A new British study offers hope for all those procrastinating dieters out there.
The study, published in the Sept. 19 issue of Science, found that reducing dietary intake late in life reduced mortality in fruit flies.
"We found that within just 48 hours of being switched from a high nutrient intake to dietary restriction, flies were no more likely to die than those that had been under dietary restriction constantly throughout their adult life," says one of the study's authors, Linda Partridge, a professorial fellow in the department of biology at University College London.
Partridge says it's impossible to know from this study if cutting back on calories could extend life in humans. However, she adds, "lifestyle interventions started as late as middle or old age may be beneficial."
For this study, Partridge and her colleagues studied almost 7,500 Drosophila fruit flies. In one experiment, flies were either "fully fed," constantly on a restricted diet, or fed a restricted diet from day 14 or day 22.
The restricted diet contained about 35 percent less nutrients than the fully fed diet, according to the study.
Fully fed flies lived about 32 days. Flies constantly on a restricted diet lived nearly 50 days. Flies switched from being fully fed to a restricted diet on either day 14 or day 22 also lived an average of almost 50 days.
In another experiment, the researchers reversed the dietary restrictions and started some of the flies on a restricted diet, and then on day 14 or day 22 switched them to a fully fed diet. Mortality rates dropped in the flies switched to a fully fed diet. Those switched on day 14 lived about 38 days and those switched on day 22 lived about 42 days. Had these flies stayed on the restricted diet, they would have been expected to live about 50 days.
"Current behavior and conditions appear to determine mortality," says James Vaupel, director of the Max Planck Institute for Demographic Research in Rostock, Germany. Vaupel wrote an accompanying editorial that appears in the same issue of Science.
"It used to be thought that you died from your whole life," he says. "It is certainly true that the damage done to your body by your whole life is of some importance, but surprisingly, it seems that current conditions are more important than the cumulative effect of past conditions. Today seems to be more important than your whole life."
Partridge says the researchers don't know why restricting the diet had such a dramatic effect on mortality. In the past, she says, researchers have hypothesized that dietary restriction increases the life span because it slows down the damaging effects of processes, like oxidation, that occur as food is digested. But Partridge says this theory can't explain why flies changed to restricted diets later in life did just as well as those who had been on restricted diets their whole lives.
"Dietary restriction late in adulthood is just as beneficial to the middle-aged flies as if they had been on it throughout adult life," says Partridge.