304 



FAT AS A SOURCE OF ENERGY 



on a diet containing 4-52 grm. N, less than one-third of that in an 

 average man's diet. Many physiologists, especially Chauveau and 

 his school, have supposed that isodynamic amounts of fat and carbo- 

 hydrate (amounts which the same number of Calories when burnt 

 with 2 in a bomb calorimeter) are not of equal worth as a source 

 of muscular energy. They teach that sugar is the sole source of 

 this energy, and that fat must be converted into sugar before it can 

 be utilised. In the bomb calorimeter 1 grm. fat is isodynamic with 

 2*26 grm. dextrose ; but after conversion into sugar it is only equal 

 to 1'6 grm. In place of 9*5 Cal. it equals after conversion 6*07 Cal. 



Now we have no means of determining what part of the energy 

 of the body comes from proteid, fat, or carbohydrate in the body. 

 There is no proof that the body makes any distinction between 

 these food-stuffs. The whole supply of energy is used as a whole 

 for the bodily needs. In any given experiment we can determine 

 the amount of proteid, fat, and carbohydrate metabolised, and 

 the amount of work done, but we cannot tell what part of each 

 of these stuffs is metabolised in performance of the work. 



Atwater has settled the question by placing a man in his 

 respiration calorimeter on a diet not quite sufficient for mainten- 

 ance, so that the food-stuffs were used with the greatest economy. 

 The same amount of easily digestible proteid was given each day, 

 the same amount of external work done, and as the conditions 

 of life and temperature were uniform, the same amount of energy 

 was produced. Fat was fed in addition to the proteid in one case 

 and carbohydrate in the other. In each case the same isodynamic 

 value of the food-stuff was given. If under these conditions the 

 loss of body substance is greater in one case than in the other, 

 then it is clear that one food-stuff has a lower value than the 

 other, as a source of muscular energy. 



The following is the average of four experiments on an athletic 

 student, lasting fifteen days altogether : 



