CHAPTER XVI 

 FAT METABOLISM. OBESITY 



HAVING discussed the manner in which the food fat is 

 taken up from the intestine, how it enters the blood and is 

 distributed with the latter in the body, we may next endeavor 

 to gain some insight into the methods by which, having 

 accumulated in the economy, it is transformed in metabolism, 



We should start with the fact that fat serves as an 

 important source of energy and is a substance well suited 

 to limit the demand upon other materials. In contrast to 

 protein it is strikingly distinguished by its capacity for being 

 stored as a reserve substance in times of abundant supply ; 

 while, as is well known, we are not directly in position to in- 

 sure a new formation of organized body-protein by an 

 abundant proteid food supply. 



Dependence of Protein Destruction Upon Supply of Fat. 

 When protein and fat are ingested at the same time the 

 amount of protein required can be kept down by the latter. 

 While (following the teachings of the Voit school) in a dog 

 fed on proteid material alone the nitrogen balance can be 

 maintained only by supplying three and one-half times the 

 amount of protein exchanged in inanition, the nitrogen 

 balance may be successfully maintained, if fat be also ex- 

 hibited, with but one and a half or two times the amount of 

 protein metabolized in starvation. At first glance the state- 

 ment based on Voit's authority that in a starving dog, whose 

 fat deposits have not as yet been consumed, administration 

 of several hundred grams of fat scarcely influences the 

 protein exchange at all, seems surprising. The explanation 

 of this rather remarkable peculiarity is simply that in star- 

 vation fat is in demand also ; as already stated, the starving 

 body draws mainly upon fat to supply its requirements for 

 production of energy. If, therefore, a starving organism, 

 which still has a supply of fat, be flooded with fat, this added 

 fat will be surely burned in place of the tissue fat, but will 



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