NUTRITION 113 



agreed, however, that the nutritive value of the amides of the 

 food is much lower than that of the true protein. 



It has been shown (p. in) that the protein of animal 

 bodies cannot be formed from the non-nitrogenous matter 

 (fats and carbohydrates) of the food. The converse, however, 

 is not true. Under certain conditions, body fat may be formed 

 from the protein of the food. A certain amount of protein 

 is required to repair the waste due to oxidation. If there be 

 any excess in the food, a small proportion of it can be stored 

 up as tissue, and fat may be formed from the remainder. 



It was at one time thought that all the body fat was 

 normally formed in this way. It is now known that, under 

 ordinary circumstances, it is mainly formed from the fat and 

 carbohydrates of the food. The process appears to be quite 

 independent of the protein. It may take place not only when 

 there is an insufficiency, but even in the total absence of protein 

 in the food. In other words, an animal body may gain fat and 

 lose protein (not relatively, but absolutely) at the same time. 



The fats do not suffer disintegration to the same extent as 

 the proteins in the process of digestion. At most they are 

 resolved into glycerine and fatty acids, and are re-formed by 

 combination of these ingredients after absorption. No doubt, 

 owing to partial or complete oxidation of some of the acids 

 and readjustment of the radicles, the re-formed products differ 

 considerably from the original fat of the foods ; but they often 

 retain something of their character. Beef made from cattle 

 that have been fed largely on cod liver oil sometimes has a 

 faintly fishy taste. The melting point and other characteristic 

 properties of butter fat are very directly influenced by the 

 amount and character of the fat in the food. 



Numerous experiments show that body fat may also be 

 formed from the carbohydrates of the food. All these com- 

 pounds are easily converted into sugars, and to a large extent 

 they are so converted in the process of digestion. Probably 

 all the body fat formed from carbohydrates passes through 

 the stage of sugar. It must not be forgotten, however, that 

 the methane of the intestinal gases is also derived from the 

 carbohydrates. 



