826 NUTRITION AND HEAT REGULATION. 



from consumption and enables us to reduce the protein material 

 in our diet. Experiments show, in fact, that carbohydrate is 

 more efficient as a sparer of protein than fat. An animal fed 

 on carbohydrates alone loses less protein from the body than when 

 kept on a fat diet containing the same amount of heat energy. 

 It would seem that the body must always have sugar to oxidize. 

 If this material is not furnished in the food it is obtained by breaking 

 down the body protein itself, as is indicated by the facts of diabetes 

 and also by the fact that even in prolonged starvation the sugar 

 contents of the blood are kept at a normal level. (4) Any excess 

 of carbohydrate, taken as food, beyond the power of the tissues 

 to store as glycogen may be synthesized to form fat. Nutritional 

 experiments, described below, leave no doubt that the fat of the 

 body may be formed from carbohydrate food. It is stated that the 

 fat of the body having this origin, so-called carbohydrate fat, is 

 of a more solid consistency than the fat derived from other sources. 



Nutritive Value of Fats. The fats of food are absorbed into 

 the lacteals chiefly as neutral fats, the so-called chyle fat. They 

 eventually reach the blood in this condition, and are afterward in 

 some way oxidized by the tissues. The final products of their 

 oxidation are the same as when burnt outside the body 

 namely, CO 2 and H 2 O and a corresponding amount of energy must 

 be liberated. Speaking generally, then, the essential nutritive 

 value of the fats is that they furnish energy to the body, and, from 

 a chemical standpoint, they must contain more available energy, 

 weight for weight, than the proteins or the carbohydrates. In a 

 well-nourished animal a large amount of fat is found normally in 

 adipose tissues, particularly in the so-called "panniculus adiposus" 

 beneath the skin, in the folds of the peritoneum, etc. Physi- 

 ologically, this body fat is to be regarded as a reserve supply of 

 nourishment. When food is eaten and absorbed in excess of the 

 actual metabolic processes of the body, the excess is stored in the 

 adipose tissue as fat, to be drawn upon in case of need as, for 

 instance, during partial or complete starvation. A starving animal, 

 after its small supply of glycogen is exhausted, lives entirely upon 

 body proteins and fats; the larger the supply of fat, the more 

 effectively will the protein tissues be protected from destruction. 

 In accordance with this fact, it has been shown that when subjected 

 to complete starvation a fat animal survives longer than a lean 

 one. Our supply of fat is called upon not only during complete 

 abstention from food, but also whenever the diet is insufficient to 

 cover the oxidations of the body, as in deficient food, sickness, etc. 



The Fate of the Fat in the Tissues. The fat absorbed as 

 food may temporarily subserve several different purposes: (1) It 



