The omega-3 fatty acids found in some types of fish — such as salmon, sardines, herring, and mackerel — enhance the functioning of immune cells, says Erin Palinski-Wade, RD, CDCES, of Sparta, New Jersey, the author of 2-Day Diabetes Diet and a consultant for Swisse Wellness.

Palinski-Wade adds that DHA, a type of omega-3, may increase the activity of white blood cells, which further strengthens immunity. That's backed up by a study that found this effect was not only significant but also fast — within a week of consumption, those researchers said.

The National Institutes of Health (NIH) notes that zinc — a mineral abundant in meats like oysters, poultry, seafood, beef, and lamb — works with the protein found in meat to strengthen the immune system. Certain types of immune cells, including white blood cells, can't function without zinc, according to a review published in September 2016 in the Archives of Biochemistry and Biophysics.

Whether you get your protein from lean meats or vegan or vegetarian foods such as tempeh or tofu, make sure you get some at every meal to keep your energy and your strength up, advises McKenzie Caldwell, MPH, RDN, of Charlotte, North Carolina. She notes that the recommended daily allowance (or minimum amount needed) for protein is 0.8 grams (g) per kilogram (kg) of body weight. (To convert to kg, divide weight in pounds by 2.2.) For example, a 150-pound person weighs about 68.2 kg, meaning they need about 54.5 g of protein each day.

For the most heart-healthy option, choose lean protein. According to the National Heart, Lung, and Blood Institute, lean protein has 55 calories and 2 to 3 g of fat per serving. Examples include 1 ounce (oz) of dark meat chicken with the skin removed, 1 oz of roast beef, and low-fat cheese that has a maximum of 3 g of fat per oz.

Plenty of vitamins and minerals play a role in immune function, but a particular standout is magnesium, according to an article published in 2017 in Molecular, Genetic, and Nutritional Aspects of Major and Trace Minerals. Your immune system is made up of numerous components, including proteins like antibodies, lymphocytes, and macrophages, which all work together to repel invaders, such as viruses. Palinski-Wade notes that magnesium plays an important role by improving how each of these protein types function.

Previous research has noted, for example, that magnesium helps lymphocytes bind to invaders so they can be removed from the body, and helps prevent antibodies from being impaired.

The Cleveland Clinic cites a breadth of foods with ample amounts of magnesium, from pumpkin seeds and spinach to avocados and brown rice.

Perhaps the sweetest surprise on that list? Dark chocolate at 70 to 85 percent cocoa comes in at about 65 milligrams (mg) of magnesium per ounce, notes the U.S. Department of Agriculture. That makes an ounce a good source of the nutrient. Just be sure to enjoy this treat in moderation, as that ounce has 170 calories.

Vitamin C may help protect the body against oxidative stress, and that helps support immune function, says Palinski-Wade. Oxidative stress happens when there is an imbalance of healthy antioxidants and harmful substances called free radicals in the body, research shows. Oxidative stress is associated with an increased risk of various health conditions, including stroke, cancer, and diabetes, a study suggests.

As a type of antioxidant, vitamin C is a free-radical scavenger and enhances immunity by supporting cellular function, among other benefits, notes an article published in September 2017 in Nutrients. 

Choose foods that are loaded with this vitamin. According to the NIH, foods with vitamin C include oranges, lemons, strawberries, blueberries, tomatoes, broccoli, leafy greens like kale, and bell peppers. To help retain vitamin C in your food, enjoy these foods in raw form when possible. Vitamin C is heat sensitive, so cooking can reduce the amount of this nutrient that your body can take in, according to an article published in April 2018 in Food Science and Biotechnology.

For a filling snack that's also a boon to your immune system, reach for a handful of nuts or seeds. Not only do they have magnesium, but they're rich in vitamin E, an antioxidant that's been shown to improve the body's ability to fight off bacteria and viruses, according to the NIH.

Plus, it doesn't take much to get the benefits, Caldwell notes.

"Just one Brazil nut packs more than 100 percent of your daily selenium needs, a mineral that can strengthen your immune system," she says. Indeed, according to the NIH, 1 oz of Brazil nuts (about six to eight nuts) provides 989 percent of the DV of selenium.

A study published in September 2018 in Nutrients noted that selenium plays a crucial role in immune response because the micronutrient helps regulate immune cell function and lowers inflammation.

Just a small handful of other options, such as sunflower seeds, almonds, walnuts, and pecans, can give you that vitamin E boost, and they're a tasty addition to salads and other dishes, says Caldwell. They're versatile, too, since you can roast them for a snack or make your own homemade nut flour, as the Healthy Maven describes in one of her recipes.

One caveat to keep in mind is that portion control is essential when it comes to nuts. They're a healthy food but are calorie dense, so overindulgence can contribute to weight gain, says Caldwell.

Garlic gets its distinctive smell from sulfur compounds, says Palinski-Wade, and whether or not you love the aroma, it offers protective benefits to your health and immune response, she says. That's because when garlic is crushed or chopped, it produces allicin, which previous research has highlighted for its antiviral and antibacterial properties.

Onions have a substance called quercetin, she adds, which may help regulate histamine response and contains antiviral properties, according to a study published in January 2016 in Viruses. 

Looking for a powerful immune-driven dinner? Whip up some fresh pasta sauce with garlic and onions, plus tomatoes for that vitamin C addition, she suggests. This recipe from Taste of Home can show you how.

"Yogurt is rich in probiotics, the good bacteria that support gut health," says Palinski-Wade. Johns Hopkins notes that a huge proportion of the immune system is actually in the gastrointestinal tract.

In a study published in May 2017 in Nutrients, participants without diabetes who ate yogurt with probiotics daily saw an increase in protective immune function compared with the control group. To avoid added sugar, choose plain, unsweetened yogurt.

Not a yogurt fan? Try other fermented foods instead. A study in the July 2023 issue of Cell details a clinical trial of 36 adults given two different diets, chosen because both have shown benefits for gut health, and researchers wanted to determine which would be most useful. The group who ate or drank fermented foods and drinks like yogurt, kimchi, kefir, and kombucha showed less inflammation compared with a group assigned to a high-fiber diet alone, and had more diversity in their digestive systems’ beneficial bacteria.

Other Tips to Boost Your Immune System

Let's say you load up on all this good stuff and still get socked with a virus. It happens. But continuing with healthy eating will shorten the duration of symptoms if you have a mild case of whatever you've caught, says Caldwell.

Keep Eating

"Most important is continuing to eat enough food overall," Caldwell notes. "We might not be able to totally prevent getting sick by eating well, but if you're not getting enough nutrients, and especially not enough protein, you're going to lack the energy to fight it off."

Skip the Added Sugar and Unhealthy Fats

Also, avoid added sugar when you can. Added sugar is packed into soda, juice, cakes, candy, and cookies, notes the American Heart Association. It can trigger inflammation in the body, research indicates, and when your system is fighting against that, your immune system may not have enough power to combat outside stressors such as pathogens and viruses, according to a past study in animals.

"In addition, high amounts of saturated fat and trans fat in the diet can increase inflammation in the same way, and that weakens the immune response," says Palinski-Wade. These are found in foods like fatty cuts of beef, poultry skin, baked goods, butter, and whole milk, says the USDA.

Drink More Water

“Stay hydrated” has become the mantra in everything from losing weight to boosting energy, and it does provide some magic for improving health overall, says Tiffany DeWitt, RD, a senior research scientist at healthcare company Abbott in Columbus, Ohio.

Proper hydration levels can help multiple bodily systems, including immunity, research shows. Also, Mayo Clinic notes, if you’re already on the cusp of a cold, water can loosen congestion.

Although many people may see juices — especially orange juice — as an effective hydration strategy, and good for the immune system, nutrition researchers caution that these are sugar bombs, and there's no proof that OJ prevents or shortens illness.

Your best bet is water, says DeWitt. Electrolytes from beverages like zero-sugar Gatorade can be helpful for allowing your body to absorb fluids better, she adds, but you can also get these through foods without artificial sweeteners, like bananas, avocados, Greek yogurt, nuts, kale, and spinach.

Enjoy Your Food

Whether you're feeling under the weather or not, eating mindfully can be helpful, simply because you'll slow down, feel less rushed, and truly enjoy your food, Caldwell says. Stress has been linked to poor immune function, in a study published in October 2015 in Current Opinion in Psychology, so see your meals as a chance to chill.

Healthy eating can boost your immunity, and it can lift your spirit and nourish your sense of well-being, too.