WASHINGTON - In a study on fruit flies, scientists have debunked the belief that fasting extends life spans in various organisms, including humans, when they suffer infection.

In their study, researchers at Stanford University School of Medicine wanted to see if reduced caloric intake also helps creatures cope with infection.

“Mounting a robust immune response is very energy-consuming. You might think an infected animal would be better off eating more, not less,” said Dr. David Schneider.

In the study on fruit flies, Schneider and his graduate student Janelle Ayres have shown that caloric restriction can indeed alter the flies’ response to infection, but in different directions depending on what they’ve been infected with.

The finding has potentially significant implications for humans, since flies are an excellent model system for studying certain aspects of our immune response.

In the study, the researchers measured the appetites of infected versus uninfected fruit flies, as well as the effects that restricting food intake in advance of an infection might have on flies’ response to the infection.

In an earlier research, Ayres had searched for mutant fruit flies that died faster, or more slowly, than normal flies after being infected with pathogenic bacteria.

One batch of mutant flies she identified were super-light eaters due to a faulty taste receptor.

These mutants were used for several of the experiments in the new study, and the researchers also repeated their experiments with normal flies that had been placed on caloric restriction for some time prior to being infected.

The observed results were the same in either case.

The investigators infected flies with three very different strains of bacteria, all of which can cause fatal disease in humans and then compared diet-restricted versus normally fed flies’ survival after infection.

Flies that had restricted caloric intake prior to infection with the pathogen, Enterococcus faecalis, ate no less than uninfected flies did. The “low-calorie flies” also survived for the same length of time as normal eaters.

When injected with S. typhimurium, flies on prior caloric restriction outlived normal eaters, surviving about 15 days post-infection versus eight days for the control flies.

Low-cal flies infected with L. monocytogenes, on the other hand, died faster than likewise infected normal eaters. They lived for only four days, as opposed to six or seven in the case of flies that had been on normal diets.

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

In their study’s conclusions, the authors write, “The work reported here should raise a cautionary flag, as it demonstrates that diet restriction can have complex effects on the realized immune response of a diet-restricted animal.”

The study has been published online in PLoS-Biology. (ANI)