We know already fat or lack of it has vast implications in the lives of people, but putting them on an austere diet just isn ™t feasible.

It ™s easy to put rodents on a spartan diet. With people it ™s not so easy; they don ™t want to diet," said Guarente.

In fact, the side effects in a human being whose diet was cut by about 50 percent ”down to 1,000 to 1,200 calories a day, the reduction necessary to get the 50 percent extension in the lifespan ”would create a very lean, cold, unhappy person with no sex drive. It would be like eating every other day," says Guarente.

Unless, that is, you could find a way to mimic the molecular effect of famine without the actual dieting.

If we could make a drug that would bind to Sirt1 and fool the body into thinking that it needed to release that fat, then maybe people could get the benefits of calorie restriction without the side effects," he said, describing a sort of fountain-of-youth drug that he hopes to create.

How would such a drug work? Would it require vigorous exercise? Might there be additional complications in humans, such as reduced resistance to disease?

Evolutionarily, you would think it would make humans more resistant to infectious disease," Guarente said. But you never know."

He suspects that vigorous exercise also will be required. The next step in the process, he added, is to determine if an increase in Sirt1 in the body leads to a higher rate of metabolism.

This research was funded by the National Institutes of Health.

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