Many people, when they are feeling miserable from a cold or the flu, get the urge to gorge on food. But picking the right foods can benefit and even speed healing.
"This is more or less a new area," said Kerry Neville, a Seattle dietitian and spokeswoman for the American Dietetic Association. "There has been some good research, and we'll be seeing more. But it remains to be seen how much of this can actually be helpful."
Teasing out how and where food can benefit is difficult because our immune systems -- a coordinated system of signals sent and received, feedback loops and multiple redundancies to ensure that foreign molecules are identified and destroyed if they are harmful -- are so complex. A breakdown in any part of the system leaves the whole body susceptible to infection and illness.
And lifestyle and environment can cause small breakdowns in the system all the time. Smoke, air quality, sunlight and poor diet can all contribute to a weakened immune system, particularly in the form of free radicals. These highly reactive molecules with unpaired electrons can break down cells, leaving them vulnerable to invading viruses and bacteria.
Antioxidants, a type of chemical found in plants, help neutralize free radicals and protect cells, thus bolstering the immune system. Antioxidants often give plants their color and can also include vitamins C, A, and E. Experts estimate that there are many more antioxidants that are as yet unidentified.
And studies have shown that some of the protective vitamins and minerals, when given alone, do not benefit people as much as getting those nutrients from their diets.
"I don't say any one food is going to protect you," said Dawn Jackson Blatner, a registered dietician and author of "The Flexitarian Diet." "There is a crazy thing that happens, and it is called synergy. ... You start putting multiple [foods] together, the effects are multiplied and it is shocking."
The nutrients in food are not meant to be consumed in a vacuum. The context in which the body encounters the healthy minerals and molecules is almost as important as the nutrients themselves, which may be why chicken soup is such a popular home remedy.
"It's the recipes that have the magic, just the way the foods are combined," said Dr. John La Puma, author of "Chef MD's Big Book of Culinary Medicine." "If you just eat one food and expect it to act like a drug, you're out of luck."
But prevention is not the name of the game for most of these foods in targeting a specific illness. Once ill, the expert advice boils down to fluids, rest and eating a variety of healthy food.
"Nothing is a magic bullet, as far as making a major impact in making you feel better as quickly as possible," Neville said.
Some dietitians do recommend taking a daily multivitamin because, as Neville pointed out, people do not typically eat as many fruits and vegetables as they should -- around two to three cups per day.
Over all, maintaining a diverse diet, rich in fruits, vegetables, whole grains and lean protein, is the body's best defense against viral invaders.
Following are some foods to focus on to help boost your immune system when feeling under the weather.