FATS AS ESSENTIAL DIETARY COMPONENTS 849 



effect is to be traced to the essential fatty acid content of the fat is not 

 entirely clear. In this conection, it was demonstrated by Deuel, Martin, 

 and Alfin-Slater*^ that female rats are able to cast normal litters and to 

 raise their pups to weaning quite satisfactorily when they are fed a fat- 

 free diet supplemented with 40 to 80 mg. of methyl linoleate daily. It 

 would appear that the most important factor contributed by fats to preg- 

 nancy and lactation is the presence of the essential fatty acids. 



(4) The Effect of Dietary Fat upon Work Capacity 



Although carbohydrate has long been regarded as the main source of 

 energy for muscular activity, a number of recent observations point to 

 the fact that fats may pla}^ a very important role in this function. Krogh 

 and Lindhard^^ reported, many years ago, as a result of respiration ex- 

 periments on human subjects, that carbohydrate was utilized about 10% 

 more efficiently for muscular work than was fat. These results are diamet- 

 rically opposed to the verj^ exhaustive studies made by Anderson and 

 Lusk" on dogs. The latter investigators reported that the animals ran 

 with equal efficiency, from the caloric standpoint, irrespective of whether 

 they had a non-protein respiratory quotient of 1.0 (indicating oxidation 

 mainly of carbohydrate) or one of 0.71 (indicating fat oxidation), which 

 was obtained after a thirteen-day fast. The present author is inclined 

 to accept the latter experimental findings, since it is far easier to control 

 the experimental conditions in tests on dogs than it is in the case of ex- 

 periments on man. It is of course possible that the variation in results 

 obtained by these two groups of investigators may have been due to the 

 fact that the .first group employed human subjects while the second group 

 used dogs. However, there is no evidence that variations of such a nature 

 occur in the utilization of carbohydrates ^nd fats in man and in dogs. 

 More recently the total working capacity has provided a closely related 

 index for comparing the nutritional values of foodstuffs. Thus Deuel 

 and collaborators^^ employed a swimming test which has been devised 

 by Scheer and co-workers^^ as a method for testing the maximum work 

 capacity possible from different animals. It was demonstrated that the 

 maximum period of swimming of the rats was considerably prolonged as 

 the proportion of fat in the diet was increased. This was not to be traced 

 to variations in buoyancy of the animals, since all test animals were re- 



'« A. Krogh and J. Lindhard, Biochem. ./., 1.'^ 2n0-.36.3 (1920). 

 " R. J. Anderson and G. Liisk, ./. Biol. Chem., S2, 421-4.30 (li)17). 

 « B. T. Scheer, S. Dorst, J. F. Codie, and JJ. Soule, An. ./. Phi/HioL, l/,9, 194-203 

 (1947). 



