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Superfoods for Flu Season

What to eat or drink to build a stronger defense this winter

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The saying “you are what you eat” applies to your entire body, but it’s especially important when it comes to your immune system during flu season. “As we get older, our immunity starts to decline, but if we get the right nutrients, we can help our immune systems do their jobs to protect us against viruses like the flu,” says Samantha Heller, a New York City nutritionist.

You can keep it in tip-top shape this flu season — which may be a doozy — if you focus on a plant-based diet rich in whole, unprocessed foods, Heller says. 

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Here are eight foods that nutritionists recommend for flu season.

1. Green tea

Whether these particular tea leaves can really fend off the flu has been a source of debate among health researchers for years. But a meta-analysis published in July of 2021 in the journal Molecules looked at more than eight studies involving more than 5,000 participants to conclude there really is ample evidence to believe the beverage — and specifically, the catechins that provide its antioxidant power — can help your immune system fend off influenza.

2. Sweet potatoes

They’re a great source of beta-carotene, a phytonutrient that helps your body make vitamin A. “It supports respiratory health by increasing the number of immune cells in the body,” explains Anna Taylor, lead outpatient clinical dietitian at the Cleveland Clinic’s Center for Human Nutrition. This is especially important for older adults, as our bodies make fewer immune cells as we age, she adds. 

Instead of cooking them with butter or brown sugar, Taylor recommends that you roast them with olive oil, oregano and black pepper. “You’ll get additional benefits from the spices, but you’re not loading up on sugar and saturated fat, both of which suppress your immune system,” she says.

3. Berries

They’re a rich source of vitamin C, which stimulates production of infection-fighting white blood cells, Taylor says. A 2018 review of studies found that berries increased levels of disease-fighting cells in older adults, such as natural killer cells and T-cells. They also contain flavonoids, substances that have antioxidant properties and protect all your cells — including your immune system cells — from damage, she adds. 

It’s easy to incorporate berries into your diet: “Add them to your morning yogurt or oatmeal, or even cook them and throw them on your French toast instead of maple syrup,” Taylor recommends.

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4. Beans

Chickpeas, black beans, kidney beans — they’re all rich in vitamin B12, a nutrient many older adults are low in, Heller says. “People over the age of 50 don’t absorb vitamin B12 as well in their body, but your immune system needs it to fight disease and repair damaged cells to keep you healthy,” Heller explains. 

Why Fluids Matter if You Get the Flu

Whether water, electrolyte-rich beverages, broths or green tea (see above), you really do need liquids if you’re sick with the flu. Not only is it important to fend off dehydration, staying hydrated helps you maintain enough circulating blood volume to treat infection. (Just go easy on the caffeinated sodas and coffee.)

And yes, doctors say chicken soup can’t hurt, since fever can cause you to lose water as well as salt.

Beans are also high in zinc, which helps boost your body’s production of white blood cells, Taylor says. “Zinc deficiency has been linked to immune system dysfunction,” she says. Taylor recommends at least a half a cup of cooked beans three times a week. You can throw them into soups, salads or even rice dishes. For a healthy crunchy snack, roast chickpeas in some olive oil.  

5. Nuts and seeds

These foods are rich in vitamin E, which plays a key role in your immune system by supporting the growth of germ-fighting T-cells, says Lauri Wright, chair of the Department of Nutrition and Dietetics at the University of North Florida. They’re also a good source of omega-6 fatty acids. Walnuts are an especially good choice, as research shows they have a very positive effect on your gut microbiome, says Kate Cohen, a registered dietitian nutritionist with the Ellison Institute for Transformative Medicine at the University of Southern California. They also have more alpha-linolenic acid — an essential fatty acid important for immune function — than any other type of nut.

6. Salmon

It’s not plant-based, but it is one of the few foods that provides vitamin D, which plays a huge role in regulating your immune system, says Jennifer McDaniel, owner of McDaniel Nutrition Therapy in Clayton, Missouri. A 2020 study published in the journal JAMA Network Open found that people who had untreated vitamin D deficiency were almost twice as likely to test positive for COVID-19 as patients who had sufficient levels of the vitamin. A 6-ounce salmon filet has about 600 international units (IU) of vitamin D, which is close to the 800 IU that is recommended daily for people 70 and older. Another bonus: It’s rich in omega-3 fatty acids, which have also been shown to strengthen your immune system.

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If you’re not a fan of fish, McDaniel suggests marinating it in brown sugar and Dijon mustard for 45 minutes, then throwing it on the grill. “It mellows out that fishy taste, and it gives it a smoky flavor,” she explains. Canned salmon counts, too: Throw it over a salad for a quick meal, she says. 

7. Garlic

It’s rich in a compound called alliin, which may be the source of its immune-boosting properties, notes Libby Mills, a Philadelphia nutritionist and spokesperson for the Academy of Nutrition and Dietetics. A 2020 review published in the journal Medical Hypotheses found that garlic itself seems to stimulate cells related to immune system function. Another study published in the Journal of Nutrition found that people given about 2½ grams of aged garlic extract for 90 days not only had higher levels of immune system cells, but they also had fewer symptoms of cold and flu, and missed fewer workdays due to these respiratory illnesses, than a control group. At the very least, if you eat enough of it, you’ll probably keep people away from you, Mills jokes.

Although there’s probably not enough research to support taking a garlic supplement, Mills recommends that you cook with it in the colder winter months. You can make your own pasta sauce with tomatoes and garlic, since vitamin C is itself an antioxidant that helps the immune system she says.

8. Kefir

Recent research, including a 2021 study published in Biomedicine & Pharmacotherapy, suggests that certain compounds found in fermented dairy such as kefir (which is like a thin yogurt) have anti-inflammatory properties that can help the immune system fight viral infections. The probiotics found in kefir and other fermented foods also help to calm chronic inflammation, according to Harvard Health. “Fermented dairy is rich in probiotics, which seem to have a positive effect on the immune system,” Mills explains. 

Editor's Note: This story, published Nov. 1, 2021, has been updated to reflect new information. 

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