Low-Calorie-Diet Study Takes Scientists Aback
cientists 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."

http://www.nytimes.com/2003/09/19/science/19DIET.html