Sci. Aging Knowl. Environ., 24 September 2003
Starting at any age, eating less extends fruit fly longevity
Key Words: demography dietary restriction age-specific mortality
It's never too late to change bad habits, at least for some insects. Fruit flies can lengthen their life by slurping less food, even if they don't start dieting until old age, according to new research.
Flies, worms, and mice that eat dramatically fewer calories outlive gluttons (see Masoro Review). However, mice gain time only if they moderate their munching by middle age. In adult fruit flies, continuous deprivation delays death, but once the flies start perishing, they keel over at the same rate as those at a perpetual banquet. Evolutionary biologist Linda Partridge of University College London and colleagues wanted to determine whether the life-span gain results from reduced cumulative damage, such as that inflicted by metabolic byproducts known as reactive oxygen species (see "The Two Faces of Oxygen"), or from some other factor.
The researchers postulated that if the life extension arose from reduced cumulative damage, bugs that went on a diet in middle age would begin dying later than those on a normal diet. And the late starters would die at a faster rate than insects that scraped along on slim pickings all of their lives. However, if all dieting flies died at the same rate, some risk factor other than cumulative damage must be to blame. To distinguish these possibilities, the researchers put almost 7500 adult fruit flies on diets, diluting their food by about 35% for various lengths of time. They determined the age at which flies started dropping like, well, flies, and how fast they died once they began.
Two groups of adult Drosophila gobbled their fill for 14 or 22 days and then cut back. These flies lived as long as flies that skimped the whole time--they started dying at the same time and died at the same rate. That result supports the hypothesis that the ascetic lifestyle doesn't work by reducing cumulative damage. To test whether the benefits of food dilution persist, the researchers did the converse experiment: They put another two groups of adult flies on a diet for 14 or 22 days, then switched the bugs to full meals. Insects that feasted after a famine died at the same rate as flies that had never dieted. The results suggest a short-term, increased risk of death for satiated flies--one that can be reversed by diet choice, says Partridge. She suggests that the unidentified, acute risk is the "physiological equivalent of crossing a road that has buses going 60 miles [96 kilometers] per hour on it. [On calorie restriction,] the flies stop doing that." The researchers haven't identified what speeds the flies to their graves, but it could be a nutrient, she says.
Calling the paper "remarkable and of wide importance," biodemographer Kenneth Wachter of the University of California, Berkeley, says the data "cleanly and for the first time" show that life extension is not due to reduced accumulated risk, at least in flies. Because the effect is sharp, the risk's biochemical origin should be relatively easy for researchers to find, he says. And when they do, perhaps the bugs won't have to starve to make life stop flying by.
September 24, 2003
Science of Aging Knowledge Environment. ISSN 1539-6150