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A significant correlation exists between average daily food consumption and 2-yr survival in control ad libitum (AL)-fed Sprague-Dawley (SD) rats. SD rats were fed Punna Rodent Chow 5002 or a modified chow, 5002-9, with lower protein, fat, metabolizable energy and increased fiber AL or by dietary restriction (DR) to 65% of the AL amount by measurement or time (6.5 hr). At 52 wk, food consumption and key pathology biomarkers correlated with 106-wk survival. The modified chow, 5002-9 fed AL, did not significantly improve survival. SD rats fed either diet A,L consumed the greatest amount of feed and kcallrat but consumed the same amount of feed per gram body weight as DR-fed rats. At 52 wk, AL rats fed either diet had the same brain weights as D R rats, but the AL-fed rats had greater body weight and body fat content and increased heart, lung, kidney, liver, adrenal, thyroid, and pituitary weights as well as an increased incidence and seventy of degenerative and/or proliferative lesions in these organs. This study demonstrates that overfeeding best correlates with low 2-yr survival in SD rats and that simple DR by caloric restriction modifies key pathology biomarkers in the pituitary, mammary gland, kidney, and heart of SD rats at 52 wk that are predictive of 106-wk survival.

This study was designed to compare the effects of ad libitum (AL) overfeeding and moderate dietary restriction (DR) of two different diets on Sprague-Dawley (SD) rat 2-yr survival and the development of spontaneous neoplasms. SD rats were fed Purina Rodent Chow 5002 or a modified Rodent Chow 5002-9 containing lower protein, fat, metabolizable energy and increased fiber by AL or by DR at 65% of the AL amount by measurement or time (6.5 hr). At 106 wk, rats fed the 5002-9 diet AL did not have significantly improved survival over rats fed the 5002 diet AL. The 5002 diet fed DR by time (6.5 hr) improved survival for males but not females. Only DR by measurement of both diets resulted in lower mortality for both sexes. The most common cause of death in rats of both sexes fed either diet AL was pituitary tumors followed by mammary gland tumors in females and renal and cardiovascular disease in males. The overall tumor incidence by 106 wk was remarkably similar between AL and DR groups. However, compared to the 5002 AL group, a decrease in the age-adjusted (Peto analysis) incidence of pituitary adenoma was observed in all other male groups. This effect was noted in the female DR by measurement groups only. For males, compared to the 5002 AL group, a decrease in the age-adjusted incidence of pancreatic islet carcinoma was observed in the DR by measurement groups only. In females, compared to the 5002 AL group, the only other difference in tumor incidence was the mammary gland tumors, which showed a significant decrease in the age-adjusted tumor incidence or multiplicity in the 5002-9 AL, 5002-9 DR, and 5002 DR groups. Additional analyses of mammary gland tumors showed growth time (time from initial palpation until death), tumor doubling time, and tumor volume were generally not statistically significantly different between AL and DR groups, although AL females could sustain larger tumor volumes. Compared to the 5002 AL group, there were no other significant differences in the age-adjusted incidence of any other tumor site in animals fed a modified diet or subjected to moderate DR of either diet. The conclusion from this study is that moderate DR delays death due to fatal cardiovascular or renal degenerative disease and spontaneous tumors, particularly those of the pituitary and mammary gland. However, moderate DR appears only to delay the time of onset, but not the progression, of these spontaneous tumors whether measured by age-adjusted incidence, growth time, tumor doubling time, or the time between initial detection and death.

This study compared the effects of ad libitum (AL) overfeeding and moderate dietary restriction (DR) of 2 different diets on Sprague-Dawley (SD) rat survival and spontaneous, age-related proliferative and degenerative lesions. SD rats were fed Purina Rodent Chow 5002 or a modified Rodent Chow 5002-9 containing lower protein, fat, metabolizable energy, and increased fiber by AL or by DR at 65% of the AL amount by measurement or time (6.5 hr). At 106 wk, rats fed the 5002-9 diet AL did not have significantly improved survival over rats fed the 5002 diet AL. The 5002 diet fed DR by time (6.5 hr) improved survival for males but not females. Only DR by measurement of both diets resulted in lower mortality for both sexes. By 106 wk rats fed either diet by AL had the same brain weights as DR fed rats, but AL fed rats had greater body weight, body fat content, and increased heart, lung, kidney, liver, adrenal, thyroid, and pituitary weights that correlated with an increased incidence and severity of degenerative and/or proliferative lesions in these organs. Moderate DR delayed the progression of chronic nephropathy by delaying the early development of glomerular hypertrophy that initiates the development of glomerular sclerosis and nephron loss in AL overfed rats. Moderate DR lowered the incidence, severity, and progression of cardiomyopathy and other degenerative, age-related lesions and appeared to delay the development of reproductive senescence in SD females. The conclusion from this study is that moderate DR delayed onset and progression of degenerative lesions, and death due to cardiovascular or renal disease, and thus potentially improves the bioassay to detect compound-specific chronic toxicity.Keywords [F-344]) has been declining over the past 3 decades throughout the pharmaceutical and chemical industry (4, 20, 23, 24, 26, 27, 30-32, 44, 49, 53, 56, 57). The decline in survival questions the adequacy of exposure of rats to the test article in carcinogenicity studies that result in less than 50% survival at the end of the 2-yr period (4,23,32). We have observed a significant correlation between average daily food consumption and 2-yr survival in 58 control groups of ad libitum (AL) fed SD rats (25)(26)(27). While both genetic and environmental factors are involved, rat survival can be improved by simple dietary restriction (9, 10, 25-27, 38, 39, 41, 42, 56, 57, 72, 73).In a companion paper we report that moderate dietary restriction (DR) (Figs. 1 and 2). In general, the smallest decrease in body weight gain was seen in the 5002-9 AL groups, which were approximately 92-93% of the 5002 AL groups. The largest decrease in body weight gain was in the 5002-9 DR rats that were approximately 63-68% of the 5002 AL groups. For the 5002 6.5 hr DR and 5002 DR groups, the rate of body weight gain was approximately 73-78% of those observed in the 5002 AL group. After 53 wk, mean body weights of the 5002 6.5 hr DR and the 5002 DR groups were approximately 63-73% of the 5002 AL animals, while the average weights of the 5...