investigators reported that early growth of young 

 pair-fed rats was consistently less when the diet 

 contained 10 or 28 percent butterfat than when 

 it contained a comparable level of corn oil. When 

 the level of butterfat was increased to 35 percent, 

 rats were as large as or larger than those on diets 

 containing 10, 28, or 35 percent corn, soybean, or 

 coconut oil. More efficient utilization of the diets 

 was observed as the level of butter was increased; 

 no such relation was noted for corn oil. Pair 

 feeding and ad libitum feeding gave similar results. 

 Hoagland and Snider (92) observed a growth- 

 promoting value of peanut oil (gain per 100 

 Calories) similar to that obtained with lard or 

 hydrogenated cottonseed oil when the level of fat 

 was 5 percent. At 30-percent levels, diets con- 

 taining lard were used more efficiently than either 

 hydrogenated cottonseed oil or peanut oil. Aaes- 

 Jorgensen and Dam (1, 2) included peanut oil in 

 many of their investigations, and in general found 

 similar growth-promoting qualities for lard and for 

 peanut oil. The increase in growth rate that 

 resulted when the fat level was increased from 7 

 to 28 percent was not due to increased caloric 

 intake. 



Body weight in reiation to age and diet in adult rats 



SP 8 HVO, SPE, SPM, SPB, and SPPB 

 diets. — Differences were observed in the rate at 

 which adult rats gained weight and in the maxi- 

 mum weight eventually attained, even when diets 

 produced a similar growth response in young 

 animals. In table 9 are summarized data showing 

 the influence of diet on body weight at different 

 ages. Included also for ready reference are the 

 more extensive data already considered for SP 8 

 HVO and SPE diets. Adult rats fed the diets 

 containing milk, beef, or peanut butter continued 

 to gain throughout their healthy lifespan and were 

 consistently heavier than rats of similar age fed 

 the semipurified diet. They also tended to become 

 heavier than rats fed the SPE diet. The older 

 surviving rats fed SPM or SPPB diet tended to 

 be larger than those of comparable age fed SPB 

 diet. Differences in caloric intake did not account 

 for some of the weight differences observed. For 

 example, between 500 and 600 days of age the rats 

 fed SPM diet gained, on the average, 70 grams, 

 whereas those fed SPB diet gained 22 grams. 

 The intakes for rats fed these two diets were 

 similar — 9,370 and 9,340 Calories respectively. 

 Additional data on the caloric intakes of these 

 rats at different ages are included in appendix 

 table 80. 



Kind and level of fat. — Differences in the 

 weights of rats fed diets containing HVO, lard, 

 or butter seemed to be attributable chiefly to 

 differences in caloric intake except for rats fed 16 

 percent lard. At 300 days of age on a similar 

 caloric intake, the average weight of rats fed 

 semipurified diet was 60 grams less than that for 

 the corresponding littermates fed SP 16 lard. 



Level of protein and fat. — -The caloric con- 

 sumption of rats fed SPa 16 HVO and SPb 8 HVO 

 was approximately 5 percent more than that of 

 rats fed the semipurified diet, and accounted for 

 the tendency to larger animals on these two diets. 



Egg and egg components. — No appreciable 

 change in the weight curve of adult rats resulted 

 from replacing 30 percent of the protein of SPa 16 

 HVO diet with egg white (SPEW). When egg 

 yolk supplied all of the fat in the diet (SPEY), 

 weight changes for the adult, like those for the 

 young rat, resembled those observed with SPE 

 diet. Rats fed 100 percent egg (E100) remained 

 relatively small but did eventually reach Aveights 

 similar to those of stock rats. On SPW diet, rats 

 tended to be small throughout life although the 

 weight of the older rats was somewhat greater than 

 that of the rats fed E100 diet. On 1 00 percent 

 egg yolk, food consumption increased with age, 

 so that weights of rats surviving 400 days were 

 comparable to those of SP S HVO rats. 



Wistar rats fed SP S HVO and SPE diets. — 

 Wistar rats fed SP 8 HVO and SPE diets showed 

 a somewhat different age-weight relationship than 

 did BHE rats. On the semipurified diet, Wistar 

 rats were consistently smaller than BHE rats of 

 comparable age; on SPE diet, Wistar rats even- 

 tually became much heavier. 



Discussion. — Reports in the literature on diet 

 in relation to weight throughout the life of the 

 adult rat are limited and, as with the growing rat, 

 deal chiefly with the level or kind of dietary fat. 

 No reports have been located dealing with protein- 

 fat-containing foods such as have been included in 

 this publication. In general, the results obtained 

 in this laboratory and elsewhere provide consider- 

 able evidence that differences in weight gain are 

 not necessarily associated with differences in 

 caloric intake. 



With mature rats 205 to 212 days old, Forbes, 

 Swift, Elliott, and James (66) and Forbes, Swift, 

 Thacker, and others (68) observed that the energy 

 expense of utilization of isocaloric diets decreased 

 as the level of dietary fat (chiefly lard) increased 

 from 2 to 30 percent. A reduction in heat from 

 the catabolism of carbohydrates and from fat 

 synthesis was responsible for the resulting economy 

 of utilization of food energy as the level of fat 

 increased. French, Ingram, Uram, and others 

 (6.9) reported that by the time rats were 2S weeks 

 old on a diet in which 20 percent of the stock diet 

 was replaced with corn oil, their weight exceeded 

 significantly that of animals fed a diet in which 

 20 percent of the stock diet was replaced with 

 sucrose. Lundback and Stevenson (119) obtained 

 a gain of 0.6 gram per day for adult rats fed a 

 diet containing 60 percent fat chiefly as lard, in 

 contrast to no weight gain for rats on a comparable 

 caloric intake of a diet containing 71 percent 

 sucrose. 



13 



