Everyone’s always saying what an amazingly efficient immune system we have, but if that’s true, why do we catch colds in the winter or suffer from allergies in the spring? The answer lies in ourselves. We don’t keep our immune system in fighting shape. Instead, we do all sorts of things that make it weak in the knees. We smoke, drink alcohol, burn ourselves out with stress, and eat diets filled with immune-system saboteurs.
Nutritionists agree that what we eat plays a big role in fighting off germs. “Our immune system is like a finely honed, intricately choreographed dance,” says Beth Reardon, RD, an integrative nutritionist at Duke Integrative Medicine, North Carolina. Every cell has a specific role, she says, and requires key nutrients to survive and work properly. That’s why the standard American diet—desperately lacking in important nutrients—puts the immune system at risk. The best way to maintain a healthy body? You got it: Eat well.
Nine power foods can help you boost your immune system.
Known as one of nature’s more potent remedies, garlic has “antiviral, antifungal, and antibacterial properties,” says Christine Gerbstadt, MD, RD, a physician and nutritionist in Sarasota, Florida. And for those who think medicine should smell bad, its effectiveness may be linked to allicin, the sulfurous chemical compound responsible for crushed garlic’s unmistakable, pungent odor. Gerbstadt says studies show that allicin not only inhibits the growth of bacteria, it can even kill some germs on contact. In one study at Boston City Hospital, garlic successfully killed 14 strains of bacteria taken from the noses and throats of children with ear infections. Now for the tricky part: To experience the full benefits of garlic in combating colds and flu, you’d have to eat an entire bulb—raw—every day. However, softening garlic by roasting or sautéing will subdue the strong flavor and lend a more palatable sweetness while still retaining most of its immune-boosting potency. What’s more, eating any amount of garlic will provide some benefit, says Gerbstadt.
>> Shiitake mushrooms
Long revered in China for both culinary and medicinal reasons, shiitake mushrooms add more than their rich flavor to a dish. Research shows that shiitake help produce a type of white blood cell called natural killer cells, which release a type of protein into the infected cells that causes them to self-destruct. Research also attributes the powerful effect of shiitake mushrooms to their unique complex sugars—called lentinan. Structurally similar to bacteria, lentinan “tricks” your body into feeling threatened, which kicks the immune system into a higher gear.
This comforting beverage does an admirable job of soothing the throat and relaxing the senses, even as it helps build up your resistance behind the scenes. Green tea, one of the least processed varieties, contains the highest amount of nutrients, but black teas are also rich in health benefits. In fact, powerful compounds known as polyphenols comprise nearly 30 percent of their dry weight. Why is that so important? Well, thanks to the air we breathe and much of the food we eat, our body is constantly bombarded with free radicals, which steal electrons from healthy cells and, in the process, damage their DNA. The selfless polyphenols offer up their own electrons to these unstable atoms, rendering them harmless and eliminating the threat, explains Kerry Neville, RD, a dietitian in Kirkland, Washington.
This breakfast staple offers much more than a sunny start to the day: Just one orange provides more than 100 percent of the daily value for vitamin C, a powerful antioxidant that helps strengthen the immune system. While there’s conflicting evidence about vitamin C’s cold-prevention power, most nutritionists and doctors agree that it certainly can’t hurt. One way vitamin C helps boost immunity is by stimulating the growth of antibodies that fight off infections, says Lona Sandon, RD, associate professor at the University of Texas Southwestern. Vitamin C is part of the chemical reactions that allow the body to synthesize proteins needed for antibodies. The more vitamin C that’s available to the body, the faster antibodies can be made. Studies show vitamin C also acts as an antihistamine, lowering blood levels of defensive chemicals (histamines) released by the immune system that actually exacerbate stuffiness and congestion. Finally, vitamin C helps produce prostaglandin E1 in the body, an anti-inflammatory hormone. While inflammation is a natural bodily response signifying something is physically not right, Sandon says, chronic, low-grade inflammation—which many of us suffer from—can actually cause the immune system to constantly fight the inflammation. And if the immune system is busy doing that, there’s a good chance it’ll miss the beginnings of another illness.
Delectable proof that big things can come in small packages, blueberries get a lot of votes as the ultimate immunity food. A powerhouse of antioxidant phytonutrients—health-promoting components found in plants—blueberries are also a good source of both vitamins C and E. “When vitamins C and E work together, they produce their most potent antioxidant effects,” says Reardon. While vitamin C, the body’s No. 1 water-soluble antioxidant, patrols the body’s waters, fat-soluble vitamin E works to protect fatty tissues from free radicals.
>> Sweet potatoes
Rich in carotene, the chemical that gives certain vegetables their orange color, sweet potatoes are a key player in the fight against infection. The reason? The liver converts carotene to vitamin A, and according to Mary Ellen Camire, PhD, a professor in the Department of Food Science and Nutrition at the University of Maine, “Vitamin A fortifies your first defender—your skin—by making it less permeable to germs.” Sweet potatoes also contain about 27 percent of the recommended daily value of vitamin C, and recent research has shown that the unique proteins in sweet potatoes may have antioxidant effects.
>> Lean beef
Beef gets a bad rap sometimes, primarily because most Americans eat too much of it. But the rich zinc content of lean, organic beef can bolster the immune system—just one 4-ounce serving provides approximately 42 percent of the recommended daily value. Zinc figures prominently in the production of white blood cells, says Camire. Too little zinc leads to a drop in them, which increases your risk of infection. Unlike other types of cells, most immune cells live only a short time and cannot divide or reproduce on their own. Because zinc spurs rapid cell division, it helps replace and repair these important members of the immune team. Looking for a vegetarian source of zinc? A quarter cup of pumpkinseeds packs approximately 17 percent of the RDA.
Loaded with nutrients and essential vitamins, spinach also contains folate, important when it comes to the production of new cells. Neville explains that in addition to being short-lived, immune cells get produced in fairly low numbers. When the body is threatened, one division of the immune system jump-starts production of cells targeted for the specific invaders. And the immune system depends on folate to increase the supply of cells. But that’s not all: Researchers have identified at least 13 different compounds in spinach that act as antioxidants. One of these is quercetin, a phytochemical that has been shown to help prevent many viruses from multiplying. Neville recommends adults include approximately three cups of spinach in their diet each week.
The “good” bacteria in yogurt—known as probiotics—make an essential contribution to a healthy immune system. The stomach and intestinal tract contain more than 500 different varieties of bacteria, and probiotics help maintain a balance between the good and bad bacteria by crowding out pathogens and preventing them from attaching to gut walls. Probiotics also feed on nondigestible fibers called prebiotics, producing short-chain fatty acids that decrease acidity in the colon. The decreased acidity makes the colon uninhabitable for most infection-causing pathogens, which, in turn, allows for increased mineral absorption. Research suggests that probiotics can also enhance the body’s immune response by increasing levels of key players, says Reardon, including natural killer cells. Studies from the University of California have shown that yogurt specifically helps the body build a protein called gamma interferon, which aids the body in developing white blood cells.
By Wendy McMillan