A study on diet and life in the journal Science dealt only with laboratory fruit flies, but researchers said some of the same effects may apply to mammals, perhaps even humans.
In the study, British researchers compared the effects of different calorie-restricted diets on the mortality of fruit flies. They found that fruit flies on restricted diets lived about 90 days, twice as long as those fed on a normal diet.
But the scientists also found that when heavily fed fruit flies were switched at middle age -- day 14 to 22 -- to leaner diets, then the animals converted from the shorter life pattern of the overfed to the longer-lived pattern of flies that had been on a restricted diet all their lives.
The carry-home message from the study, said Linda Partridge of University College London is that it is never too late to improve health by switching to sensible eating habits.
"If this works in humans, then it means that from the time a person starts on a restricted diet, they'll be like individuals of the same age who were always on that diet," she said. "Their prospects of survival are the same."
Partridge said that although the life-extending effects of short rations have never been proven in humans, it has been shown in monkeys, mice, rats and fruit flies that diet restrictions will lead to longer lives.
"There is no reason to suppose it wouldn't apply equally to humans," she said. "There are diet restriction studies now underway with monkeys and all the indications appear the same [as with mice, rats and fruit flies]."
James R. Carey, a University of California, Davis, researcher who studies the biology of aging, said the Partridge study is "important to the field," but does not provide final answers about the true effects of restricted diets.
He said that fruit flies and other animals on restricted diets tend to stop reproducing. In mammals, for instance, the females stop ovulating and, hence, cannot reproduce.
As a result, Carey said, animals on restricted diets may live longer simply because they are not expending energy and stress in the rigors of reproduction. He said studies still need to specifically isolate and prove that it is the lean diet alone that leads to longer life, and not related factors.