1 78 NUTRITION, DIETETICS AND ANIMAL HEAT 



however, takes place under the influence and through the agency 

 of the cells. It is scarcely necessary to add that neither fats nor 

 carbohydrates, nor both together, are sufficient to sustain life; 

 for life is embodied in protoplasm and protoplasm must have 

 nitrogen, which element these foods cannot furnish. 



Formation of Adipose Tissue. The adipose tissue in^the 

 body is not the result of direct deposition of the oleaginous foods. 

 The amount of fat taken on in a given time by some animals, as 

 hogs, is often far in excess of the quantity of fat in the ingesta. 

 Adipose tissue is, under normal conditions, the result always of 

 changes due to protoplasmic activity. It is formed by the tissues 

 chiefly from the carbohydrates, but also to a less extent from 

 the proteids. The chemical changes by which sugar is con- 

 verted into fat are as yet undetermined, but there are so many 

 evidences of an increase in body fat upon an excess of carbo- 

 hydrate food that the fact itself that this class of food is the 

 main source of fat is no longer disputed. 



As regards the formation of fat from proteids, it is thought that 

 the molecule is split up into a nitrogenous molecule, which is 

 discharged as urea, and a non-nitrogenous, which at once, or 

 after undergoing other changes, is deposited as fat. Experi- 

 mental observations demonstrate that the liver produces gly- 

 cogen on a purely proteid diet. Since glycogen is a carbohy- 

 drate, and carbohydrates are the chief source of body fat, it is not 

 improbable that the non-nitrogenous molecule of the proteid 

 dissociation takes the form of glycogen and is later converted 

 into fat after the manner, whatever it may be, of the glycogen 

 introduced in carbohydrate form. When the carbon discharged 

 is less than the carbon ingested the deficit is thought to be retained 

 to form fat, which is deposited as a reserve to be used whenever 

 its oxidation may become necessary as a supply of energy. 



It follows that to reduce body fat the carbohydrates should be 

 largely interdicted, while to increase it they should be taken in 

 excess. In human beings proper regulation of the diet is more 



