Maybe it is time to give up steak in order to live longer—at least if you are a fruit fly. According to a study published today in Science, a diet of sugar keeps flies in a metabolic "waiting mode," in which both reproduction and death rates are low. But if the flies are switched to a protein diet (which is scarce in nature), they switch to a reproductive mode in which mortality is initially low but increases sharply as more eggs are laid. Fascinatingly, if the flies are alternated between the sugar and protein regimens, switching back and forth between waiting and reproductive modes, they live longer than flies kept exclusively in either mode. It has long been known that dietary restriction can prolong life in rats and nematode worms. This latest finding, in the geneticist's favorite laboratory model, may help elucidate the physiological underpinnings of longevity.—June Kinoshita
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