FATS AS ESSENTIAL DIETARY COMPOXEXTS 857 



drcd revohiTions of work A\as found to be lowest in the fat group; thus the 

 figures are 0.0521 for the protein group, 0.0465 for the cari^ohydrate group 

 and, finally, 0.03-12 for the group which had previously rec'ei\'ed the high- 

 fat diet. 



It was demonstrated l)y French, Black and Swift'-- that a more efficient 

 energy utiUzation with an increase in weight, and decreased heat produc- 

 tion, obtained in rats on a low-protein diet when 30% of fat was present 

 than when only 2% of this foodstuff was availai^le. Obviously the high- 

 fat level enabled the protein to be better utihzed. Geiger" and Salmon^* 

 likewise observed that the sparing effect of cystine on the utilization of 

 casein is exerted onl}' when fat is present in the diet. Rogers and co- 

 workers"^ demonstrated another situation in which fat has an especially 

 beneficial effect upon the retention of proteins as compared with other 

 foodstuffs. Thus, the rate of liver regeneration, after a 70% partial 

 hepatectomy was carried out in the case of rats previously depleted of 

 protein, was found to be better when the animals were given a 30% fat 

 diet than when they received a 3% fat regimen ad libitum. It would 

 therefore appear that the inclusion of fats in the diet has a beneficial effect 

 upon protein metabolism. Further data on the mechanism of action of 

 fat in sparing protein are gi\'en in the review bj- ^Nlunro.^" 



(8) The Effect of Dietary Fat in Stress Conditions 



The foregoing discussion has been concerned largely vrith the role of 

 fats in general in helping the animal meet physiologic forms of stress, such 

 as gro^Ai/h, pregnancy and lactation, work, maintenance of protein stores, 

 and similar demands. It is also of considerable importance whether or 

 not fat may function in a specific manner when the animal is subjected to 

 exogenous forms of stress, such as thyrotoxicosis, induced by the adminis- 

 tration of thyroid, x-irradiation, cold, and hepatectomy. 



a. Thyrotoxicosis. The thyroid gland is associated with so many 

 varied functions in the animal body that any increased activity of this 

 gland may cause wide-spread changes in certain physiologic indices. The 

 stress which can be brought about by the administration of the thjToid 

 hormone is similar to that produced by the feeding of desiccated thjToid 

 powder, and also parallels the effect of hyperactivity of the gland. Among 



'" E. Geiger, Personal pommunication, 1952. 

 5s W. D. Salmon, ./. Nutrition, SS, 155-168 (1947). 



" C. S. Rogers, (\ C. Ferguson, C. E. Friedgood, and H. M. Vars, Am. J. Physiol., 

 les, 347-353 (1950). 



«« H. X. Munro, Physiol. Revs., SI, 449-488 (1951). 



