EATING FOR RESISTANCE
Aco-worker sneezes and a cloud of viruses fills the air. Pick up a pen or a pair of socks, and you’re exposed to thousands, possibly millions, of bacteria. Walk barefoot across a lawn, and you’re picking up fungi, parasites, and still more bacteria. A dangerous world? It would be if you didn’t have your immune system to protect you.
“Our bodies are constantly bombarded with bacteria, viruses, and other organisms trying to gain entry,” says Thomas Petro, PhD, associate professor of microbiology and immunology at the University of Nebraska Medical Center in Lincoln. “The immune system is the one defense we have against this takeover.”
It’s truly a battle for survival. A mere inch of freshly washed skin may be home to more than 1 million bacteria. Without strong immunity, microbes in and on our bodies would quickly multiply to unimaginable numbers. Yet every minute of every day, our immune systems keep these microscopic invaders in check.
To a large extent, your ability to maintain a healthy immune system depends on what you eat, says Dr. Petro. Research has shown, for example, that in parts of the world where healthy, nutritious foods are in short supply, people frequently have weak immune systems, and as a result, they are much more prone to developing infections. Similarly, in people with serious illnesses such as cancer, who often have trouble eating well, immunity can take a downturn.
Having a low level of even a single nutrient may cause the immune system to pay the price. In a review done at the University of Southampton in England, researchers looked at nutrients that play a key role in immune system function and found that the essential amino acids, the essential fatty acid linoleic acid, vitamin A, folate, vitamin B6, vitamin B12, vitamin C, vitamin E, zinc, iron, copper, and selenium are all required for healthy immune system function. The researchers also found that almost all aspects of immune system health are affected by deficiencies in these nutrients and that increasing intakes of them can enhance immune system function.
And in a small study done at the department of nutrition and food management at Oregon State University, researchers looked at the relationship between an increased intake of vitamin B6 and white blood cell counts in seven young women over 3 weeks. When the women increased their intakes of vitamin B6 from 1.5 milligrams to 2.1 milligrams, they experienced a 35 percent increase in white blood cell counts.
And what you do eat may wreak as much havoc on your immune system as what you don’t eat. Junk food and processed foods take a real toll on your immune system, says Mary Jo DiMilia, MD, an integrated medicine physician at Mount Sinai Medical Center in New York City.
“Food is powerful medicine,” says Keith Block, MD, medical director of the Block Center for Integrative Cancer Care in Evanston, Illinois. In fact, eating more of certain foods and less of others can substantially boost the body’s ability to fight most illnesses, from colds to cancer.
Even though people talk about the immune system, it actually consists of two very different parts. One part of the immune system is nonspecific. That is, it attacks—or simply resists—just about everything it comes into contact with. It’s like a first line of defense. Your skin, for example, provides a physical barrier against bacteria, viruses, and other invaders. It also secretes sweat and oil, which, because they are acidic, help block the growth of harmful bacteria. Your stomach secretes germkilling acids and enzymes. Your saliva and tears contain an enzyme that destroys bacteria. Even the hairs in your nose keep germs from entering your body.
Should a microbe be lucky enough to breach the nonspecific part of the immune system, it’s met by the next level of defense—the specific system. This second part of the immune system is extremely selective. Depending on the type of invader it encounters, it launches customized weapons called antibodies, which are proteins specifically designed to kill one particular invader and no other.
The immune system is capable of making more than 100 billion types of antibodies, so it can attack just about anything it comes into contact with. What’s more, these antibodies have a long memory. Once you’ve been exposed to a germ, the immune system will remember it. If that same germ comes back—months, years, or even decades later—the appropriate antibodies will quickly kill it before it can make you sick.
The most powerful protection that you can give your immune system is to eat a well-balanced diet containing a variety of fruits, vegetables, whole grains, seeds and nuts, and seafood, says Dr. DiMilia. These foods are high in nutrients that can help keep your immune system healthy. What’s more, some of these nutrients are antioxidants, which may help give the immune system an added boost.
Here’s why antioxidants are so important. Every second, immune cells in your body are hit by a barrage of free radicals, harmful oxygen molecules that are created in enormous numbers every day. Since free radicals are missing an electron, they rush through your body, stealing electrons wherever they can find them. And every time they grab an electron, another cell is damaged.
The antioxidants in such foods as brightly colored fruits and vegetables, however, literally come between free radicals and healthy immune cells, offering up their own electrons. This neutralizes the free radicals, stopping them from doing further harm. In the process, your body’s immune cells stay protected and strong.
“When your immune system is going to fight something, it fights it by oxidizing it,” says Shawn Talbott, PhD, a nutritional biochemist and author of The Health Professional’s Guide to Dietary Supplements. “So your immune system will actually give a virus or bacteria a blast of oxidation to try to kill it. Therefore, if you are fighting off a lot of these viruses or bacteria, you will have a lot of oxidation happening in your body and will need more antioxidants,” he says.
In a study at Memorial University of Newfoundland in Canada, researchers found that people who got the most of a variety of nutrients, including antioxidants such as beta-carotene and vitamins C and E, in their diets were able to produce greater numbers of natural killer cells—immune cells that search out and destroy bacteria and other invaders—than folks getting the least. Another study found that people who got large amounts of a variety of antioxidants typically got sick about 23 days a year, while those getting smaller amounts got sick about 48 days a year.
Even though vitamin C is a powerful antioxidant, it helps the immune system in yet another way. The body uses vitamin C to make interferon, a protein that helps destroy viruses in the body. Plus, vitamin C may increase levels of a compound called glutathione, which has also been shown to keep the immune system strong.
In one large study, researchers at the University of Helsinki in Finland reviewed 21 smaller studies that looked at how well vitamin C was able to beat colds. They found that people getting 1,000 milligrams of vitamin C a day were able to shorten the duration of their illnesses and reduce their symptoms by 23 percent.
And a more recent Swiss review of numerous studies revealed that 1 gram of vitamin C was effective in shortening the duration of respiratory infections including the common cold.
The Daily Value (DV) for vitamin C is 60 milligrams, but many researchers say that 200 milligrams is probably the minimum amount you need to maximize immunity. It’s easy to get this much vitamin C in your diet, Dr. Block adds. Half a cantaloupe, for example, has 113 milligrams of vitamin C, almost twice the DV, while a half-cup of Brussels sprouts has 48 milligrams, or 80 percent of the DV. Of course, you can also get a lot of vitamin C in citrus fruits, broccoli, guava, strawberries, rutabagas, radishes, and rose hips tea.
Vitamin E has also gotten a lot of attention for its role in boosting immunity. The body uses vitamin E to produce a powerful immune protein called interleukin-2, which has been shown to tackle everything from bacteria and viruses to cancer cells. The DV for vitamin E is 30 IU, and good sources include dark green leafy vegetables, walnuts and pecans, wheat germ, peanut butter, and vegetable oils.
Probiotics are beneficial bacteria in your intestinal tract that can improve health. And pro biotics can also help improve immune system function. Pro biotics interact with a specific part of your small intestine called the pyrus patches, which directly signal your immune system to be vigilant.
“Some probiotic drink mixes out there contain beneficial probiotic organisms,” says Patricia David, MD, MSPH, president of Healthy U in Columbus, Ohio. “And those are great if you’re on the go. But I encourage people to obtain their probiotics directly from food sources whenever possible—these food sources include yogurt, buttermilk, goat’s milk, coconut water, soy milk, miso, kim chi, and sauerkraut. For optimum probiotic exposure, look for yogurts and other probiotic products that contain bifidobacterium and/or lactobacilli.
Another way to increase your levels of beneficial immune-bolstering bacteria is to consume prebiotics—nondigestible food components that selectively stimulate the growth of “good” bacteria in the gastrointestinal tract, says Dr. David. “Natural sources of prebiotics include dandelion greens, spinach, kale, artichokes, legumes, onions, leeks, garlic, oatmeal, flaxseed, barley, and soy yogurt,” she says.
Just as eating the right foods can help keep the immune system strong, eating the wrong ones—specifically, those that are high in fat—can put it at a disadvantage. “A high-fat diet speeds up the aging of the immune system, although we don’t know why,” says Dr. Petro. “But we do know that it results in the production of more cell-damaging free radicals.”
Studies have shown that people who cut back on fat in their diets have a rapid increase in natural killer cell activity, a sign of immune system strength. In one study, researchers at the University of Massachusetts Medical School in Worcester put men on low-fat diets for 3 months. For every 1 percent the men were able to reduce the fat in their diets, the activity of their natural killer cells went up nearly 1 percent.
It isn’t necessary to go on an extremely low-fat diet to boost immunity, Dr. Petro adds. For most people, getting no more than 30 percent of calories from fat—and preferably getting between 20 and 25 percent—is probably ideal.
To cut fat from your diet, eat fewer processed foods, such as those that come in cans, packets, and boxes. With the exception of canned fruits, beans, and vegetables, many processed foods are often high in fat, not to mention salt and sugar. Eat more fresh fruits and vegetables, beans, and whole-grain breads and cereals. In addition, switching from full-fat dairy products to reduced-fat milk, yogurt, and cheese, and eating less red meat, will help bring your fat levels into the safety zone.