WORK 



121 



sparing protein between carbohydrate and fat. Both Landergren and 

 Cathcart have shown that, if a subject be put on a purely carbo- 

 hydrate diet, the output of nitrogen steadily falls during the experi- 

 ment. Unfortunately, owing to the nature of the diet, it is impossible 

 to continue it for more than five or six days at a time. If the carbo- 

 hydrate be now replaced by another diet, also nitrogen-free but con- 

 sisting solely of fat, there is an immediate rise in the output of nitrogen, 

 although the caloric intake is ample to suffice for all the body require- 

 ments. The following table very clearly shows this effect of carbo- 

 hydrate and of fat on the output of total nitrogen : 



Voit (VII) had previously demonstrated that the ingestion of fat 

 by a starving animal if anything rather increased the protein catabol- 

 ism. 



Even when protein is fed with the fat as in the experiments of 

 Voit and Korkunoff (410) the fall in protein catabolism, although it 

 reaches a level well below that for the protein alone, is not so marked 

 as in the case of protein and carbohydrate. It is impossible at present 

 to state what is the true cause of this increase in protein catabolism as 

 the result of feeding on a purely fat diet. It may be that the degree 

 of acidosis produced by the faulty combustion of fat plays a part, or it 

 may be, as Falta, Grote and Staehelin (124) have suggested, that the 

 demand for sugar is so urgent, that protein tissue is broken down to 

 obtain it. Landergren (237) has offered a very similar explanation. 

 He holds that for some unknown reason (as has been pointed out in 

 a previous section the probable reason is that carbohydrate is essential 

 for protein synthesis) carbohydrate is in constant demand by the 

 tissues. He further holds that, under physiological conditions at 

 least, fat cannot supply this want and that proteins are broken down 

 to yield the sugar which is lacking with a resultant rise in the output 

 of nitrogen. 



