ENERGY 501 



TABLE 21-2. Caloric Values and Compositions of Some Human Foods 



Composition, % 



Since the heat contents of carbohychates, fats, and proteins are 

 similar within each class and average vahies are known (page 499), 

 the simplest procedure for evaluating the heat content of a food is 

 calculation from composition data. The carbohydrate, fat, and pro- 

 tein contents of the food are determined by standard methods, and 

 the total heat content calculated from the heat contents of these three 

 classes of constituents. It is assumed that only these materials contain 

 appreciable quantities of energy. Direct calorimetry indicates that 

 this assumption seems to be generally valid. The final calculation can 

 be written in equation form. 



Heat content (kcal./g.) 



= 0^04 (% carbohydrate + % protein) + 0.09 {% fat) 



ENERGY FROM FOODS 



Practically all the energy of animals comes from their foods via the 

 metabolic reactions. In some cases the food is oxidized rather directly 

 and as completely as the pathways of metabolism allpw. In other 

 cases components of the food are stored for later use as discussed else- 



