By NICHOLAS WADE, New York Times

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.

Would the same be true in people? More than 20 years ago, two studies of rhesus monkeys were begun to see if primates responded to caloric restriction the same way that rodents did. Since rhesus monkeys live an average of 27 years and a maximum of 40, these are experiments that require patience.

The results from one of the two studies, conducted by a team led by Ricki J. Colman and Richard Weindruch at the University of Wisconsin, were reported Thursday in Science. The researchers say that now, 20 years after the experiment began, the monkeys are showing many beneficial signs of caloric resistance, including significantly less diabetes, cancer, and heart and brain disease. “These data demonstrate that caloric restriction slows aging in a primate species,” they conclude.

Some critics say this conclusion is premature. But in an interview, Dr. Weindruch called it “very good news.”

“It says much of the biology of caloric restriction is translatable into primates,” he said, “which makes it more likely it would apply to humans.”

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