People who diet during flu season may have a harder time fighting off infection, new research suggests.

At Michigan State University, two groups of mice were exposed to a flew virus. One group had been fed a normal diet. The other had been given reduced calories.

Both groups showed decreased food intake as their bodies tried to fight off infection. But the mice with restricted calories took longer to recover and showed higher mortality, weight loss and other negative effects.

Even though both sets of mice had a diet fortified with appropriate vitamins, the mice consuming normal amounts of food had their appetites back sooner and recovered faster, said Michigan State nutritional immunology professor Elizabeth Gardner, who conducted the study.

“Our research shows that having a body ready to fight a virus will lead to a faster recovery and less severe effects than if it is calorically restricted,” she said. “Adults can calorically restrict their diet eight months out for the year, but during the four months of flu season they need to bump it up to be ready. You need the reserves so your body is ready for any additional stress, including fighting a virus.”

Gardner’s research was published in the November issue of the Journal of Nutrition.

Gardner defined “caloric restriction” as the practice of reducing the intake of calories to 40 percent of a normal diet, while maintaining adequate vitamins and minerals.

Calorically restricted diets in general have been shown to increase lifespan in everything from yeast to primates. But Gardner said the model used in her research can be extended to more vulnerable groups, including children and the elderly, who don’t eat as much but often take vitamin supplements.

Flu shots can’t guarantee protection, she said, because they are formulated months in advance and can target only a handful of the many flu virus strains that might infect the population.

“If the strain of flu a person is infected with is different from the strain included in the flu vaccination, then your body sees this as a primary infection and must produce the antibodies to fight it off. A calorically restricted body is not as well prepared to do this and cannot control early infection, which impedes recovery,” Gardner said.

 

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