340 



LECTURE XV. 



These experiments show somewhat higher values for the carbohydrates 

 than for the fats. It is questionable whether this is always true, for 

 Atwater also published the results of some experiments in which this was 

 not the case. That, as a matter of fact, the fats are to be considered as 

 direct sources of muscular work, without requiring any preliminary con- 

 version into carbohydrates, seems apparent; for if we assume that the fats 

 are first transformed into carbohydrates, there will be a loss of energy 

 during their oxidation. In such a transformation, 36 per cent of the 

 potential energy of the fat would become free energy. Now 1 gram of 

 animal fat produces 9.50 calories, and 1 gram of cane-sugar 3.96 calories. 

 By the combustion, in the bomb calorimeter, 10.53 grams of fat and 

 25 . 25 grams sugar are required to produce 100 calories. The same number 

 of calories would, of course, be liberated in the body during complete com- 

 bustion. If the carbohydrates alone were the source of muscular energy, 

 36 of the 100 calories from the 10.53 grams of fat would not be utilized. 

 These would be set free in the body during the transformation of the fats 

 into carbohydrates and appear as heat. The ratio of the 10.53 grams 

 fat to the 25.25 grams carbohydrate would be 64 : 100. This, as a 

 matter of fact, is not the case, as the following table shows. In it the 

 relative values of a carbohydrate and of a fat diet, as shown by the above 

 experiments, are compared; in one case the amount of energy transformed 

 per day is given in calories, and in the other the percentage of utilization 

 of the fat diet is compared with that of the carbohydrate diet, and fat 

 alone is compared with carbohydrate. 



PERCENTAGE UTILIZATION OF ENERGY. 



Instead of the theoretical ratio of 64 : 100 we find that the fat stands 

 to the carbohydrate in the proportion of 95.5 : 98.0. Thus, it is evident, 

 unless we choose a far more complicated explanation, that the energy 

 which the body receives in the form of fat is a direct source of muscular 

 energy, and that a preliminary transformation of fat into carbohydrate 

 does not take place. 



