Listening to the body: Study examines the effects of fasting on infections

The study also suggests a biological basis for certain food preferences during illness. It was published Sept. 8 in Cell.

For decades, scientists and doctors have speculated about the effect of certain sickness behaviors, such as fasting, on the immune system and on the course of disease. To investigate the phenomenon, a Yale research team, led by immunobiologist Ruslan Medzhitov, observed the impact of nutrition on mice infected with common viruses or bacteria.

"When animals are infected they stop eating and they switch to a fasting metabolic mode," Medzhitov said. "The question was whether fasting metabolism is protective or detrimental."

When the researchers fed the animals, they found that those with viral infections survived, but the bacterially infected ones succumbed to the illness. By testing individual nutrients (fat, protein, and glucose), they determined that glucose was responsible for the opposing effects of nutrition on infection.

The team then repeated the experiment, but used chemicals to block the glucose metabolism. The results were reversed: Mice infected with bacteria survived, and mice infected with viruses did not.

The differing effects of nutrition on viral versus bacterial infections may be explained by differences in the immune response, the researchers said. Bacterial and viral infections cause different types of inflammation that can cause tissue damage. Depending on the cause of infection, nutrition can either help or hinder the body's ability to tolerate inflammation.

"During a viral infection, eating provides glucose, which may be necessary for survival," Medzhitov said. Conversely, fasting leads to the production of ketones -- another type of fuel -- which may help animals tolerate a bacterial infection, he said.

The study suggests that different diet preferences may correlate with different types of infections, the researchers noted. Although further research is needed, the findings may have implications for how clinicians feed patients suffering from acute infections in intensive care units.

The findings provide support for the old adage "Starve a fever, feed a cold"; however, the authors caution that this should not be taken literally, as the effect may depend on the specific infection.

"Through millennia, all organisms evolved to be attuned to what cells need," said Andrew Wang, M.D., first author and a clinical fellow in medicine. Cells require certain nutrients to perform tasks, he noted, and food preferences may be the body's way of telling us how best to survive different types of infections.

Other Yale authors include Sarah C. Huen, Harding H. Luan, Shuang Yu, Cuiling Zhang, Jean-Dominique Gallezot, and Carmen J. Booth.

The work was supported by the The Blavatnik Family Foundation, Else Kröner Fresenius Foundation, Howard Hughes Medical Institute, and grants from the National Institute of Health.