diets containing the same fat at the 16-percent 

 level. Eats fed the diet containing butter tended 

 to be smaller than those fed comparable levels 

 of HVO or lard. The diet containing 16 percent 

 lard was the only one used with an efficiency 

 comparable to that seen for the diets containing 

 egg, milk, beef, or peanut butter. The range 

 of values observed was wide, and more data on 

 this group of diets are needed to establish the 

 significance of these trends. 



Level of protein and fat. — When diets 

 contained 30 percent protein as casein and 

 lactalbumin (SPb 8 HVO and SPa 16 HVO), 

 growth rate and calorie-per-gram gain were similar 

 to the results obtained for comparable levels of 

 fat when the diet contained 25 percent protein 

 (SP 8 HVO and SP 16 HVO). 



Egg and egg components. — Rats fed a diet 

 (SPEW) in which egg white replaced 30 percent of 

 the protein in SPa 16 HVO diet tended to be 

 smaller. Growth response and utilization of diets 

 in which egg yolk replaced approximately 50 per- 

 cent of the protein and approximately 80 percent 

 of the fat in SP 16 HVO were similar to the results 

 for rats on SPE diet. Rats fed a diet (SPW) in 

 which egg white replaced all of the casein and 

 lactalbumin in the semipurified diet were small. 

 No data were obtained on the calories-per-gram 

 gain for this diet. Evaluation of growth on and 

 utilization of diets of 100 percent whole egg or 

 egg yolk was complicated by the tendency to 

 frequent diarrhea in the rats fed these diets. 

 Food consumption and caloric intake of these two 

 high-fat diets were low, and rate of growth was 

 correspondingly reduced. 



WlSTAR RATS FED SP 8 HVO AND SPE DIETS. 



Wistar rats fed SP 8 HVO and SPE diets ate less 

 and grew at a slower rate than did BHE rats fed 

 comparable diets. Wistar rats seemed to use 

 both diets more efficiently for growth than did 

 comparable BHE rats, but the differences ob- 

 served may be due in whole or in part to the 

 smaller weight that was being maintained by the 

 Wistar rats during this period of rapid growth. 

 However, both Wistar and BHE rats tended to 

 grow more rapidly and to use their food more 

 efficiently when fed SPE diet than when fed SP 

 8 HVO diet. 



Discussion. — Although the levels of fat in the 

 diets investigated were not considered excessive, 

 there appeared to be a consistent trend for rats to 

 become larger at an earlier age when the fat level 

 was 17 to 19 percent than when it was 9 percent 

 or less. In some instances, the increased growth 

 rate appeared to be explained by differences in 

 intake alone; in others, a decrease in calories-per- 

 gram gain — that is, more efficient utilization of 

 the diet — accompanied the increased growth rate 

 observed. 



Deuel (48) in reviewing the subject of dietary 

 fat and growth, concluded that the preponderance 

 of evidence favors the hypothesis that in the rat 

 greater increases in weight and unproved effi- 



ciencies of the diet are associated with increased 

 consumption of fat. In studying the associative 

 dynamic effects of protein, carbohydrate, and fat, 

 Forbes and Swift (64) showed that fat is particu- 

 larly effective in reducing the specific dynamic 

 effects of diets. 



Reports in the literature on the response of the 

 rat to fat have dealt chiefly with the influence of 

 different kinds and levels of fat rather than with 

 fat-containing foods such as egg, milk, beef, or 

 peanut butter. Lard has been most frequently 

 used in investigations dealing with the response to 

 dietary fat. In weanling rats fed for a period of 

 from 8 to 10 weeks, there has been a tendency for 

 weight gain to correlate with the level of this fat. 

 The differences reported have usually been small 

 and in some investigations have not proved 

 statistically significant. 



Hoagland and Snider (93) found weight gains 

 per 100 Calories to be approximately the same for 

 diets containing 15, 30, or 54 percent lard, but at 

 these levels the gains were significantly greater 

 than those observed with 5 percent of this fat. 

 Hoagland, Snider, and Swift (94) found that the 

 differences were not significant when isocaloric 

 amounts of diets containing 5, 10.98, or 18.27 per- 

 cent lard were fed. Forbes, Swift, Elliot, and 

 James (65) reported weight gains to correlate with 

 level of fat when rats were fed isocaloric quantities 

 of diets containing 2, 5, 10, or 30 percent fat. 

 Two percent corn oil was present in all of the 

 diets, and the additional fat was lard. The 

 largest difference observed was that between the 

 diets containing 2 percent fat and those containing 

 5 percent fat. Forbes, Swift, James, and others 

 (67) reported a similar experiment using large 

 increases in the intake of 10 of the vitamins, and 

 again demonstrated that fat confers efficiency of 

 utilization of food energy for the growing albino 

 rat; however, the small increments in weight gain 

 observed as the level of fat increased from 2 to 

 30 percent were not statistically significant. 



Hoagland and Snider (93) compared the relative 

 efficiency of lard and hydrogenated cottonseed oil 

 as dietary fats. At all except the lowest level 

 tested (5 percent), lard proved significantly more 

 efficient in promoting growth than did hydroge- 

 nated cottonseed oil. The diet containing 15 per- 

 cent hydrogenated cottonseed oil appeared some- 

 what more efficient than the diet containing 5 per- 

 cent of this fat; at still higher levels the response 

 was similar to that observed with diets containing 

 15 percent fat. Marshall, Hildebrand, Dupont, 

 and Womack (126) fed ad libitum diets containing 

 15 percent hydrogenated vegetable oil or lard. 

 Weight gain per 100 Calories during the period of 

 rapid growth was slightly more on the diet con- 

 taining lard, but the differences were small and 

 not statistically significant. 



According to Barki, Collins, Elvehjem, and Hart 

 (17), conclusions with regard to the growth-pro- 

 moting properties of fats may be misleading if 

 comparisons are confined to one level of fat. These 



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