohydrates, etc., which occur in milk and in some shellfish, but are not found in ordinary meats in sufficient amount to warrant their insertion in such statements as this. |