Sci. Aging Knowl. Environ., 22 December 2004
Wild-like pattern of feast and famine extends Medfly life span
R. John Davenporthttp://sageke.sciencemag.org/cgi/content/full/2004/51/nf114
Even the most ascetic dieter occasionally succumbs to cravings for a bacon double cheeseburger or a pint of Ben & Jerry's Cherry Garcia ice cream. But according to a new study, frequent bingeing helps enhance the life-span-extending effects of a reduced-calorie diet--for Medflies, at least. The findings might help researchers craft a nuanced view of connections between diet and longevity.
Laboratory experiments have revealed that cutting calorie intake extends the lives of many species, including rats, mice, and fruit flies (see Masoro Review). But in the wild, animals don't enjoy the steady buffet that they do in the lab. Instead, they face periods of meager resources interspersed with moments of abundant fodder. Demographer James Carey of the University of California, Davis, and colleagues wondered whether natural patterns of food scarcity would extend life span as does the consistently harsh regime tested in the lab.
To investigate that question, the researchers fed groups of Medflies different diets. On each day of the experiment, they provided each fly either a "high-quality" protein and sugar meal or one that contained only sugar. The scientists used a mathematical model to specify which dish flies received over the course of the experiment. They arbitrarily assigned two parameters to each group: the probability that the insects would receive the rich entree and how many consecutive days they'd get that meal. In this way, they generated 12 different random patterns of diet that extended over 80 days. Each group received at most 80% as many calories as flies fed normally. In all cases, bugs on feast-or-famine diets outlived control insects that constantly gulped full meals. But among the flies on cycling diets, those that encountered hearty fare more often lived the longest. In addition, females who most frequently dined heavily also produced the most eggs. Life span and quantity of eggs depended more on how frequently flies switched from meager dinners to the rich one than on how long they binged. Previous studies revealed that Medflies continuously fed low-calorie meals don't survive especially long ("Not in Medflies"), and the new results suggest that life span depends not just on whether calories are scarce but also on more complex patterns of their availability. "It's more complicated than the conventional wisdom," says Carey.
The study tackles the "unexplored question" of how varying dietary patterns adjusts the life-extending effects of calorie restriction, says gerontologist Edward Masoro, a professor emeritus at the University of Texas Health Sciences Center in San Antonio. The results provide new information about how evolutionary forces have shaped animals' responses to lean times, says physiologist Roger McCarter of Pennsylvania State University, University Park. The work suggests that the cycles of feast and famine that occur in the wild select for individuals that go into survival mode when food is scarce, he says. Now, researchers should investigate whether similar patterns of rodent feeding perturb life span, he says. Such studies should clarify how real-world eating patterns shape longevity.
December 22, 2004
Science of Aging Knowledge Environment. ISSN 1539-6150