Why is it that some people hardly ever get sick? I wanted to learn their secrets. Some of these secrets, I discovered, are a bit unusual, but they have a basis in scientific fact…

BREWER’S YEAST

Barbara Pritzkat, age 84, hasn’t had a cold in decades. In 1983, at age 56, she started her second career as an archaeologist. She’s still surveying archaeological sites, most recently in the Syrian Desert, where temperatures can reach 110°F. She credits her good health to brewer’s yeast, which she takes in powder form dissolved in water every morning. She first learned about the health benefits of brewer’s yeast in the 1940s when she attended a lecture by Adelle Davis, a pioneering nutritionist.

The science: Most commercially available brewer’s yeast is extracted from the yeast that is used to ferment beer or wine. A single tablespoon contains the recommended daily allowance for most of the B vitamins, including folate.

Folate is one of the most important B vitamins because it breaks down and eliminates homocysteine, an amino acid, from the blood. Reducing homocysteine has been linked to a reduction in risk for stroke and heart disease. Folate also is thought to reduce the risk for a variety of cancers, including colon cancer.

Other B vitamins are needed for the maintenance of blood cells, nerves and the immune system. Brewer’s yeast also contains a variety of minerals, including chromium, a trace mineral that reduces blood sugar and improves glucose tolerance. In addition, a single two-ounce serving provides eight grams of protein, more than the amount in a large egg.

What to do: Take one to two tablespoons of brewer’s yeast daily. You can dissolve it in water or sprinkle it on your cereal or yogurt. Some people may suffer adverse gastrointestinal reactions at first. Start by taking a small amount and increase it gradually.

Any brand should be fine—even buying from bulk bins. But look for a kind that’s debittered—the taste is more palatable.

COLD SHOWERS

They’re not very pleasant, but your shivering body may thank you.

Nate Halsey, age 38, got hooked on cold-water hydrotherapy a decade ago, when one of his friends explained that cold showers were the reason that he never got sick. Nate, who had been getting sick fairly often, gave it a try—and hated it. He still hates it, but he likes the energy boost. He also appreciates that he never gets sick anymore.

The science: Researchers have found that cold-water submersion increases levels of disease-fighting white blood cells. In one study, scientists found that people who took cold showers daily for six months had fewer colds than those in a control group. In another study, year-round swimmers in Berlin, who took regular dips in freezing-cold water in the winter, suffered half as many chest infections as other people.

Exposure to cold water also may increase glutathione, one of the body’s main antioxidants—the study of Berlin swimmers found that they had elevated levels of glutathione.

What to do: Ease into it. Turn on the cold water for 30 seconds or so. With the shower running, stick your head in to wet your hair. Turn off the water, shampoo your hair, then turn the water back on to rinse off the lather and get your skin wet. Turn off the water again, soap your body, then turn the water back on to rinse off. The entire event should take about five minutes.

Caution: If you have a heart condition, Raynaud’s disease or blood pressure issues, talk to your doctor first.

GARLIC

Even people who do their best to take care of themselves aren’t immune to colds and flu. That was the experience of Susan Brown, age 51, a shiatsu massage therapist and former owner of a health-food store. She got the flu year after year—until her boyfriend recommended garlic.

Now she cooks with garlic every day, adding it to every dinner, which often consists primarily of vegetables and some kind of starch, such as rice or pasta. She also squeezes raw garlic on top of the dish. If she feels like she’s coming down with a cold, she eats garlic three times a day, and within 24 hours, she’s fine. She hasn’t gotten the flu since she started her garlic regimen more than six years ago.

The science: Garlic has antibacterial and antiviral properties. Researchers at the University of Western Australia found that people who began using garlic were able to reduce their sick days by more than 50%.

Some of the active ingredients in garlic inhibit the ability of platelets to form clots in the arteries—important for preventing heart disease and stroke. People who eat garlic regularly can have drops in blood pressure of about 10 mm Hg (millimeters of mercury).

What to do: Chew a clove of garlic whenever you feel a cold coming on or you want to give your health a quick boost. It’s best consumed raw, as cooking may destroy some of its health benefits. Most scientific studies are done with garlic supplements. However, some experts believe that the process of making the supplements destroys some of the health benefits.

Caution: If you’re on a blood thinner or have a bleeding disorder, such as hemophilia, talk to your doctor before consuming large amounts of garlic.

PROBIOTICS

Tony Japour, MD, age 51, is a molecular virologist and pharmaceutical researcher. His impressive credentials didn’t keep him healthy. He would get a nasty cold every year. The colds stopped six years ago when he started consuming a yogurt drink that contains live bacterial cultures.

The science: Many of the bacteria that live in the digestive tract have beneficial effects. Known as probiotics, these organisms have been shown to relieve many gastrointestinal conditions and to boost the body’s immunity, reduce blood pressure and decrease cholesterol.

Probiotics that live in the intestine make it harder for disease-causing germs to take up residence. People who have low levels of probiotics—after taking antibiotics, for example—get infections more often than those with healthy probiotic levels.

How to do it: Eat one or more servings of probiotic-rich foods daily. These include yogurt with live cultures, fermented soybean pastes (such as miso or tempeh), sauerkraut, probiotic-fortified soy milk and fermented cheeses, such as cottage cheese.

If you’re not eating probiotic-rich foods, you can take a supplement. Look for one that has a blend of probiotic organisms, such as Lactobacillus (L.) acidophilus, L. rhamnosus and/or L. bulgaricus, and follow directions on the label.

pH BALANCE

Until about eight years ago, Thomas Appell, age 56, got a cold or the flu along with a sore throat at least two or three times a year. One of his healthier friends explained his own secret—no sugar, no meat and a lot of vegetables. Appell followed the diet and found that he stopped getting sick. He investigated why the diet was working and discovered that the foods he was eating were predominantly alkaline. The traditional American diet is highly acidic. It’s possible that diseases thrive when the body’s pH—a measure of acidity/alkalinity—is out of balance.

The science: Proponents of the pH theory of health argue that our shift away from a plant-based, low-protein diet, which naturally keeps the body’s pH at “neutral” levels, created epidemic levels of disease.

Several recent books, including one from medical anthropologist and certified nutritionist Susan E. Brown, PhD, have linked disease to metabolic acidosis, which can occur when the kidneys don’t process acids fast enough.

What to do: Before you can achieve an optimal pH, you have to know your baseline. You can buy pH test-strip kits at pharmacies and health-food stores. Basically, you hold a strip in your urine stream, then look at the color. Most experts recommend testing the first urine of the morning. A pH chart that comes with the kit explains the reading.

Most people will find that they’re slightly acidic. To balance your pH, you will want to eat highly alkaline foods. These include most vegetables, legumes and olive oil. You also want to avoid foods that make your body more acidic, such as meats and processed foods. Thomas routinely checks his urine pH after a meal to see the food’s effect on his balance.

Even critics of the pH balance theory agree that eating more vegetables and fewer processed foods is important for good health.