indicates that other dietary ingredients also are 

 contributing to the response of rats to SPE diet. 



Diet keversal. — The number of rats included 

 in the series to investigate the influence of reversing 

 stock and SPE diets at 250 days of age was small, 

 and details for the individual rats are summarized 

 in table 81 of the appendix. The harmful effects 

 of the SPE diet appear to have been overcome or 

 prevented for 3 of the 4 rats that were changed 

 from SPE to stock diet at 250 days of age. The 

 4th rat was losing weight before the diet was 

 changed and died shortly thereafter. This sug- 

 gests that irreversible damage had already occurred 

 before the change in dietary regimen at 250 days. 

 The average age at death of the 3 animals that 

 were maintaining then- weight at the time of the 

 change in diet was 705 days, in contrast to a life- 

 span of 473 days for rats continuing on SPE diet 

 throughout life. Three of the 4 rats placed on 

 SPE diet after 250 days of age lived more than 700 

 days, in marked contrast to 1 out of a total of 85 

 that reached this age when SPE diet was fed 

 throughout life. These findings suggest that the 

 harmful effects of SPE diet are due to a stress 

 imposed upon the young rat, and that this diet 

 may be well tolerated by the adult rat. 



Heredity and response to SP 8 HVO or 

 SPE diet. — Wistar rats lived longer on both 

 SP 8 HVO and SPE diets than did BHE rats. 

 Over 50 percent of the rats fed these diets lived 

 more than 700 days, in marked contrast to the 

 results with BHE rats, particularly those fed 

 SPE diet. Although the average age of survival 

 of Wistar rats was somewhat less on SPE than on 

 SP 8 HVO diet, the difference was of questionable 

 significance considering that the early death of 

 two of the rats fed SPE diet was due to respiratoiy 

 infections and seemed unrelated to diet. 



The shortened lifespan that resulted from 

 feeding SPE diet to BHE rats when their parents 

 were raised on our regular stock diet also occurred 

 when their parents were raised on the stock diet 

 that had been used for the Wistar animals. 

 Genetic differences, therefore, and not differences 

 in dietary history of the parents appear to be 

 responsible for the short survival of BHE rats 

 fed SPE diet. 



Stock diet. — No systematic data were collected 

 to determine the longevity of BHE rats fed the 

 usual stock diet, but apparently these animals 

 are relatively long lived. Among the rats that 

 were sacrificed to provide information on the 

 characteristics of stock animals at different ages 

 were 10 rats over 800 days of age. Three of these 

 were still maintaining their weight and appeared 

 to be in good health at 820, 916, and 976 days of 

 age. The remaining 7 animals, from 808 to 897 

 days old, were losing weight at the time of sacri- 

 fice. Likewise, BHE rats fed the stock diet that 

 had been used for raising the Wistar rats were 

 long lived. Five rats that were continued on 

 this diet to provide data on older animals were 

 still maintaining their weight when sacrificed at 



an average age of 938 clays. No information was 

 obtained with older Wistar rats fed their usual 

 stock diet. 



Early weight gain and survival. — Although 

 the experiments reported in this bulletin were not 

 designed to determine the influence of food con- 

 sumption and/or weight on survival, they afford 

 considerable indirect evidence indicating that ex- 

 cessive food consumption and the accompanying 

 rapid gain in body weight were important factors 

 in determining the lifespan of these rats. In 

 table 13 are summarized data for gross caloric 

 intake by rats fed SP 8 HVO and SPE^diets during 

 the first 300 days of life, with the results separated 

 into groups based on the age at which consistent 

 weight loss began. The average intake on both 

 diets tended to be less, particularly during the 

 200- to 300-day period, for rats with the longer 

 span of healthy life, although there was consider- 

 able variation in the food intake of individual rats. 

 All except 1 of the 9 rats fed SP 8 HVO diet with 

 a caloric intake of 1,900 Calories or more lost 

 weight and showed signs of ill health before they 

 reached 600 days of age. Considering the simi- 

 larity in the caloric intake of rats fed SP 8 HVO 

 and SPE diets, however, it was apparent that 

 differences in the lifespan on these two diets were 

 not due to differences in the amount of food eaten 

 by these animals. 



The adverse effect of rapid weight gain in the 

 young adult rat is still more apparent from the 

 data shown in figure 6. Curves 1 and 2 contrast 

 the growth curve of a group of rapidly growing 

 rats fed SP 8 HVO diet with that of rats of rela- 

 tively long lifespan; curves 3 and 4 represent 

 similar data for rats fed SPE diet. The 14 

 rapidly growing rats fed SP 8 HVO diet all had 

 attained a body weight of 550 grams by the time 

 they reached 200 daj^s of age; 4 exceeded 600 

 grains in weight. The average age at death of 

 these rats was 553 days. Curve 2 shows the 

 slower growth rate of 14 rats that were fed the 

 same diet and survived 600 days or more without 

 weight loss. Most of the rats in this latter group 

 weighed less than 500 grams at 200 days of age, 

 and none had reached a weight of 550 grams. 

 The average age at death was 812 days. The 

 16 rapidly growing rats fed SPE diet all exceeded 

 600 grams in weight by 200 days, with an average 

 age at death of 423 days. By 600 days, most of 

 the rats fed SPE diet were dead or were losing 

 weight, regardless of early weight gain. Curve 4, 

 therefore, represents data for rats maintaining 

 or gaming weight at 500 days of age. Their 

 average lifespan of 623 days was greater than 

 that of the rapidly growing rats fed the same 

 diet, but did not equal that of rats growing at a 

 comparable rate when fed SP S HVO diet. 



Figure 7 represents similar data for a small 

 group of rats fed SPM, SPB, and SPPB diets, and 

 provides further evidence for the harmful effects 

 of early rapid gain in body weight. The curves 

 for the most rapidly growing animals fed these 



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