Flu season is upon us, and this year Americans face both seasonal flu and the H1N1 virus. An estimated 36,000 people die from the flu annually, and several hundred thousand are hospitalized, according to the Centers for Disease Control and Prevention.
When most people have the flu, the last thing they want to do is eat. However, research conducted by MAES nutrition immunology scientist Elizabeth Gardner suggests that consuming more calories during flu season could help ward off the virus and/or result in a speedier recovery.
Using a mouse model, Gardner and members of her laboratory are exploring the effects of caloric restriction on the primary immune response to influenza infection. Caloric restriction is the practice of reducing the intake of calories while maintaining adequate vitamins and minerals.
“Initially we thought caloric restriction would be desirable in fighting the flu because it extends life span, and one of its benefits is improved immune function,” Gardner said. “So we hypothesized that calorically restricting the animal would improve its immune function. We found the complete opposite was true.”
Gardner’s research showed that mice on a calorie-restricted diet were more likely to die during the first few days of infection than mice on a normal diet.
Individuals who are infected with the flu virus don’t have antibodies to fight the infection, Gardner said. The body relies on cells that recognize the virus and try to kill it. These natural killer cells, which draw on the body’s energy stores, act as the first line of defense in the fight against viruses.
“Our studies showed that, with caloric restriction, the natural killer cell response is reduced in older mice, so the virus is more likely to accumulate,” she said. “We wanted to find out how to improve the immune response when the vaccine isn’t effective.”
In Gardner’s research, both regularly fed mice and calorically restricted mice exposed to the virus exhibited decreased food intake as they tried to fight off infection. Yet the mice on calorically restricted diets took longer to recover and exhibited increased mortality, weight loss and other negative effects. Although both sets of mice took in appropriate vitamins and minerals, the mice consuming normal amounts of food recovered faster.
“Animals with fat stores have a source of energy, but calorically restricted animals have to start using sources other than fat, and that really has a taxing effect,” Gardner said. “It’s fine for adults to restrict their calorie intake eight months out the year, but during the four months of flu season, they need to have reserves in order to fight a virus.”
Gardner said that the flu vaccine has a 70 percent to 90 percent efficacy rate in young people, but seniors have a much lower response, so they are at greater risk for complications such as pneumonia. The CDC includes a significantly larger at-risk segment of the population for the H1N1 virus – including children and youth ages 6 to 24 – compared to seasonal flu viruses.
“Flu shots don’t guarantee protection because they are formulated months in advance and with the hope that the vaccinating strains are similar to those that might infect the population,” Gardner said. “With new threats such as the H1N1 virus, people should take every precaution they can to stay healthy. At-risk populations should increase calories but not fat intake, eating foods high in protein and antioxidants.”
Gardner now is investigating the mechanisms responsible for decreased immune function during caloric restriction and hopes her research in nutritional immunology will lead to a better understanding of how diet affects the immune system and the best conditions for a body to quickly and successfully fight infections.
The bottom line this flu season?
“Use nutrition to your benefit,” Gardner said. “If you get the flu, try to eat through it.”
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