Last year’s ferocious flu season was a good reminder of the importance of a strong immune system. The better our immune health, the more likely we are to fend off colds, flu, and other infections.
“Our immune system is a network of cells, organs, and chemical messengers that work together to protect us from foreign invaders and pathogens and to heal damaged tissues,” says Robin Berzin, MD, CEO and founder of Parsley Health. And one of the best ways to boost immunity is through what we eat — and what we don’t eat.
“Foods can either boost immunity or inhibit immunity,” agrees Vincent Pedre, MD, an internist in private practice in New York City and the author of Happy Gut.
How does food affect the immune system? First, the immune system needs key nutrients to function optimally. Second, the bacterial community in the gut— which has a powerful influence on immune function — is shaped by what you eat. Third, immunity can be negatively affected by leaky gut syndrome, which is often triggered by food allergens. Finally, some foods directly attack white blood cells (key immune-system cells), preventing them from doing their job.
So which foods boost immunity and which ones sabotage it? Here’s a list of immune-boosting superstar foods — and some immune-wrecking foods — from Berzin and Pedre.
Mushrooms. Shiitake, maitake, and reishi mushrooms all have powerful immune-enhancing effects, says Pedre, thanks to potent molecules called beta-glucans. “B1-3-d-glucans and B1-6-d-glucans help boost the immune response by activating white blood cells and increasing the number of Th1 lymphocytes [a type of white blood cell],” he explains. “They also help find and eliminate cancer cells in the body.” Matsutake mushrooms are high in vitamin D, an essential component of any immune-boosting regimen.
Salmon and sardines. Like matsutake mushrooms, salmon and sardines are high in vitamin D — and studies have shown that vitamin-D deficiency is associated with increased autoimmunity, as well as susceptibility to infection. Berzin and Pedre both recommend these fatty fish for immune health. Sardines, in particular, are an excellent choice because of their small size; the smaller the fish, the fewer toxins they generally have.
In addition to being high in vitamin D, salmon has one of the best ratios of omega-3 fats to mercury of any available seafood. (For more on choosing healthy seafood, see “How to Choose Seafood That’s Nutritious, Sustainable — and Safe.”)
Fermented foods. Berzin recommends fermented foods like kombucha, kimchi, and sauerkraut because they’re rich in live cultures and increase the healthy bugs in your gut — and the healthier your gut’s bacterial community, the more robust your immune function.
Dark leafy greens. Greens are full of micronutrients, minerals, and antioxidants, all of which your body needs to have an optimal white-blood-cell force, says Pedre. But, he cautions, try to buy organic produce, because “pesticides attack our body’s ability to mount an appropriate immune response.”
Bone broth. Your grandma was right: When you get a cold, eat chicken soup. But, says Berzin, the quality of your soup matters. “Bone broth made in the traditional way of boiling bones for 24 to 48 hours strengthens the gut lining and reduces inflammation,” says Berzin. So, skip the canned soup and try to make or find high-quality chicken soup.
Sugar. Sugar is Immune System Enemy No. 1. “We know that sugar stuns white blood cells for up to six hours, so they cannot do their job,” says Pedre. “The same is true regardless of how you get your sugar — sugarcane, processed carbs, white starches (such as bread, rice, and pasta).” So if immune boosting is high on your list of goals, steer clear of the sweet stuff.
Gluten. Studies show that gluten loosens the tight junctions of the gut lining in everyone. So even if you can eat gluten without noticeable symptoms, your gut is working double time to process this problem-causing protein — and energy is being diverted away from supporting and sustaining a healthy immune system.
Other top food allergens.The most common allergenic foods are wheat/gluten, dairy, soy, corn, peanuts, and eggs, which can all contribute to leaky gut and subsequently undermine immune function. If you’re plagued by poor immune function, consider doing an elimination diet to see if one of these foods is a trigger for you. (For more on eliminating trigger foods, see How to Heal a Leaky Gut.)