852 XIV. NUTRITIONAL VALUE OF FATS 



female rats received 4.8% and 5.7% less total calories in the former case. 

 The increased efficiency of utilization of the high-fat diet was correlated 

 with the decreased life span, but there was no histopathologic evidence 

 that fat induced premature death. On the other hand, when one con- 

 siders the survival time of animals which are fasted following the feeding 

 of single foodstuffs, the results are quite different. Under such conditions 

 fat exhibits a superior response, as compared with that of protein and car- 

 bohydrate,^^ when the procedures of Samuels and collaborators^^ mentioned 

 in the last section were used as the basis of assessment. Roberts and 

 Samuels^^ have likewise demonstrated that the period of survival of rats 

 previously subjected to evisceration (removal of a section of the intestine 

 and of the liver) was considerably prolonged when the animals had pre- 

 viously received an exclusive fat diet beyond that when their previous 

 food intake had consisted either of protein or of carbohydrate. Thus, on 

 an average, the eviscerated animals which had received the high-fat 

 diets survived approximately seventeen hours as compared with the 

 figure of under ten hours for those on the high -carbohydrate diet.^^ As a 

 probable explanation for the superior behavior of fat in prolonging survival 

 under these several conditions, it is possible that the metabolic pattern 

 changes in the animals during the time when they have received the high- 

 fat diet. The original study of the relationship of diet to insulin tolerance 

 was carried out by Abderhalden and Wertheimer.*^ Roberts and Sam- 

 uels^^ reported that rats which had been accustomed to a high-fat diet 

 had a markedly lower susceptibility to insulin injection than did animals 

 which were on a high-carbohydrate ration. This resistance to insulin on 

 the part of the fat-fed rats was ascribed to a prolonged retention of liver 

 glycogen in these animals. Roberts et alJ^ suggested that the rats in 

 whose case 85% of the calories had been derived from fat developed a 

 sparing action for liver glycogen. Thus it was found that rats which had 

 previously received a fat regimen were free from hypoglycemic symptoms 

 and survived for a longer period during subsequent fasting than did rats 

 which had received the high carbohydrate diet.*' This phenomenon 

 has been termed "preferential utilization. "*2, 46 'pj^g characteristic metab- 



" S. Roberts and L. T. Samuels, Am. J. Physiol, InS, 57-62 (1949). 



^2 S. Roberts and L. T. Samuels, Bull. Univ. Minnesota Med. Foundation, 4, 55-59, 67 

 (1944); Am. J. Physiol., H6, 358-365 (1946). 



^3 S. Roberts, L. T. Samuels, and R. M. Reinecke, Am. J. Physiol, HO, 639-644 

 (1944). 



** E. Abderhalden and E. Wertheimer, Pfltiger's Arch. yes. Physiol, 205, 547-558 

 559-570 (1924). 



« S. Roberts and L. T. Samuels, Proc. Soc. Exptl Biol Med., 53, 207-208 (1943). 



« S. Roberts and L. T. Samuels, /. Biol Chem., 151, 267-271 (1943). 



