By Jennifer LaRue Huget
Tuesday, September 22, 2009
As we begin hearing of outbreaks of H1N1 flu, many of us are looking for ways to stay healthy this fall and winter.
Being a nutrition writer, I naturally figured food has got to help. Indeed, Googling "foods that boost immune system" turns up lots of lists: lists of the 8 foods, 10 foods, 12 foods, even 21 foods that promise to build your body's immunity. The idea is that consuming certain foods or particular nutrients helps your body protect itself from getting sick, no matter what nasty germs come its way.
If only it were so simple. If fending off infections were as easy as gorging on blueberries (for the antioxidants) or gobbling yogurt (for its helpful bacteria, or probiotics), many of us could sail through cold and flu season with nary a sneeze.
But experts agree that it's a lot more complicated than that. There's no single food -- or even group of foods -- that can be counted on to do the trick.
"The immune system is the result of an extremely complex interplay of various functions within the body," said Darwin Deen, senior attending physician in Montefiore Medical Center's department of family and social medicine in New York. "We know that if the system is deficient, you're susceptible to infection. That's the case with HIV. But we also know that if the system is hypersensitive, you'll have allergies, and if it's turned toward the wrong tissue, you have autoimmunity" -- where the body turns on itself. So efforts to "boost" the system, even through diet, might produce unintended consequences.
It's not reasonable to expect that one food will substantially enhance your immune response, Deen said.
"We haven't done a very good job of identifying nutrients that boost immunity," he added. "To say that there are nutrients that are important to the immune system implies that there are nutrients that are not important to the immune system."
In fact, more useful than eating certain foods is to eat "on a regular basis," Deen said. "Every time you eat something, you're asking the immune system to respond to what you put in your mouth." The idea is to "keep the immune system busy" so it's ready to leap into action when you need it most.
In particular, Deen said, eating protein encourages the body to "generate antibodies used by the immune system."
In any case, good hygiene is far more important to fending off a virus than eating certain foods. "You can't drink a glass of orange juice before school and say, 'Now I don't have to wash my hands,' " Deen said.
Christine Gerbstadt, a physician and registered dietitian in Sarasota, Fla., and a spokeswoman for the American Dietetic Association, says the familiar prescription of a well-rounded, healthful diet can provide the central nutrients your body (including the immune system) needs to stay healthy.
She suggests "quick, small combinations" of a variety of useful foods: "Have some whole-grain bread with vegetables and low-fat cheese, add some cucumbers, tomatoes, mushrooms, cabbage or red pepper, and it's easy to get all the building blocks." And don't be swayed by immunity-boosting claims of the latest super-foods, be they almonds or blueberries, pomegranates or strawberries. They're generally backed by trade groups, she says, whose focus is narrow -- and self-serving.
Finally, Gerbstadt notes some recent interesting research: In one study, overweight rats whose calorie intake was severely restricted experienced improved immune function. In another, mice that consumed a high-fat, high-sugar diet saw that function reduced. Those findings, if replicated in humans, could provide yet another reason to lose weight and eat less junk food.
In the meantime, food remains just part of the equation. Aside from flu shots, "living right, washing hands and taking care of yourself are the best immune defenses," Gerbstadt says.
Mark Kantor, an associate professor of nutrition and food science at the University of Maryland's College of Agriculture & Natural Resources, agrees with Deen's and Gerbstadt's approach.
"My feeling is that you need to have a healthy diet in general to have a generally healthy immune system," he says. "Sure, there are some nutrients known to play a role," including the antioxidants Vitamin E and Vitamin C, the minerals selenium and zinc, Vitamin D and fish oils containing omega-3 fatty acids. "Yes, these nutrients are important, but that doesn't mean that eating lots of them will necessarily boost your immune system."
While Vitamin C and zinc, for instance, clearly are vital to the immune system, Kantor said, "we don't have widespread deficiencies" of those nutrients, so most of us don't need to intentionally consume more. Plus, he said, "I don't think there's any evidence that higher doses of these reduces the risk of getting sick."
Kantor suggests that we look instead at "which key nutrient you're not getting enough of in the first place." For most people, he said, those include the omega-3 fatty acids (found in fish oils, they help protect against inflammation, which Kantor said is closely linked to immune response) and Vitamin D, in which recent research has shown most people are deficient.
"Really, there's not that much you can do in terms of your diet to protect yourself against the H1N1 virus" or any other such bug, he said. "As much as people want to believe otherwise, if you catch it, you're going to get it."
Check out Tuesday's Checkup blog post, in which Jennifer solicits ideas for foods to help you feel better if you end up sick after all. Subscribe to the Lean & Fit newsletter by going to http://www.washingtonpost.com/health.