FOODS 131 



Metabolism on a Fat and Carbohydrate Diet. As nitrogen is an 

 indispensable constituent of the tissues, it is evident that neither fat nor 

 carbohydrates can maintain nutritive equilibrium except for very short 

 periods. On such a diet the tissues consume their own proteins, as shown by 

 the continuous excretion of urea, though the amount is less than during 

 starvation. An excess of fat retards the metabolism of proteins. The same 

 holds true for the carbohydrates. 



Thus, in any well-arranged dietary there should be a combination 

 of proteins, fats, and carbohydrates in amounts sufficient to maintain nutritive 

 equilibrium; in other words, to repair the loss of tissue and to furnish the 

 requisite amount of energy in accordance with work done, as well as with 

 climatic and seasonal variations. 



COMPOSITION OF FOODS 



The food principles essential to the maintenance of the nutrition of 

 the body are contained in varying proportions in compound substances 

 termed foods; e.g., meat, milk, wheat, potatoes, etc. Their nutritive value 

 depends partly on the amounts of their contained food principles and 

 partly on their digestibility. The dietary of civilized man embraces foods 

 derived from both the animal and vegetable worlds. 



The following tables show the percentage composition of the edible 

 portions of foods as well as the amount of heat liberated per pound when 

 oxidized in the body, according to Atwater and Bryant. 



Composition of Animal Foods. The following table shows the average 

 percentage composition of various kinds of meats, cow's milk, and eggs: 



Meats. It will be observed from these analyses that the meats contain 

 from 18 to 20 per cent, of protein material. The proteins are two in number 



