Fewer calories slows aging in monkeys, a clue for humans

Also left unanswered are questions about the psychological state of monkeys who spend most of their adult lives on a forced diet, Roberts said.

Are they happy? Are they hungry? Can they think as fast?

When UCLA evolutionary biologist Jay Phelan put mice on caloric restriction, he got the distinct impression that they didn't appreciate it.

"They bit people and were more agitated," he said. In contrast, the mice who ate a normal diet "would just sit around and let you pick them up."

It also isn't clear whether caloric restriction would extend human lives by very much, Phelan said. He has combined results from animal studies with data on men on the Japanese island of Okinawa who ate 17% fewer calories than men in Tokyo. He calculated that reducing intake by 35% would extend the human life span by just two years.

"The trade-off just isn't worth it," said Phelan, who said he personally would have a hard time giving up doughnuts.

Weindruch said he was under no illusion that the monkey findings would prompt many people to adopt caloric restriction. He has started a company to create drugs that would provide the same health benefits without the need for extreme dieting.

Physiologists agreed that instead of promoting caloric restriction, a more pressing goal is to help the two-thirds of Americans who are overweight or obese shed their extra pounds.

"That would be tremendous for the health of the nation," said David Baer, a research physiologist at the U.S. Department of Agriculture's Human Nutrition Research Center in Beltsville, Md.

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karen.kaplan@latimes.com