CARBOHYDRATES AND FATS. 919 



carbohydrate is being stored as fat there is an increase in the respi- 



f-^O 



ratory quotient, that is, in the ratio t ~. 



O 2 



The Source of Body Fat in Ordinary Diets. For the pur- 

 poses of demonstration the experiments made to prove the origin 

 of body fat from carbohydrate or the fat of food have made use 

 of abnormal diets and conditions. It would be a matter of practical 

 interest to ascertain whether upon normal diets the fat of the 

 body arises more easily from the fat or from the carbohydrate of 

 the food. While the question is one to which a positive answer 

 cannot be given, it seems to be probable that the result varies with 

 conditions and the nature of the animal. Experience seems to 

 show that carnivorous animals can be fattened more easily on a 

 fat diet, herbivora on a carbohydrate diet. In animals, like our- 

 selves, there is reason to believe that the carbohydrates are more 

 easily and more quickly destroyed in the body than the fats, and 

 that, therefore, the latter may be more readily deposited in the tis- 

 sues, although an excess of carbohydrate beyond the actual needs 

 of the body will also be preserved in the form of fat or glycogen.* 



The Cause of the Deposit of Body Fat Obesity. Our 

 experience shows that individuals differ greatly in the ease with 

 which they form fat. Some upon relatively small diets form much 

 fat, while others remain thin in spite of the ingestion of large 

 amounts of food. Voit has indicated the general reason for this 

 difference namely, that it depends upon the capacity of the 

 body to destroy food material. When food is supplied and 

 absorbed in excess of this capacity the excess is stored to a small 

 extent as glycogen, but chiefly as body-fat. As stated above, this 

 holds true especially for fat and carbohydrate foods, which, speak- 

 ing generally, are the variable parts of our diet. A diet which will 

 give such an excess to one individual, may in the body of another 

 of the same weight be all consumed. The oxidizing or metab- 

 olizing capacity of the body differs in different individuals and 

 some will lay on fat more readily than others, because for them 

 an excess of material is provided by a relatively small diet. Theo- 

 retically, it is possible that in such cases the activity of the fat cells 

 may be greater than normal. One might assume a certain balance 

 between the oxidizing capacity of the tissues in general and the 

 fat-forming activity of the cells of the adipose tissue, and suppose 

 that this balance may be disturbed either by a decrease in one factor 

 or an increase in the other. The administration of thyroid tissue 

 which is known to increase the oxidations of the body leads to a' 

 loss of body fat, and this method is sometimes employed to reduce 



* Consult Rosenfeld, "Ergebnisse der Physiologie," vol. i., part I, 1902. 



Complete literature. 



