The Promise of Probiotics

Can friendly bacteria keep you healthy?

Many people have never heard of kefir, a cultured milk beverage. But it's a staple in the home of Rebekah Smillie, a parent in Newton, Massachusetts-along with yogurt, naturally fermented sauerkraut, and occasionally even kimchi, a Korean pickled vegetable dish.

Smillie keeps these foods on hand because they contain high levels of probiotics, so-called "friendly bacteria" purported to have beneficial effects on human health. She believes her 8-year-old son's love of yogurt and kefir helps keep his asthma and eczema in check, "although there's not much interest in the kimchi."

Smillie may be onto something. Growing numbers of studies are suggesting that these tiny, living organisms-they're alive when you eat them, and stay alive in your digestive system-fight digestive disorders and help boost our ability to fight off some infections. But are they as effective as their proponents claim? While the verdict isn't fully in, current research supplies some promising leads.

How They Work

Trillions of beneficial bacteria already reside in our intestines, where they assist in digesting food and fighting off harmful bacteria. But illnesses and medications, such as antibiotics, can reduce their numbers, allowing the harmful to outnumber the helpful. When this happens, taking a probiotic can help tip the scales back in a healthy direction, says Frank Lee, Ph.D., a nutrition researcher at the University of Vermont. "Probiotics improve the balance of intestinal microflora."

It's not surprising then, that probiotics show most promise in digestive disorders, helping to prevent and treat diarrhea in particular. Recently, an Irish study found that people with irritable bowel syndrome who were given daily doses of a probiotic-laced malted-milk drink had less abdominal pain, bloating and constipation than a similar group taking a placebo.

Probiotic bacteria may also have a role in treating allergies, such as atopic eczema. When kids were given probiotic supplements for six weeks, their eczema symptoms were significantly reduced compared to those of a control group. The success of probiotic therapy in the treatment of bacterial vaginitis is also well documented. There's even tantalizing evidence hinting that probiotics may help fight the common cold: Earlier this year, German investigators reported that a probiotic-enhanced vitamin and mineral supplement shortened common-cold episodes by almost two days.

Probiotics won't cure everything that ails you, however. While many people use them to treat Crohn's disease, ulcers, high cholesterol, lactose intolerance and constipation, there aren't yet enough data to make firm recommendations, say experts. And pregnant or breastfeeding women, infants and anyone whose immune systems might be vulnerable to serious infection, such as chemotherapy patients, shouldn't take them without consulting a doctor first. Still, the promise of probiotics is strong enough that UVM's Lee and others think even healthy people can benefit from regular consumption.

Shopping Around

If you want to give the beneficial bugs a try, avoid using supplements, which currently aren't closely regulated and don't always deliver what they promise. "One-third of the supplements we tested had less than 1 percent of what was promised on the label," says Tod Cooperman, M.D., president of, an independent organization that has tested the probiotic content of 25 products.

Instead, get your probiotics from foods, especially those in the dairy case, says Lee. "Dairy food is an almost perfect vehicle for delivering probiotics." Compounds in products like yogurt and kefir shield probiotic bacteria from acid and bile as they travel through the digestive system, he explains, and they also provide bacteria with compounds (known as prebiotics) that help them thrive. Yogurt is a particularly potent source of friendly bacteria, such as Lactobacillus, outranking many supplements; when buying, check the ingredient label for the words "live and active cultures" or look for the "Live & Active Cultures" seal from the National Yogurt Association, which ensures a minimum of 100 million live cultures per gram.

Nondairy sources of probiotics, such as tempeh, miso, and kimchi, also provide beneficial bacteria, though their actions are less well documented, says Lee. Whatever probiotic food you choose, check the expiration date to ensure it's fresh: the longer a probiotic-containing product hangs around, the more beneficial bacteria die off. Refrigeration keeps them viable longer.

As researchers throughout the world continue to tease out the benefits of probiotics, there's no reason to wait for their findings to dig into probiotic-rich foods now. "They're pretty harmless," says Lona Sandon, R.D., assistant professor of nutrition at the University of Texas Southwestern Medical Center in Dallas. "Why not try them and see if they help?"

How Much Is Enough?

There's no recommended daily dose of probiotics, but research suggests aiming for 1 billion to 10 billion live bacteria cultures (measured in Colony Forming Units, or CFUs). Since bacteria counts are rarely found on food labels, focus instead on eating a serving of a probiotic-rich food every day. A cup of kefir, or yogurt labeled "live and active cultures," for example, will put you well within that range.

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