2020 was a heck of a year—one that reminded us just how important a good immune system is. Dr. William Li, author of Eat to Beat Disease, is no stranger to the topic. He shares the key things you can do right now to boost your body’s main defense system.

colorful illustration of woman
Illustration by Asia Pietrzyk
| Credit: Illustration by Asia Pietrzyk
illustration of Dr. William Li
Credit: Illustration by Alessandra Olanow

If there's ever been a good time to focus on your health, it's now. And if there's ever been a good person to tell you how to do that, it's Dr. William Li, a Harvard-trained physician who literally wrote the book on boosting immunity with food (the New York Times bestselling Eat to Beat Disease). "When our immunity is strong, our health is strong," Li says. "When it's weak, we become vulnerable to disease. With winter flu season, and the pandemic still a threat, keeping your immune system in top shape is one of the most important things you can do." This is easier than it sounds, says Li, because a host of factors affect the body's defense systems: "It's not about doing one thing perfectly; it's about doing a lot of small things as best you can."

First, focus on what you put into your body, making sure it's good for your microbiome (the healthy bacteria that live in your digestive system). "The gut is a command center for our immunity," Li says. "If you build your meals around vegetables, legumes, fibrous foods, and whole grains, all of which support good bacteria in your gut, you'll be ahead of the game when it comes to immunity."

Next, think about what your body is doing: namely moving, sleeping, and stressing. "Exercise stimulates your stem cells, which replenish your immune system," the doc says. "When you sleep, your immune system updates its operating system and reboots itself." Stress does the opposite. "The stress hormone cortisol reduces the number of immune cells in our bloodstream," Li says, which is why you're more susceptible to infection when you're tired. Focus on getting 30 minutes of exercise per day and seven to eight hours of sleep per night, and find healthy ways to manage stress. "For me, taking a pause, reminding myself of what really matters, and letting go of what doesn't helps me re-center and limit stress," he says.

illustration of bandaid on arm
Credit: Illustration by Asia Pietrzyk

And a side effect of eating well, exercising daily, and getting enough sleep is lowered stress levels. Adjust your habits accordingly and you'll be on the right track.

Finally, remember the health habits you learned as a kid. "The pandemic has reminded us how important proper handwashing is (with soap, not just a rinse of water!), but it's also a good reminder for general hygiene," Li says. Brush your teeth and floss daily to improve your mouth's microbiome, which helps ward off illness. Get regular preventive health checkups at the doctor. And always get the flu shot! "It has always been important," Li says, "but this year, it's more critical than ever."

A Few Swap-ins To Make You Strong

Mushrooms, Not Processed Meats

'Shrooms have a meaty texture and natural immune-boosting power that make them a mighty meat alternative.

Yogurt, Not Cream

Trade sour cream, butter, and heavy cream for yogurt to add a probiotic kick to foods that want some creaminess.

Kimchi, Not Raw Vegetables

OK, this isn't really an either/or—veggies are great. But fermented foods like kimchi are extra good for your gut (and food's flavor!).

This article originally appeared in our Winter/Spring 2021 issue. Get the magazine here