Healthy, balanced immune function is your best defense against any illness. One of the keys to bolstering your immune system? Nutrition.

“Diet is all-important,” says preventive-medicine specialist David Katz, MD. “You’re building white blood cells, enzymes, and antibodies every day, and the food you eat is literally the source of your construction materials.”

A single meal can alter how immune cells respond to provocation, and the effects accumulate over hours, days, and weeks, he explains. “You can do a complete 180 and optimize a badly broken immune system in as little as weeks by improving your diet, so it’s a very immediate return on investment.”

Foods that dampen the immune system include highly processed or fried foods, those high in added sugar, and nonorganic foods grown with glyphosate, the chief ingredient in Roundup, a common herbicide that has been linked to cancer.

On the flip side, foods rich in polyphenols — beneficial plant compounds found in many vegetables, fruits, and legumes — support immune function. Integrative practitioner Robert Rountree, MD notes that the Mediterranean diet (plenty of colorful vegetables, nuts, and olive oil; moderate amounts of protein; and a little red wine with dinner) provides a good general template for immune-supportive eating.

Some immune system–balancing superstars to focus on:

1. Green tea is rich in polyphenols, including potent antioxidants called catechins that have antimicrobial properties and may help protect against influenza. It also contains quercetin, a flavonoid that Rountree calls a “time-honored immune-supportive agent.”
2. Berries are a potent source of immune-supporting flavonoids. “When you eat berries, most of these pigment molecules go to the colon, where bacteria break them down into smaller molecules that escape and circulate in the body, exerting antiviral effects,” says David Nieman, DrPH, FACSM, an exercise immunologist at North Carolina’s Appalachian State University.
3. Turmeric gets its deep orange-yellow from curcumin, a compound that helps balance the immune system. It has a modulating effect on T cells, B cells, macrophages, and other immune cells, and can also enhance antibody response.
4. Garlic contains sulfuric compounds with a range of antimicrobial effects, such as inhibiting the biofilm formation of bacteria. It also has natural antiviral properties and can help reduce hypertension, one of the leading risk factors for COVID-19. (For more on garlic, see “Garlic”.)
5. Citrus fruits such as grapefruit, kiwi, and lemon deliver abundant ­vitamin C — one of the most important nutrients for the immune system, aiding in the formation of white blood cells. (For more on this essential ­nutrient, visit “What You Need to Know About Vitamin C”.)
6. Sauerkraut and other fermented foods contain lactic-acid bacteria, which produce compounds in the gut that spur the immune system into action. And cabbage itself is another excellent source of vitamin C.
7. Medicinal mushrooms are rich in beta-glucans, an immunomodulator that activates macrophages, natural killer cells, dendritic cells, and neutrophils. “Mushrooms like shiitake, oyster, and maitake have been shown to prime immune cells in published studies,” says Rountree. He recommends both eating shiitake mushrooms and taking a mushroom extract to support the immune system.

This originally appeared as “Eat Well” in “6 Ways to Boost Your Immune System” in the January/February 2021 issue of Experience Life.