This winter could shape up to be a gnarly one if weather predictions play out, potentially ushering in a ghastly cold and flu season. It’s not just the plunging temperatures that leave us vulnerable to sickness, but a constellation of factors, including being indoors in dry air, which fosters germs and helps spread viruses, according to Keck Medicine of University of Southern California.

Getting a flu shot is critical in protecting your and (others’) health, but beyond that, you should also focus on building up your immune system. You can help do that by consuming healthy foods that tout immunity-boosting agents. “While there is no one miracle food that will miraculously cure a cold or ward off cancer, there are foods that you can eat every day to keep yourself healthy and ready to fight off any infections that may come your way,” says Catherine Brennan, RD. Here’s what registered dietitians recommend:

Beans

“Usually associated with their high-fiber content, this is also what makes [beans] good prebiotic foods. Prebiotics feed the good bacteria in the gut, and the gut is actually where most of the immune function in the body is mediated,” says Dr. Keith Ayoob, RD, nutritionist and associate clinical professor at the Albert Einstein College of Medicine. “Good for the gut, means good for immune function. Any beans are fine, so have the ones you like, including the kind in the can. Aim for half a cup three times a week. This amount has also been shown to reduce bad cholesterol 5-8 percent.

Berries

“Berries are packed with antioxidants — key for our immune health because they help the body deal with inflammation or invaders, such as bacteria and viruses,” says Ashley Reaver, RD. “They are also high in soluble fiber and lower in sugar than other fruits, which can help keep inflammation at bay.”

Bison

“Buffalo meat is high in zinc, which is important in increasing white blood cells to fight off infections,” says Kerry Clifford, RD and spokesperson at Fresh Thyme Farmers Market, adding that bison is “packed with protein, iron and Vitamin B12, too.”

Oysters and shellfish

Speaking of zinc, oysters have more of the mineral than any other food, providing 493 percent of the daily requirement, says Samantha Cassetty, RD, NBC News BETTER's nutrition columnist. Cassetty adds that since most of us don't eat oysters every day (if ever), you can also get zinc from other seafood, like shrimp or crab.

Dark chocolate and cocoa powder

“Dark chocolate is high in antioxidants — flavonoids in particular,” says Reaver. “Like other antioxidants, flavonoids help to reduce the impacts of inflammation, which can tax the immune system.” Cocoa is rich in theobromine, notes Dr. Ayoo, which may help quell persistent coughs. “Cocoa powder is my recommended source. I recommend making your own hot chocolate with real cocoa powder (sweeten with some stevia or any preferred sweetener, but go easy on sugar).”

Citrus fruits

“Citrus fruits have long been thought to be immune boosters since they contain vitamin C, a powerful antioxidant,” says Brennan. “Although there is no evidence that vitamin C helps to prevent colds, it may actually help shorten the duration of a cold.”

Cruciferous vegetables

“Cruciferous vegetables such as kale, cabbage, brussels sprouts and cauliflower contain powerful phytochemicals in addition to fiber, vitamins and minerals,” says Brennan. “Studies have shown that consuming these vegetables may stimulate the immune system and reduce oxidative stress.”

Garlic

“Garlic is an anti-inflammatory and anti-bacterial,” says Dr. Divya L. Selvakumar, RD, nutrition specialist and nutrition professor. “It can help to reduce hardening of arteries (atherosclerosis) and lower blood pressure, boosting immunity and reducing heart disease and other bacterial inflammation.”

Whole grain bread

Cassetty points to a recent study comparing the impact of a whole grain-heavy diet to a refined grain one found that whole grains improved measures of immune function. The diets weren't designed to produce weight loss, and they were matched to provide the same amount of fruits and veggies. The only difference was the type of grain (which also impacts fiber levels). "The cool thing is the experiment included really easy swaps, like whole grain bread crumbs in place of ordinary breadcrumbs in a turkey meatloaf, which shows that even little changes make a difference," says Cassetty.

Green tea

“Green tea contains polyphenols, namely catechins, which may stimulate the production and activity of specific cells associated with combating viruses,” says Brennan. “In fact, studies have linked drinking green tea to many a whole host of health benefits. Look for brands without added sugar or artificial flavorings.”

Greek yogurt

Studies suggest people who consume a diet low in vitamin D are more susceptible to colds and the flu.

“Greek yogurt contains high levels of probiotics which may ease the severity of colds and keep the gut microbiome healthy and ready to fight off infection,” says Rebecca Shenkman, RD, expert in nutrition and director of the MacDonald Center for Obesity Prevention and Education at the M. Louise Fitzpatrick College of Nursing at Villanova University. “In addition, yogurt varieties with added vitamin D are an even better choice as studies suggest people who consume a diet low in vitamin D are more susceptible to colds and the flu. Check labels to make sure you choose yogurt products that are low in sugar, high in probiotics and have added vitamin D.”

Mushrooms

“Mushrooms contain the powerful compound of beta-glucans that help the natural killer cells of the body,” says Jackie Arnett Elnahar, a registered dietitian and CEO of TelaDietitian. “In a 2011 study, participants that ate one 4-ounce serving of cooked shiitake mushrooms for four weeks had better functioning gamma delta T cells and reductions in inflammatory proteins. Our immune system benefits from the evolution of the mushroom, which have developed a more advanced immune system than ours. In fact, powerful antibiotics such as penicillin and tetracycline come from fungi extracts”.