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Not so fast

Not so fast

Study adds wrinkle to fasting-longevity research

Study after study seems to show that lab animals live longer if they stay hungry, leading many to conclude that restricting calories slows aging in humans too. But microbiologist David Schneider, PhD, wanted to see if this held true in the real world.

At the root of his skepticism was this: Virtually all of these studies on diet restriction had been performed in sterile environments, on animals raised under relatively pathogen-free conditions. Schneider, an associate professor of microbiology and immunology, and his then-graduate student Janelle Ayres, PhD, wondered whether the apparent starvation advantage would persist if the animals were exposed to germs that left them seriously under the weather.

“There’s evidence that caloric restriction seems to rev up various individual components of the immune system,” he says, “but in the few previous studies where diet-restricted animals actually have been infected experimentally, they fared poorly.”

So Schneider and Ayres offered their lab animals — several thousand fruit flies, in this case — a dose of reality along with their meals. They injected them with microbes that make both flies and people sick, and they observed whether hungry flies survived infection more successfully than well-fed ones. The outcome could have significant implications for humans, says Schneider, since flies are an excellent model system for studying certain aspects of our immune response.

The results, published online July 13 in PLoS-Biology revealed the answer: It depends.

The investigators infected flies with three very different strains of bacteria, all of which can cause fatal disease in humans. Then they compared the survival of diet-restricted flies versus that of normally fed ones after infection.

Flies that had restricted caloric intake prior to their rendezvous with the pathogen Enterococcus faecalis survived for the same length of time as normal eaters. But dieting flies injected with Salmonella typhimurium had longer lives than likewise infected flies who ate normally: The low-cal flies survived 15 days post-infection versus eight days for the control flies. Low-cal flies infected with Listeria monocytogenes, on the other hand, died faster than the controls. They died after only four days, as opposed to six or seven in the case of the flies that had been fed normal diets.

The Schneider lab is seeking physiological explanations for this divergent response. But taken as a whole, the results so far suggest that some skepticism might be in order regarding climbing aboard the caloric-restriction bandwagon, Schneider says.

His study shows there may be something to the celebrated admonition “feed a cold and starve a fever” after all. But much remains to be learned about exactly which infections can be fought best by gorging and which by fasting.

The work was funded by grants from the National Institutes of Health, the National Science Foundation and the Ellison Medical Foundation.

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