Need an excuse to delay your New Year's resolution diet just a bit? Cutting back on calories can make you more susceptible to flu, according to ongoing research at Michigan State University.
Since this flu season is shaping up to be a bad one, you may want to avoid starving yourself at the moment—particularly if you haven't had a flu shot.
In the U.S., flu season tends to peak in February, and flu symptoms include fever, muscle aches, cough, and a runny nose. Docs and emergency rooms are currently buckling under the impact of what seems to be an early and severe flu season.
In a 2008 experiment, Elizabeth Gardner, PhD, an associate professor in Food Science and Human Nutrition, found that mice put on a calorie restricted diet got sick more easily, had more severe symptoms, and stayed sick longer after being exposed to the influenza virus compared to mice fed a regular diet.
Now people aren't mice, but the results may still apply to humans (more on that later).
"Originally we thought the calorie restriction would help improve their immune systems, but we found the opposite was true," Gardner says. "More calories during flu season helped ward off the virus or if it didn't, it at least resulted in fewer symptoms and a speedier recovery."
Gardner says dieting mice suffered the most because they lacked the antibodies to fight off infection.
"Animals with fat stores have a source of energy to help fight off infection, but animals on a restricted diet start using sources other than fat like muscle and heart tissue, which weakens their defenses even further," Gardner says.
In her original study, Gardner wanted to find out how dieting might affect the immune response if the flu vaccine wasn't effective. She found that older mice and thinner mice fared the worst. In follow-up studies, she's since discovered that all mice have trouble fighting off the virus when they eat less. She's also found that even if they can manage to eat a full-calorie diet once they get sick, their defenses still lag behind those that eat well all the time.
Can the results really be applied to humans? Gardner thinks so. The dieting mice in the Michigan studies ate 20 percent to 40 percent fewer calories than their lab mates. As Gardner notes, many fad diets restrict calories by about the same amount.
She says cutting back on calories could have the same effect on humans and mice, making flu season the worst possible time to contemplate a diet.
"It's fine to restrict your calories during the eight months of the year when flu isn't a factor, but during those four months of flu season, you want to 'feed a fever,'" she says. "You'll stay healthier if you eat because you really want to have all your reserves to fight a virus."