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Low calorie diet study fruit flies { September 19 2003 }

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September 19, 2003
Low-Calorie-Diet Study Takes Scientists Aback

Scientists know that very strict low-calorie diets can prolong life. But now they report that it does not matter when you start that diet at least if you are a fruit fly. The life-prolonging effect kicks in immediately, continues as long as the diet, and is lost as soon as the dieting stops.

"We were very surprised, completely taken aback," said Dr. Linda Partridge, a professor at University College London, whose laboratory made the discovery.

For now, no one has a clue about what the crucial changes are in a fly's body when it goes on or off a diet. "It's been assumed that the reason things live longer when they diet is that there is a slowing down of age-related damage," Dr. Partridge said. But, she added, it now appears that cannot be true. "The system has no memory."

In a detailed demographic analysis of life and death among 7,492 fruit flies, published today in Science magazine, Dr. Partridge and her colleagues discovered that the protective effect of dieting snaps into place within 48 hours, whether the diet starts early in life or late. Flies that dieted for the first time in middle age were the same as flies that had been dieting their whole lives. But the effect can be lost just as quickly. Flies that dieted their entire lives and then switched, as adults, to eating their fill were the same two days later as flies that had never dieted.

Dr. Huber Warner, who directs the biology of aging program at the National Institute on Aging, said that it was as if dieting flies "put on a suit of armor."

"It seems like the dietary restriction puts the flies into a different kind of state where they are temporarily able to resist damaging events so that they survive rather than die," Dr. Warner said.

Dr. James W. Vaupel, a demographer at the Max Planck Institute for Demography in Rostock, Germany, said the findings put decades of research on the effects of calorie restriction in a new light. "We've known for a long time that dietary restriction increases survival," Dr. Vaupel said. "What we haven't known is that it's never too late."

It is a finding, he explained, that required huge numbers of flies to give the researchers valid data on death rates per day. That, in turn, allowed them to discover when the diet effect emerged.

Other studies, with flies, mice and rats, looked at survival curves, the chance that an individual will survive from birth to a particular age.

"You can see if an intervention is affecting survival over a period of time but not whether it is affecting mortality that day," Dr. Vaupel said. "You can't see whether there is a memory of all the bad things you've done in the past."

But, researchers said, previous studies are at least consistent with the new discovery. Rats and mice, for example, live about 30 percent longer when their diets are restricted and the dietary restriction can start in infancy or in middle age. They also found that if rodents are kept on restricted diets until middle age and then switched to eating what they want, they lose the life-prolonging effect of dieting.

It would take a study with as many as 500 rodents to see if dietary restriction has the same immediate effect in mammals as it did in fruit flies, Dr. Partridge said. But, at least in flies, she can now start asking what is happening to give the insects a suit of armor against whatever it is that might have killed them. Or, she said, "the more interesting question is, What is killing them when they eat too much?"

In an editorial accompanying Dr. Partridge's paper, Dr. Vaupel, Dr. James R. Carey, a biodemographer at the University of California at Davis, and Dr. Kaare Christensen, a professor of genetic epidemiology at the University of Southern Denmark, wrote that the message was that "for most species, aging is so remarkably pliable that interventions do not have to be lifelong."

"It's an encouraging message, even edifying," Dr. Vaupel said in a telephone interview. Of course, he added, not every bit of damage to the body can be erased.

"If you have a heart attack, permanent damage is done.," he said. "If you've had a detached retina, your vision is never going to be the same. But this doesn't mean there is nothing that can be done about old age. Even though there are some things you can't do anything about, current conditions are surprisingly important and more important than the legacy of all the bad things that have happened to you."

Copyright 2003 The New York Times Company

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