You're washing your hands, using Purell like crazy, and sneezing into your elbow. Now add these superfoods to your diet for an extra flu-fighting punch.

Flu-fighting foods

It takes more than an apple a day to keep the doctor away. It turns out that eating some pretty surprising nutrients will help keep your immune system on guard.

You can ensure your body and immunity run smoothly by rounding out your plate with plenty of colorful servings of fruits and veggies, plus 8 to 10 glasses of water a day, at the very least. The following ingredients can add extra flu-fighting punch to your winter meal plan.

Need more advice for staying healthy through the season? Check out Everything You Need To Know About Cold & Flu

1. Yogurt

Probiotics, or the "live active cultures" found in yogurt, are healthy bacteria that keep the gut and intestinal tract free of disease-causing germs. Although they're available in supplement form, a study from the University of Vienna in Austria found that a daily 7-ounce dose of yogurt was just as effective in boosting immunity as popping pills. In an 80-day Swedish study of 181 factory employees, those who drank a daily supplement of Lactobacillus reuteri—a specific probiotic that appears to stimulate white blood cells—took 33% fewer sick days than those given a placebo. Any yogurt with a "Live and Active Cultures" seal contains some beneficial bugs, but Stonyfield Farm is the only US brand that contains this specific strain.

Your optimal dose: Two 6-ounce servings a day. Here are 25 Tasty Things You Can Do With Yogurt

2. Oats and Barley

These grains contain beta-glucan, a type of fiber with antimicrobial and antioxidant capabilities more potent than echinacea, reports a Norwegian study. When animals eat this compound, they're less likely to contract influenza, herpes, even anthrax; in humans, it boosts immunity, speeds wound healing, and may help antibiotics work better.

Your optimal dose: At least one in your three daily servings of whole grains.

3. Garlic

This potent onion relative contains the active ingredient allicin, which fights infection and bacteria. British researchers gave 146 people either a placebo or a garlic extract for 12 weeks; the garlic takers were two-thirds less likely to catch a cold. Other studies suggest that garlic lovers who chow more than six cloves a week have a 30% lower rate of colorectal cancer and a 50% lower rate of stomach cancer.

Your optimal dose: Two raw cloves a day and add crushed garlic to your cooking several times a week.

4. Shellfish

Selenium, plentiful in shellfish such as oysters, lobsters, crabs, and clams, helps white blood cells produce cytokines—proteins that help clear flu viruses out of the body. Salmon, mackerel, and herring are rich in omega-3 fats, which reduce inflammation, increasing airflow and protecting lungs from colds and respiratory infections.

Your optimal dose: Two servings a week (unless you're pregnant or planning to be). Be sure to avoid these 12 Fish You Should Never, Ever Eat

5. Chicken Soup

When University of Nebraska researchers tested 13 brands, they found that all but one (chicken-flavored ramen noodles) blocked the migration of inflammatory white cells—an important finding, because cold symptoms are a response to the cells' accumulation in the bronchial tubes. The amino acid cysteine, released from chicken during cooking, chemically resembles the bronchitis drug acetylcysteine, which may explain the results. The soup's salty broth keeps mucus thin the same way cough medicines do. Added spices, such as garlic and onions, can increase soup's immune-boosting power.

Your optimal dose: Have a bowl when feeling crummy.

6. Tea

People who drank 5 cups a day of black tea for 2 weeks had 10 times more virus-fighting interferon in their blood than others who drank a placebo hot drink, in a Harvard study. The amino acid that's responsible for this immune boost, L-theanine, is abundant in both black and green tea—decaf versions have it, too.

Your optimal dose: Several cups daily. To get up to five times more antioxidants from your tea bags, bob them up and down while you brew. (5 more ways to maximize the health benefits of tea, here.)

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