SOURCE OF THE BODY FAT 



441 



The Energy Value of Fats in Metabolism. Fats, in comparison 

 with other food principles, are of especial value as sources of energy. They 

 are completely oxidized in the body to carbon dioxide and water, and yield, 

 therefore, as much energy to the body as they yield upon oxidation outside 

 the body. The energy equivalent of i gram of fat is 9 . 3 large calories, 

 more than twice that of starch or of protein, which in the body yield only 

 4 . i calories each per gram. 



A study of the elimination of nitrogen and of carbon during fasting shows 

 that the fats contribute to energy formation for many days. This is illus- 

 trated by the following computation by Voit: 



METABOLISM IN A DOG DURING FASTING. (VoiT.) 



The amount of fat metabolized is sharply influenced by the amount and kind 

 of other food. For example, if the amount of fat metabolized per day in 

 fasting is first determined, then a ration of protein given for a few days, 

 followed by a second fasting period, it will be found that the metabolism of 

 body fat is sharply increased in the second period, due to the stimulating 

 influence of the protein. 



This is demonstrated by the following determination of Rubner: 



The fat of the ordinary daily diet is absorbed into the blood and no doubt 

 contributes directly to oxidation processes. Just the steps in this oxidation 

 process cannot at present be given. If the fat food is insufficient, then the 

 body store is drawn upon; if in excess, then it is stored in the body. 



Source of the Body Fat. Excess of fat in the food can be stored as 

 fat in the body. This fact is demonstrated by Voit, Hoffmann, Rubner, 



