FATS AS ESSENTIAL DIETARY COMPONENTS 851 



All of the data which have been advanced in comparing work capacity 

 would appear to support the view that rats which receive a high-fat diet 

 or Avhich, previous to fasting, have received high-fat diets, use fat more 

 economically insofar as the source of calories is concerned than they do the 

 other foodstuffs. In the case of the fasting rats this would allow the ani- 

 mals to sur\'ive for a longer period of time and to carry out a larger pro- 

 portion of work than did animals which received a non-fat diet. How- 

 ever, Ershoff,'^^^ using different experimental conditions, observed that 

 the swimming performance of rats and mice at a water temperature of 

 20° C. was iiu'ersely proportional to the fat content of the diet. In this 

 later experiment, the stressor agent was not work per se but, at least in 

 part, the stress of inmiersion in cold water, and the attendant loss of body 

 temperature. 



(J) The Effect of Dietary Fat upon Survival Time during Subsequent 



Fasting 



The length of life and of survival during fasting are two nutritional 

 indices which are of importance in the evaluation of the nutritive value of 

 foodstuffs. In the case of the first index, namely longevitj'', the data are 

 somewhat controversial. Carlson and Hoelzel'"' reported that rats fed 

 on a mixed diet containing 28% of fat and 35% of protein (chiefly meat) 

 lived somewhat longer than did animals which were fed on a vegetarian 

 diet containing 8% of fat and 30% of protein (whole wheat, beans, and other 

 \Tgetable proteins) but supplying more roughage on an isocaloric basis. 

 Because of variations in the type of proteins employed and in that of the 

 other foodstuffs, it is difficult to attribute the variations in longevity in 

 the aforementioned experiments solely to the variation in the fat content. 

 French and co-workers-"* observed, in 1953, that the life span of male rats 

 ingesting a high-fat diet (22.7%) was somewhat shorter than that of the 

 animals on a high -carbohydrate diet containing only 3.4% of fat. In the 

 case of females, less pronounced differences in the span of life were noted. 

 The average ages of the group on the several diets at death were as fol- 

 lows: Males: high-fat diet, 676 ± 19 days; low-fat (high-carbohydrate) 

 diet, 765 ± 22 days; and stock diets 747 days. In the case of the females 

 the figures were as follows: high-fat diets, 752 ± 25 days; low-fat diets, 

 793 ± 24; and stock diets 794 ±31 days. The growth rate was found 

 to be identical on the high-fat and low-fat diets, although the male and 



39» B. H. Ershoff, J. Nutrition, 63, 439-449 (1954). 



« A. J. Carlson and F. Hoelzel, /. Nutrition, 34, 81-96 (1947). 



