6 Eating Habits and Foods that Weaken Your Immune System

Because right now, you need to keep your defenses strong.

Keeping your immune system strong is one of the most important and impactful things you can do right now, as the coronavirus pandemic continues. But bolstering immunity is a two-sided coin: it's about choosing foods that help support immune function, while sidestepping behaviors that can weaken immunity. Here are six habits to be mindful of as you work on boosting your body's defenses.

Drinking too much alcohol

A glass of wine here and there can be a healthy way to get through this crisis. But excessive alcohol consumption, even short-term, can alter your immune system in ways that are particularly important right now.

In a paper published in the journal Alcohol Research, researchers note that there's been a long-observed relationship between excessive alcohol intake and a weakened immune response. The effect includes an increased susceptibility to pneumonia, and a greater likelihood of developing acute respiratory stress syndromes (ARDS)—factors that could potentially impact COVID-19 outcomes. Other outcomes observed involve an increased risk of sepsis, a higher incidence of postoperative complications, poor wound healing, and a slower and less complete recovery from infections.

Excessive drinking includes both binge drinking and heavy drinking. The Centers for Disease Control (CDC) defines binge drinking as four or more drinks during a single occasion for women, and five or more for men. Heavy drinking means consuming eight or more drinks per week for women and 15 or more for men.

If you find yourself drinking too much, cut back to a moderate amount of no more than one drink per day for women or two for men. And if you think you may need help regarding alcohol, there are several ways to seek professional services from home, including counseling via the Substance Abuse and Mental Health Services Administration national helpline: 1-800-662-HELP.

Going overboard with salt

You may associate excess sodium with problems like fluid retention and high blood pressure. But a new study from the University Hospital of Bonn conducted in both humans and mice concludes that too much salt may lead to immune deficiencies. Researchers found that when the kidneys excrete excess sodium, a domino effect occurs that reduces the body's ability to fight bacterial infections.

While COVID-19 is a viral illness, it can lead to secondary bacterial infections. And this emerging research may result in a better understanding of the relationship between excess sodium and overall immune function. According to the Dietary Guidelines for Americans, the advised daily cap for sodium is under 2,300 mg per day for healthy adults, less than the actual average intake of 3,440 mg per day.

According to the CDC, more than 70% of Americans' sodium consumption comes from processed foods. That's why the best way to curb your intake is to limit highly processed products, like canned soup and frozen pizza. Check the mg of sodium per serving on Nutrition Facts labels.

As for salting your food, one teaspoon of table salt contains 2,300 mg of sodium. If you use salt sparingly to season fresh food, you can still remain under the recommended cap. For example, a quarter teaspoon of salt, which is a generous amount if you measure it, provides 575 mg of sodium. Combining salt with other seasonings, like herbs and spices, can also help reduce the need to over sprinkle.

Consuming excess sugar

Cutting back on excess added sugar is a smart idea for a number of reasons, including good mental health. It's also beneficial for immune support.

A study published in The American Journal of Clinical Nutrition found that after an overnight fast, humans fed 100 grams of sugar experienced a reduction in the ability of immune cells to engulf bacteria. The greatest effects were found between one and two hours later, but lingered for up to five hours.

This doesn't mean you have to nix sugar completely, but avoiding an ongoing surplus or short-term overindulgence is a worthwhile goal. The American Heart Association recommends limiting added sugar—the kind added to foods by you or a manufacturer—to no more than six teaspoons worth per day for women, and nine for men. One teaspoon equals four grams of added sugar, so that's 24 and 36 grams of added sugar respectively for women and men daily.

If you're prone to stress-eating sugary goodies, test out some alternative coping mechanisms. Reaching out to loved ones, practicing meditation, engaging in an indoor workout, or even playing a video game may reduce the need to eat your feelings.

Overdoing caffeine intake

Coffee and tea are health-protective, due to their high levels of antioxidants linked to anti-inflammation. However, too much caffeine can interfere with sleep, and that result can increase inflammation and compromise immunity.

To best support immune function, ditch caffeinated drinks with no nutrients made with sugar or artificial sweeteners, like soda and energy drinks. When you do enjoy coffee and tea, be sure to cut off your caffeine intake at least six hours before bedtime to prevent sleep interference.

Skimping on fiber

Fiber supports good digestive health and helps to shift the makeup of gut bacteria in ways that enhance both immunity and mood. Research shows that a higher intake of dietary fiber and prebiotics supports healthier immune function, including protection against viruses. Adequate fiber also promotes more and better sleep. Yet just 5% of Americans consume the recommended daily goal of at least 25 grams per day for women and 38 grams for men.

The best way to upgrade your fiber intake is to eat more whole foods, including vegetables, fruit, whole grains, pulses (beans, lentils, peas, chickpeas) nuts, and seeds. Trade lower-fiber processed foods for fiber-rich unprocessed fare. Swap sugary cereal for oatmeal topped with fruit and nuts, exchange white rice for brown or wild. Replace fiberless meat with beans or lentils, traditional pasta for pulse pasta, and exchange packaged snacks, like cookies and chips, with combos of fruit and nuts or veggies with hummus or guacamole.

Not eating enough green veggies

Aiming for seven cups of a wide array of produce daily provides numerous health benefits, but green veggies may be particularly helpful for immunity. These plants provide key nutrients known to help immune function, including vitamins A and C, plus folate. Greens also offer bioactive compounds that release a chemical signal that optimizes immunity in the gut, the location of 70-80% of immune cells.

For the most benefit, zero in specifically on green veggies in the cruciferous family, which include kale, collards, broccoli, bok choy, cabbage, and Brussels sprouts. Incorporate at least three cups per week—either raw, like kale salad, vinegary slaw, and fresh broccoli florets with dip, or steamed, sautéed, oven roasted, and stir-fried versions.

Cynthia Sass, MPH, RD, is Health's contributing nutrition editor, a New York Times best-selling author, and a private practice performance nutritionist who has consulted for five professional sports teams.

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