838 XIV. NUTRITIONAL VALUE OF FATS 



ology and biochemistry of the essential fatty acids are reviewed in Chapter 

 XIII and also by Deuel and Reiser.^ 



2. Fats as Essential Dietary Components 



(1) The Effect of Dietary Fat upon Growth 



a. Experiments in Which ad libitum Feeding Was Employed. There is 

 considerable evidence in the literature to prove that the growth-promoting 

 properties of diets are progressively improved as the proportion of fat is 

 increased. This greater increase in body w^eight on diets containing large 

 amounts of fat may possibly be attributed merely to the fact that the 

 animals are able to consume a larger number of calories because they are 

 ingesting diets of a higher caloric density when large amounts of fat are 

 included, or because the presence of increased amounts of fat per se may 

 have some special beneficial effect on growth. Hoagland and Snider^"^ 

 proved that, when rats were fed diets containing 5, 30, or 55% of four types 

 of lard the best growth was obtained on those regimens which had 30 or 

 55% of fat. In another series of tests carried on by these same workers 

 at a later date,^^ it was found that, when steam-rendered lard and hydro- 

 genated cottonseed oil were fed at levels of 5, 15, 30, or 54% in the diet, 

 optimum growth occurred in the animals which received the 30% fat 

 diet, and the minimal growth was noted in the group receiving the lowest 

 fat level, namely 5%. Deuel and co-workers^- also reported that weanling 

 rats which were fed on several levels of cottonseed oil or margarine fat 

 grew best when the fat comprised 20 to 40% of the total weight of the diet. 

 These authors suggest that the optimum level of fat estimated from these 

 tests would be approximately 30% by weight, or 50% on the basis of 

 calories.'^ Figure 1 represents the mean body weights, at the several 

 periods, of weanling rats fed over an eighteen-week period on diets contain- 

 ing several levels of fat. According to these data the best growth was ob- 

 tained on diet 63, which contained 20% by weight of cottonseed oil or 

 margarine fat. 



(a) Experiments on Rats Maintained on Restricted Calories. The im- 

 provement in nutrition and growth which results from the inclusion of 



9 H. J. Deuel, Jr., and R. Reiser, Vitamins and Hormones, 13, 29-70 (195.5). 

 w R. Hoagland and G. G. Snider, U. S. Dept. Agr. Tech. Bull, No. 725, 1-12 (1940). 

 " R. Hoagland and G. G. Snider, J. Nutrition, 22, 65-76 (1941 ). 



12 H. J. Deuel, Jr., E. R. Meserve, E. Straub, C. Hendrick, and B. T. Scheer, J. 

 Nutrition, 33, 569-582 (1947). 



13 H. J. Deuel, Jr., J. Am. Dietet. Assoc, 26, 255-259 (1950). 



