FOODS. 



127 



Mixed Diet. The chemic composition of the tissues, taken in con- 

 nection with their metabolism during starvation, implies that no one article 

 of food is sufficient for tissue repair and heat production; but that all classes 

 of foods in other words, a mixed diet are essential to the maintenance of 

 a normal nutrition. Experimental investigation has also conclusively 

 established this fact. Moreover, the amounts of nitrogen and carbon elimi- 

 nated daily, and the ratio existing between them, indicate the amounts 

 of protein, fat, and carbohydrate which are required to cover the loss. 



Metabolism on a Purely Protein Diet. Notwithstanding the chemic 

 composition of the proteins and the possibility of their giving rise to either 

 fat or a carbohydrate during their metabolism it has been found extremely 

 difficult to maintain the normal nutrition for any length of time on a pure 

 protein or fat-free flesh diet. This, however, has been accomplished with 

 dogs. It was found, however, that, in order to maintain the equilibrium, 

 it was necessary to increase the proteins from two to three times the usual 

 amount. Thus, a dog weighing 30 to 35 kilograms required from 1500 to 

 1800 grams of flesh daily in order to get the requisite amount of carbon to 

 prevent consumption of its own adipose tissue. Under similar circumtances, 

 a human being weighing 70 kilograms would require more than 2000 grams 

 of lean beef an amount which, from the nature of the digestive apparatus, 

 it would be practically impossible to digest and assimilate for any length 

 of time. Even the slight habitual excess beyond the amount normally 

 required is imperfectly assimilated and gives rise to the production of 

 nitrogen-holding compounds which, on account of the difficulty with which 

 they are eliminated by the kidneys, accumulate within the body and develop 

 the gouty diathesis, with all its protean manifestations. 



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. 



