The best and worst foods for your immune system

What to eat and what to avoid to help boost your immunity.
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A healthy diet won’t prevent the coronavirus, but it can help strengthen your immune system.Alexandra Grablewski / Getty Images

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By Samantha Cassetty, RD

As the highly contagious coronavirus continues to run its course, the question on everyone’s mind is how to stay infection-free. There are the Centers for Disease Control basics, but eating well (or not) makes a difference, too. A healthy diet won’t prevent the coronavirus, but it can help strengthen your immune system — and a less healthy diet can undermine it.

Fueling your immune system

Your immune system is like an army with very sophisticated weapons in the form of cells and other compounds. For this army to function optimally, it needs a steady stream of supplies, which you get through your diet.

The best diet for your immune system is a minimally-processed, mostly plant-based diet — one that's about 75% plant foods. Keep in mind that you’re also better off getting the nutrients you need from your plate rather than a pill bottle, though select supplements may be useful in some cases, such as to ensure you get the necessary amount of vitamin D, a nutrient that’s only found in a limited number of foods.

Here’s how to eat to support your immune system.

Focus on fruits and vegetables

Various building blocks for your immune system’s machinery come from fruits and vegetables. Some of the key immune-strengthening nutrients in these foods include vitamin C, beta carotene (the precursor to vitamin A) and certain B vitamins, like folate. Many fruits and veggies also supply polyphenols, antioxidants that get broken down into food and contribute to healthy gut bacteria. These compounds, which are also found in other plant foods (like extra virgin olive oil, whole grains, pulses, tea and coffee) help your beneficial bacteria flourish. They also help optimize your gut environment, which is where up to 80% of your immune cells are located.

Polyphenols work their immune-enhancing benefits in other ways too. For example, they calibrate pro- and anti-inflammatory cytokines. In severe cases of COVID-19, the pro-inflammatory cytokines take over and may be responsible for causing death in some instances.

Fruits and vegetables are some of the best foods for the immune system. When choosing fruits and veggies, seek out a variety of options. Go for fresh, frozen, dried and canned fruits and veggies of all colors. Don’t forget that juices like 100% OJ, pomegranate juice and vegetable juice can also help you reach your fruit and veggie goals, which for most people is a minimum of two cups of fruit and two and half cups of veggies each day.

Prioritize whole grains

Whole grains (including oats, quinoa, brown rice and whole wheat) do their part by supplying nutrients like folate, magnesium, selenium and iron to your immune system. A study published in BMJ Gut suggests that whole grains can help regulate inflammation, which contributes to the development of a multitude of diseases, including type 2 diabetes. The same study showed that eating whole grains instead of refined grains led to weight loss among overweight people. The authors suggested this swap may be a helpful strategy for reaching a healthier weight. Since we know that COVID-19 produces more serious illness among those with type 2 diabetes and those who are severely obese (with a BMI over 40), swapping refined pasta, bread, crackers, cereal and rice for a whole grain version is an easy — and smart — upgrade.

Eat mostly healthy fats

All types of nuts and seeds (plus their butters), avocados and olives (and their oils) and oily fish (such as salmon and sardines) help regulate your body’s inflammatory process. Depending on the specific food, it may also supply key nutrients (such as selenium, vitamin E, zinc, iron or magnesium) that are involved in optimal immune cell functioning. Use these foods to help punch up your meal. For example, saute veggies in extra virgin olive oil and top with some chopped nuts or hemp seeds.

Choose plant-based proteins

Pulses, which include beans, legumes and dried peas, are whole food and shelf-stable forms of plant-based proteins that supply immune-optimizing nutrients, including fiber, magnesium and iron. Whether you’re actively trying to cut back on meat or just trying to stretch your meat (and food budget) further, these foods will help. Other whole food forms of plant-based protein include tofu and edamame.

If you’re new to these foods, try serving them in familiar ways. For example, make a black bean quesadilla, toss shelled edamame into a favorite stir-fry, or use hummus (a chickpea puree) as a sandwich spread. Though there’s nothing wrong with the convenience of fake meat products (like the Beyond Burger), these foods are heavily processed, so it’s generally better to choose whole-food forms of plant-based proteins instead.

Eat seafood twice a week

The US Dietary Guidelines recommend eating seafood twice a week and this advice can help your immune health too. Seafood supplies anti-inflammatory omega-3 fatty acids and other nutrients, including magnesium and zinc, that help support your immune system. Plus, when you replace red meat, which is high in pro-inflammatory saturated fats, with seafood you can help keep chronic inflammation in check.

Enjoy fermented foods

Yogurt, sauerkraut, kombucha and kimchi are examples of fermented foods that supply beneficial bacteria to your gut. According to one review, supplementing with probiotics, such as the ones found in fermented foods, helped prevent upper respiratory infections and shaved about two days off of the recovery period among the people who did get sick compared with those who took a placebo (a fake treatment).

Watch out for the worst foods for your immune system

To keep your immune system strong, it’s also a good idea to limit these foods, which all play a role in weakening your defenses.

Added sugars

Whether from desserts, sugary drinks or sneakier sources like plant-based milks, whole grain cereals or yogurts, a high-sugar diet may tamp down your immune response.

Excessive alcohol

Too much alcohol can weaken your immune system. It has also been linked with a higher chance of respiratory infections. Stick to a drink (for women) or two (for men) a day.

Heavily processed foods

The majority of sodium in your diet comes from these foods and research suggests that excess salt might undermine your immune system’s ability to cope with an invader. Heavily processed foods are also made with refined grains, which alter your metabolic response and can ultimately leave you more susceptible to serious infections. Some major culprits include fast food meals, pizza and chips.