DIET: SPM 



DIET: SPB 



DIET: SPPB 



GRAMS 



A' 



„A-A' 



ese rats 

 (437 days*) 

 a--a Long-lived 



rats (775 days^ 



-A 



-A' 



.A' 



.A 



A 



o — -o Obese rats 

 (456 days*) 



a--a Long-lived 



rats (737 days*) 



— 



O— O 



/ A' A - 



/ X 



p A' A ~ A 

 — / A' ~ 



/ ^ 



" ? A ' 



/ ^' 

 / / 

 / / 



1 ' 

 it 



1 1 





II 





1 O- O 



-A 



Obese rats 

 (382 days*) 



A— A 



Long-lived 



rats (682 days*) 



1 1 1 1 



150 300 450 

 DAYS 



150 300 450 

 DAYS 



^AVERAGE ACE AT DEATH 



150 300 450 600 

 DAYS 



Figure 1 .■ — Comparison of growth curves of obese rats fed SPM, SPB, and SPPB diets with those of long-lived rats 

 fed the same diets. 



survival period for rats fed lard (SP 8 lard and 

 SP 16 lard) may be due in whole or in part to 

 excessive consumption, along with the tendency 

 to more efficient utilization of these diets. 



Discussion^ — There have been extensive inves- 

 tigations on the nutritional requirements of the 

 rat, but the majority of them have dealt with the 

 period of early growth. Relatively few have 

 covered the entire lifespan. Many of the early 

 experiments concerned with longevity have dealt 

 with diets deficient in one or more nutrients, result- 

 ing in retarded growth and in premature death. 

 Although growth has been the basis for studying 

 nutritional adequacy of many diets, considerable 

 evidence has accumulated to indicate that rapid 

 growth in early life may not insure optimum 

 health throughout life. 



McCay {120) was the first to demonstrate that 

 lifespan of rats could be extended by severely 

 restricting caloric intake while maintaining 

 adequate levels of essential protein, minerals, and 

 vitamins. With much less restricted intakes (33 

 and 46 percent) and without severe retardation of 

 growth and sexual maturity, Berg and Simms (21, 

 22) showed an extension of life expectancy and a 

 delay in the onset of major diseases. Ross (166, 



28 



167), investigating the effect of uniform lifelong 

 dietary regimens on the mortality pattern of rats, 

 demonstrated the possibility of modifying life 

 expectancy not only by quantitative dietary 

 restriction but also by the ratio of the protein 

 and carbohydrate components in the diet. Riesen, 

 Herbst, Walliker, and Elvehjem (158) obtained a 

 beneficial effect on survival when the caloric 

 intake of rats fed a synthetic diet was restricted. 

 Carlson and Hoelzel (41) found that intermittent 

 fasting tended to increase the lifespan of rats 

 under conditions that did not result in drastic 

 retardation of growth. Everitt and Webb (59) 

 reported for male rats that the faster an animal 

 reached its maximum weight, the sooner it 

 deteriorated and died. Callison, Orent-Keiles, 

 and Makower (40) compared the results of feeding 

 human-type diets with rats fed a stock ration. 

 The stock diet which produced the smallest early 

 weight gains resulted in adult animals with the 

 lowest maximum weight and in the best 

 physiological condition. In contrast, the fast- 

 growing animals which attained the highest 

 maximum weights were inferior in physical 

 condition, as judged by bronchiectasis and skin 

 condition. 



