Diving Deeper Into the Fountain of Youth

Some people believe that calorie restriction is the surest way to a longer life, but a new study suggests that the quality of one's diet may be just as important. Fruit flies that cut calories by dropping yeast from their diet lived much longer than flies who left sugar off their plates, indicating that some nutrients may play a larger role in lifespan than others.

Studies have shown that a calorie-restricted diet increases longevity in several species, from yeast to mammals. This has prompted researchers to speculate that there is a single, evolutionarily preserved mechanism tying diet to lifespan. Although no one has proven that such a mechanism exists in humans, some stalwart longevity-seekers are already following severe diets in the hopes that calorie restriction will see them through to a very old age.

To determine how important calories themselves are in this equation, a team led by evolutionary geneticist Linda Partridge of University College London, tested the effects of various diets on fruit fly lifespan. A standard fruit fly diet in the lab consists of only two components: sugar and yeast. The team found that restricting yeast from birth caused flies to live 65% longer than controls, while cutting back on sugar extended their lives by only about 9%. In addition, the flies lived longer even if they switched to a yeast-restricted diet in adulthood, suggesting that the benefit of the new diet is immediate, the team reports 30 May in PLOS Biology.

"It's not just the calories which are important in the extension of lifespan, it's what you eat," says Partridge. Specific nutrients, like the protein and fat found in yeast, may affect lifespan more than others, she says.

Sige Zou, a geneticist at the Gerontology Research Center at the National Institute on Aging, said that the study lays the foundation for studying genes in fruit flies that respond to different nutrients. But Leonard Guarente, a molecular biologist who studies the genetics of calorie restriction at MIT, believes that the researchers may not have accurately measured calorie intake, which he says would involve measuring the exact amount of each kind of food the flies ate as well as their metabolic output. "I still believe the calories will turn out to be the currency," he says.

Related sites
The study
The Partridge Laboratory
National Institute of Aging
National Institute of Aging-sponsored clinical trial on calorie restriction