IS LATE-LIFE CALORIC RESTRICTION BENEFICIAL

Caloric restriction initiated in young mice and rats results in increa ses in mean and median life span. When caloric restriction is implemen ted in older animals, an increase in life span is still observed; howe ver, the magnitude of the increase is not as great as that observed in animals calorie restricted since they were young. Here we report the results of a pilot study in which caloric restriction was initiated in mature, older rats. Survival rates and terminal pathology were charac terized and compared between a cohort of 17 continually ad libitum fed Long Evans rats and a cohort of 18 Long Evans rats, which were gradua lly introduced to 33% restriction in diet consumption at 18 months of age. No difference in the median life span was observed between the tw o groups. The data suggest there may be a level of maturity, or a stag e in the aging process, after which caloric restriction no longer incr eases longevity.