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Study: Even mid-life diet change can extend life

Friday, September 19, 2003 Posted: 8:41 AM EDT (1241 GMT)

WASHINGTON (AP) -- It has long been known that laboratory animals

live longer on a low-calorie diet. Now a study suggests that even if

sensible eating is delayed until middle age, health can be improved

and life extended.

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 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]. "

R. Carey, a University of California, , 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.

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