A long-awaited study of aging in rhesus monkeys suggests, with some reservations, that people could in principle fend off the usual diseases of old age and considerably extend their life span by following a special diet.

Known as caloric restriction, the diet has all the normal healthy ingredients but contains 30 percent fewer calories than usual. Mice kept on such a diet from birth have long been known to live up to 40 percent longer than comparison mice fed normally.

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