Long Life Span in Flies Reversed By Just Whiff of Food

Mason Inman
for National Geographic News
February 1, 2007
Flies on a diet live much longer than flies that are allowed to eat all
they want. But just a small whiff of extra food is enough to shorten the
lives of the dieting flies again, a new study shows.

The effect only occurred in flies on restricted rations, though.

When flies could eat their fill—and thus already had shortened lives—smelling more food didn't cut their lives any further.

The research, led by Scott Pletcher of the Baylor College of Medicine in Houston, Texas, confirms a strong connection between smell and life span.

The study will be published tomorrow in the journal Science.

Healthy Diet

Many animals—from monkeys to mice to microscopic worms—live longer when they eat less than their fill. (Related: "Discoveries May Help Unlock Secrets of Long Life" [October 30, 2003].)

The effect may occur because animals are genetically programmed with strategies for dealing with food shortages.

During famines, for instance, they could put more of their energy into repairing their bodies and living longer.

But when a cornucopia of food abounds, the animals put their energy into making babies.

At normal food levels, for example, flies live about 45 days. When they can eat as much as they want, the flies only last about 35 days. But when they're on the optimal diet, they live about 55 days—about 60 percent longer.

The smell of food erased about a quarter of the gain they got from dieting, though.

Smell of Death

Earlier studies had showed that restricting flies' diets could change their death rates rapidly, which led scientists to suspect that smell was playing an important role.

"Once they started [eating] healthily, their mortality rates dropped within a day," Pletcher said. "This was sort of striking and showed they could adapt to their environment very quickly."

Oddly, it's as though the flies' brains don't listen to their stomachs, he added. Instead, the animals rely mostly on smell to tell them how much food is available.

In the new study, mutant flies with damaged sniffers lived longer regardless of their diet and also escaped the ill effects of smelling food. In fact, these flies lived about 75 days—the longest of all.

But it's not yet clear what the new findings might mean for people, Pletcher said. (Related: "Happy 120th? Science Pushes Human Longevity" [October 20, 2005].)

Aging Puzzle

The study also illustrates how aging is not just an inevitable decline and breakdown.

Instead, animals can subtly and unconsciously control how fast they age depending on what they see—or smell—is happening in the environment.

The new study didn't find any strong link between life span and the number of eggs that the flies produced.

But living longer might still be affecting their reproduction, said Daniel Promislow, a geneticist at the University of Georgia in Athens.

Often these differences only show up in stressful conditions, which weren't explored in the new study, Promislow said.

"The flies may lay fewer eggs under stressful conditions," he added. "Or there may be some other tradeoff. The quality of the eggs that they lay can be lower."

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