LIFE-SHORTENING AROMA: In fruit flies, scientists have determined that the smell of food can have a negative effect on caloric restriction diets, generally designed to impart a longer life. Image: © STOCKBYTE/CORBIS
Evidence began mounting as long as 70 years ago that restricting calories while consuming necessary amounts of sustenance could increase one's life span. Since then, a group called the North Carolina-based Calorie Restriction Society has sprouted whose 1,800 members routinely down about half of the daily caloric intake recommended by the Food and Drug Administration (FDA) in the hope of living to the ripe old age of 120.
New research may prompt the organization to send out nose plugs with its next newsletter.
A team of scientists at the Baylor College of Medicine in Houston, New Mexico State University at Las Cruces and the University of Houston found that the average life span of fruit flies on restricted diets decreased when they were exposed to food odors. The findings, according to lead researcher Scott Pletcher of Baylor's Huffington Center on Aging, suggest that the flies are "actually perceiving the environment," thinking they are in a nutrient-rich place and then their bodies are "adaptively responding to it." The results imply there is likely some olfactory component affecting humans on caloric restriction diets as well.
Pletcher's group exposed two lab strains of fruit flies on caloric restriction to smells created by live yeast, an important constituent of the fly's diet. These flies died three to 10 days sooner—a 6 to 18 percent reduction in life span—than flies on the same diet that did not get a whiff of the yeast. Their life spans were further shortened if the flies actually ate the yeast paste.
Pletcher says the smell of yeast only had an effect on the life spans of dieting flies and not on those that were fully fed and likely already perceived their immediate environment to be nutrient-rich. "If you're in what might be considered an alternative physiological state that is associated with long life span under diet restriction, then the foods have some effect," he says, noting "that suggests that there's some interaction because the odorants aren't having the same effect in all environments."
To determine if smell alone has an effect on longevity, Pletcher's team created a fruit fly strain that had a particularly sensitive olfactory receptor inhibited. Fully fed female flies with an impaired sense of smell exhibited an average life span increase of 56 percent compared with unaltered wild females. Males also lived longer than their wild counterparts. Pletcher says this indicates that odor-mediated aging and dietary effects on aging probably share some of the same physiological pathways.
Brown University ecologist Marc Tatar says the current study, published in this week's Science, provides "really profound evidence" that longevity is controlled not by actual resources but rather by hormones that are cued to resources (such as the way plants sense winter by sunlight changes). "It's like the whole system doesn't actually function on the currency of resources anymore, it all functions on virtual data about what the resources should be like," he says. "It's mind over matter."
Pletcher agrees with that analysis, at least in part. "Some component is due to perception," he says, "and another large component is actually consumption." But given the effect that eating versus smelling yeast had on longevity, he says, "Overall, I would guess consumption has a bigger effect than perception, that's for sure."