Compare two cage-by-cage photos of the monkeys and the difference is obvious: A 29-year-old monkey happens to be the oldest non-dieting monkey still alive, and a 27-year-old the oldest still-living dieter. Yet the dieting monkey looks many more years younger than his fatter, frumpier neighbor, not just a mere two.

"All these pieces put together provide rather convincing evidence in our view that caloric restriction can slow the aging process in a primate species," said lead researcher Dr. Richard Weindruch, a University of Wisconsin-Madison professor heading the NIA-funded study.

He contends that somehow the diet change is reprogramming metabolism in a way that slows aging.

The federal government is funding a small study to see if some healthy normal-weight people could sustain a 25 percent calorie cut for two years and if doing so signals some changes that might, over a long enough time, reduce age-related disease.

But NIA's Finkelstein cautions that people shouldn't just try this on their own; cutting out the wrong nutrients could cause more harm than good. Just follow commonsense healthful lifestyle advice, he said.

"Everyone's obviously looking for the magic pill," and there's not one, Finkelstein said. "Watch what you eat, keep your mind active, exercise and don't get run over by a car."