METABOLISM 195 



Conversion oj Carbohydrates into Fats 



The carbohydrate metaboHsm thus far discussed may be 

 considered as the most direct metaboHc change which carbo- 

 hydrates undergo, in order to yield their energy to the animal 

 body. In these changes the carbohydrate remains always as 

 carbohydrate, simply passing from mono- to poly-saccharoses, 

 and vice versa, until it is finally oxidized. Another metabolism 

 of carbohydrates occurs, however, in which they become con- 

 verted into compounds that are not carbohydrates. This is 

 the metabolic conversion of carbohydrates into fats. 



The fact that the feeding of carbohydrate food increases the 

 fat of animals has long been known and is the basis of practical 

 animal feeding. The farmer feeds, not fat food, but largely 

 carbohydrate food, e.g. grain, in order to increase body fat or 

 to maintain a large production of milk fat. We cannot follow 

 in detail the reactions by which carbohydrate food is converted 

 into fat, but we can simply state the fact that such conversion 

 does take place in the animal body. It is probably true that 

 fat is not formed from carbohydrates until both liver glycogen 

 and muscle glycogen have been stored to their maximum 

 amounts ; that is, until all temporary reserve supplies for energy 

 demands are filled. When such a condition occurs and the 

 supply of carbohydrate food is still in excess, then this excess 

 carbohydrate becomes converted into fat. 



Feeding Experiments. — While this conversion is a fact, as 

 shown by common feeding practice, it has likewise been estab- 

 lished by direct experiment. By feeding pigs and milch cows 

 with rations carefully analyzed and calculated for the exact 

 amounts of carbohydrate, fat and protein eaten and digested ; 

 and then, similarly, accurately determining the gain in fat, in 

 the case of the pigs, and the amount of milk fat produced in 

 the case of the milch cows, it has been proven in both cases 

 that the fat produced was very largely in excess of that possible 

 of formation from the fat and protein of the food and must, 

 therefore, have been formed from the carbohydrate. 



