Viagra for Flies?

Starve a fruit fly and it will live a longer, albeit practically celibate, life. But give these old coots a diet of protein and something amazing happens. The flies not only begin to reproduce, but they also appear to have a new lease on life. The finding, reported in today's Science, sheds light on how populations tough it out when protein is scarce.

Many biologists think that most organisms are genetically programmed to maintain themselves only until they've passed on their genes. Yeast and nematode worms, for instance, will enter a state of lowered metabolism similar to hibernation--and thus age more slowly--if food is too scarce to allow them to reproduce. Once they do reproduce, their bodies begin to decay. Now Jim Carey, an insect demographer at the University of California, Davis, and his colleagues have shown for the first time that this response exists in a more complex organism.

Carey has discovered that flies forced to subsist on sugar alone live in a "waiting mode." They tend not to reproduce and live 50% longer than the normal life-span of 60 days. This mode may allow animals to essentially stay young when there's not enough food available, Carey says. "You've got to wait it out 'til you get the chance to reproduce." In contrast, flies fed protein from birth matured quickly, reproduced with gusto, and tended to die young.

To figure out if elderly flies on the sugar diet are still fertile, Carey switched them to a diet that included protein when they were 30 days old, 60 days old, or 90 days old. Egg-laying went up, even in the very old flies. Surprisingly, the switch to protein also extended life expectancy--by 30% in the youngest treatment group, by 130% in the middle-aged, and by a whopping 1100% in the oldest flies. "Literally, changing diet was rejuvenating," Carey says. "It made the flies young again." Carey doesn't know the reason why.

This and similar findings can "provide very valuable clues to the fundamental process of aging," says Roger McCarter, a physiologist at the University of Texas Health Science Center in San Antonio, who has studied calorie restriction in rats and mice. He calls the new data "very provocative."

Posted in Biology