CH. XXXIX.] 



VARIOUS DIETS. 



589 



Exchange of Material with various Diets. 



The reasons why a mixed diet is necessary have been already explained 

 (Chap. XXVIII). Numerous experiments have, however, been made in the 

 study of metabolism on abnormal diets. 



Feeding with meat. As the chief solid in meat is proteid, one must take 

 either too much nitrogen or too little carbon. The principle that underlies 

 Banting's method of treating obesity is to give meat almost exclusively : the 

 individual then derives the additional supply of carbon necessary for com- 

 bustion from his own adipose tissue. We have already seen that this may 

 be and often is counteracted by the laying on of fat which comes from the 

 non-nitrogenous moiety of the proteid. 



Feeding with fat. If an animal receives fat only, the nitrogenous excreta 

 are derived from the disintegration of tissue without any corresponding 

 supply of nitrogen being supplied in exchange in the food. When fat only 

 is given, or a large excess of fat exists in the food, the respiratory quotient 

 falls. F. Hofmann fed a dog on a mixture of a large amount of fat and a 

 small amount of proteid. After death tha quantity of fat found in the body 

 was such that only a small part could have been derived from the proteid, 

 the greater amount being directly derived from the fat of the food. The 

 animal, moreover, lays on fat in which palmitin, stearin, and olein are 

 mixed in a definite proportion ; this proportion is often different in the fat 

 of the food. In addition to this an animal will fatten (laying on fat with 

 it> usual composition) on fatty food, such as spermaceti, which contains no 

 glycerides. 



Feeding with carbohydrates. The respiratory quotient approaches unity 

 when carbohydrates alone are taken. So far as regards nitrogen the animal 

 is in a state of inanition, as when fat alone is taken. If given in combina- 

 tion with other foods, both carbohydrates and fat act as proteid-sparing 

 foods. 



The following table is from Pettenkofer and Voit, and illustrates what 

 happens in a dog on a mixed diet of flesh and carbohydrates. 



Even when the diet consists wholly of carbohydrates, fat is laid on : the 

 fat laid mi when meat and starch are both present in the food comes partly 

 from the proteid and partly from the carbohydrate of the food. When no 

 carbohydrate is given at all, as in the last experiment, the nitrogenous 



