FOODS, COMPOSITION AND NUTRITIVE VALUES OF. 



343 



nary food-materials may be succinctly classified 

 as follows: 



1. Edible Substance : e. g., the flesh of meats 

 and fish, the shell-contents of oysters. 



2. Refuse : e. g., bones of meat and fish, shells 

 of oysters. 



The edible substance consists of 

 1. Water. 2. Nutritive Substances or Nutri- 

 ents. The refuse may, for our present purpose, 

 be left out of account, and our attention con- 

 fined to the edible substance. And, as the wa- 

 ter which forms a part of the edible substance, 

 though indispensable, is nevertheless inexpen- 

 sive and distinct from the nutritive ingredients, 

 we may consider simply the nutrients. 



Speaking as chemists and physiologists, we 

 may say that our food supplies, besides min- 

 eral substances and water, albuminoids, carbo- 

 hydrates, and fats ; and that these are trans- 

 formed into the tissues and fluids of the body, 

 muscle and fat, blood and bone, and are con- 

 sumed to produce heat and force. Viewed 

 from a chemico-physiological stand-point, then, 

 the nutritive ingredients of food can be classi- 

 fied as follows. Of the actually nutritive sub- 

 stances or nutrients of foods the most impor- 

 tant groups (exclusive of water) are 



1. Protein (proteids, albuminoids, etc.) : e. g., 

 albumen ("white") of egg, fibrin of blood, 

 " lean " of meat, gluten of wheat. 



2. Fats : e. g., fat of meat, butter, olive-oil. 



3. Carbohydrates: e. g., starch, sugar, gly- 

 cogen. 



4. Mineral Matter or Ash: e. g., calcium 

 and potassium phosphates and chlorides. 



The terms protein, proteids, and albumi- 

 noids, are applied somewhat indiscriminately, 

 in ordinary usage, to several or all of certain 

 classes of compounds characterized by contain- 

 ing nitrogen. The most important are the 

 proteids or albuminoids, of which albumen, 

 the white of egg, and myosin, the basis of 

 muscle, are types. Allied to these, but occur- 

 ring in smaller proportions in animal tissues 

 and foo;ls, are the nitrogenous compounds that 

 make the basis of connective and other tis- 

 sues. Gelatin is derived from some of these 

 tissues, and may be taken as a type of the com- 

 pounds 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. The mus- 

 cular tissues of animals, and hence the lean 

 portions of meat, fish, etc., contain small quan- 

 tities of so-called nitrogenous extractives crea- 

 tin, carnin, etc. (contained in extract of meat, 

 etc.) which 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 state- 

 ments of the composition of foods. Details 

 regarding the nature and functions of the 

 several classes of nutrients may be found in 

 the article in the " Annual Cyclopaedia " for 

 1881, referred to above. Concerning their 



composition, it will suffice, then, to state that 

 the compounds classed together as protein con- 

 tain carbon, oxygen, hydrogen, and nitrogen, 

 while the carbohydrates and fats contain no 

 nitrogen, but consist chiefly of carbon, oxygen, 

 and hydrogen. The fats are much richer in 

 carbon than the carbohydrates. Animal foods, 

 as meats, fish, etc., contain but little of carbo- 

 hydrates, 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. 



Functions of Nutrients. The different nutri- 

 ents 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. 

 The chief part borne by each in nutrition is 

 shown below : 



f forms the (nitrogenous) basis of blood, 



muscle, connective tissue, etc. 



The protein J is transformed into fats and carbo- 

 oj food I hydrates, and stored as such in the 



body. 



[is consumed for fuel. 

 The fats ( are stored as fat. 

 of food \ are consumed for fuel. 



The carboJijj- ( are transformed into fat. 

 drates of food \ are consumed for fuel. . 



In classifications formerly maintained and 

 frequently met with still, the protein com- 

 pounds were regarde'd as the "flesh-formers" 

 and the sources of muscular energy, while the 

 carbohydrates and fat were looked upon a 

 " fat-formers " and " heat-producers. 1 ' A vast 

 deal of painstaking research, however, has 

 shown that these distinctions were not cor- 

 rectly drawn. The albuminoids are flesh-form- 

 ers, it is true ; indeed, flesh, i. e., muscular and 

 other nitrogenous tissue, according to the near- 

 ly unanimous testimony of the most trustwor- 

 thy experiments, is made from the nitrogenous 

 constituents of the food exclusively. But the 

 balance of testimony is decidedly against the 

 production of muscular energy by nitrogenous 

 compounds exclusively or mainly. Each of 

 the three groups of nutrients probably shares, 

 directly or indirectly, in this function. So, too, 

 it appears that the combustion which produces 

 animal heat is not confined to the carbohy- 

 drates and fats, but the protein compounds, or 

 the products of their decomposition, are also 

 used for this purpose. Again, the production 

 of fat in the body was formerly ascribed to the 

 fats and carbohydrates alone. The view was 

 held at the same time, and is still maintained 

 by some physiologists, that' the carbohydrates 

 can not be transformed into fats, and that a 

 very large part of the fat of the body is formed 

 from the disintegration of the albuminoids. 

 The weight of evidence to-day is decidedly in 

 favor of the assumption that all three of the 

 great classes of nutrients in our foods the 



