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 says. 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 such as fatty fish and olive oil. A study published in 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. 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, 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 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.
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,” she explains. They’re 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, 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 6-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 says.
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 (found in tomatoes) is itself an antioxidant that helps the immune system she says.
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.
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.