COMPOSITION OF FOOD AND ACTION OF ENZYMES. 



735 



analyses given by Konig* may be taken as an indication of the 

 average composition of the most commonly used foods except as 

 regards the vitamins, whose presence in the foods cannot be stated 

 in precise quantitative terms. An examination of this table shows 

 that the animal foods, particularly the meats, are characterized 

 by their small percentage in carbohydrate and by a relatively 

 large amount of protein or of protein and fat. With regard to the 

 last two foodstuffs, meats differ very much among themselves. 

 Some idea of the limits of variation may be obtained from the 

 following table, taken chiefly from Konig's analyses: 



The vegetable foods are distinguished, as a rule, by their large 

 percentage in carbohydrates and the relatively small amounts of 

 proteins and fats, as seen, for example, in the composition of rice, 

 corn, wheat, and potatoes. Nevertheless, it will be noticed that the 

 proportion of protein in some of the vegetables is not at all insignifi- 

 cant. They are characterized by their excess in carbohydrates 

 rather than by a deficiency in proteins. The composition of peas 

 and other leguminous foods is remarkable for the large percentage 

 of protein, which exceeds that found in meats. Analyses such as 

 are given here are indispensable in determining the true nutritive 

 value of foods. Nevertheless, it must be borne in mind that the 

 chemical composition of a food is not alone sufficient to determine 

 its precise value in nutrition. It is obviously true that it is not what 

 we eat, but what we digest and absorb, that is nutritious to the 

 body; so that, in addition to determining the proportion of food- 

 stuffs in any given food, it is necessary' to determine to what extent 

 the several constituents are digested. This factor can be obtained 

 only by actual experiments. It may be said here, however, that 

 in general the proteins of animal foods are more completely digested 

 than are those of vegetables, owing chiefly to the fact that the 

 latter may contain a considerable amount of indigestible cellulose, 

 which tends to protect the protein from the action of the diges- 



* See Konig, "Die menschlichen Nahrungs und Genussmittel"; and At- 

 water and Bryant, "The Chemical Composition of American Food Materials,'* 

 Bulletin 28, United States Department of Agriculture, 1899. 



t Atwater, "The Chemistry of Foods and Nutrition, 1887. 



