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 during this flu season — which may be a doozy — if you focus on a plant-based diet rich in whole unprocessed foods, Heller adds. One of the best eating patterns to illustrate this is the Mediterranean diet, which is rich in fruits, veggies, whole grains, nuts, beans and healthy fats like fatty fish and olive oil. A study published this past March in the journal Frontiers in Nutrition found that people who followed this diet were less likely to become infected by or die from COVID-19, suggesting it may provide an immune system boost that could protect you from other viral infections, too.
Here, more immunity boosting foods that research, and nutritionists, recommend for right now.
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 new meta-analysis published in July 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. But 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.
They’re a rich source of vitamin C, which stimulates production of infection fighting white blood cells, says Taylor. 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 so easy to incorporate them 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.
Why Wine is Not a Superfood This Season
As the holiday season approaches, keep in mind it’s also still flu season. For that reason, experts recommend you stick to moderate drinking — whether or not the champagne is flowing. (That’s one drink per day for women and two for men, says Cohen.)
Why: “Alcohol causes your liver to work overtime to detoxify your body, which means it’s not available to do its other important jobs like filtering bacteria and other toxins from the bloodstream and storing vitamins and minerals from food,” Cohen says. While research shows that excessive alcohol use clearly raises your risk of getting several serious conditions related to the flu, such as pneumonia and acute respiratory stress syndrome (ARDS), even moderate drinking in older adults can blunt your immune system’s power.
Chickpeas, black beans, kidney beans ... they’re all high in zinc, which helps boost your body’s production of white blood cells that can help fend off viruses such as the flu, Taylor says. “Zinc deficiency has been linked to immune system dysfunction,” she notes. Taylor recommends at least a half a cup of cooked beans three times a week. You can throw them into soups, chili, 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 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 Providence Saint John’s Health Center in Santa Monica, California. They also have more alpha linolenic acid — an essential fatty acid important for immune function — than any other type of nut.
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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 six-ounce salmon filet has about 600 IU of vitamin D, which is close to the 800 IU that is recommended 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.
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 adds.
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.
Hallie Levine is a contributing writer and an award-winning medical and health reporter. Her work has appeared in The New York Times, Consumer Reports, Real Simple, Health and Time, among other publications.