Support Grows for Healthy Bacteria
Clarified 8/3/07: An earlier version of this story refers to Lori Hoolihan of the Dairy Council of California by a surname she no longer uses.
Yogurt's not just a food anymore. It has emerged as a dietary supplement that promises benefits far beyond a slim waist. The old staple, along with other foods such as aged cheese and the dairy drink called kefir, contains newly touted probiotic bacteria. From improving digestion to preventing allergies, the reported properties of probiotics sound almost too good to be true—but a growing body of research suggests that some healthful bacteria, at least, might live up to the promise.
Probiotics include a variety of "friendly" microorganisms—certain types of bacteria and yeast—that may provide consumers with health benefits. It might seem counterintuitive to gobble bacteria for better health, but a healthy human gut teems with hundreds of varieties of bacteria, most of them harmless or even beneficial. Those friendlies, most commonly Lactobacilli and Bifidobacteria, vastly outnumber the body's human cells and help maintain a healthy digestive system in part by inhibiting the growth of potentially infection-causing microbes. It's a delicate balance.
Probiotics may be most useful when that balance becomes disturbed. Sometimes, a weakened immune system or a bad hamburger tips the scales in favor of the unfriendly microbes; at other times, a course of antibiotics that kills bacteria indiscriminately can leave the digestive system vulnerable. In such situations, probiotics may restore a healthy balance. Moreover, some experts say, taking a daily probiotic supplement might help prevent infections in the first place—and also combat allergies and even some chronic diseases.
However, the strength of the supporting evidence varies from one potential use to the next. While some health benefits from probiotics are well documented, others are only in early stages of study. Here are some major areas of investigation:
Intestinal Troubles: A large body of research shows that a daily dose of friendly bacteria can aid the digestive system in a number of ways, from improving regularity to preventing traveler's diarrhea. Sherwood Gorbach, a professor of medicine at Tufts University, says that the viruses that cause some cases of childhood diarrhea are especially susceptible to preventative probiotic use.
Antibiotics: Probiotics may also be useful during or after a course of antibiotics. A study this month in the British Medical Journal was just the latest confirmation that drinking a probiotic supplement during and after antibiotic treatment helped prevent diarrhea, which can develop as a consequence of that therapy. Antibiotics kill intestinal bacteria indiscriminately, making a person more susceptible to bacteria such as Clostridium difficile. "It's like an atomic bomb in your gut," says Gary Huffnagle, professor of internal medicine at the University of Michigan and author of The Probiotics Revolution. Taking probiotics to complement an antibiotic treatment is a "no-brainer," he says.
Immune System/Allergies: Recent research on probiotics has focused on effects on the immune system. Experts say that the friendly bacteria that normally live in people's guts "talk" to the immune system, helping to build immunity to dangerous microbes. Huffnagle points out that the signals can also prevent the immune system from becoming overactive and creating allergies. Probiotic bacteria, he says, "send an all's-well signal that says, 'We're all OK down here.'"
Urogenital Health: Women have long eaten yogurt as a natural way to prevent yeast infections, and recent research supports this folk remedy. Scientists have linked probiotic consumption to reduced numbers of yeast infections, and studies have shown that, at least in a petri dish, probiotic bacteria can inhibit the growth of yeasts like Candida, which commonly cause infections. Still, probiotics might work even better if women put the bacteria directly where they're needed. A recent study showed that a vaginal suppository containing two types of Lactobacillus bacteria that normally live in the gut can restore the balance of bacteria in the vagina, curing a yeast infection. Other promising studies have shown that regular consumption of probiotics might help prevent recurrent urinary tract infections in women.
Cancer? Ulcers? Teeth? Recent studies have shown that probiotics might aid a number of other conditions. One study indicated that probiotics can help fight Helicobacter pylori, the bug that causes stomach ulcers and gastric cancer. A series of animal studies has shown that probiotics could help prevent colon cancer, too. And some evidence points to probiotics potentially benefiting oral health. However, many experts are unconvinced. Gorbach says that while a few of the claims are promising, solid clinical trials are needed.
The health benefits sound great, but choosing which probiotics to include in a diet can be tricky. A wide variety of bacteria get touted as probiotics, but only some of them have proven health benefits. Experts recommend looking for a product that lists genus and species, rather than a vague term like "proprietary formula." Some bacteria species in the Lactobacillus and Bifidobacterium groups have been well studied, although each has a number of strains, and not all of them have been studied.
Another problem particular to packaged probiotic supplements is that the bacteria might die or degrade while the product sits on the shelf. Most probiotic supplements should be stored in the refrigerator and used promptly once opened, says Gorbach. "As soon as you crack that bottle, the organism will begin to deteriorate." Of several million friendly bacteria in a probiotic pill, he explains, only a few thousands or hundreds might be alive and active by the time you take it.
If aiming to get probiotics through foods, look for a seal that says, "live active cultures," says Lori Hoolihan, a nutrition research specialist with the Dairy Council of California. Hoolihan notes that probiotic foods like yogurt—and certain other products, including aged cheeses and the dairy drink called kefir—generally contain the added nutritional benefits of nutrients such as calcium, vitamin D, and prebiotics, a class of molecules that she calls "food for the probiotics."
In any case, eating live probiotics doesn't guarantee that they'll reach your intestines. Bill Costerton, professor of dentistry at the University of Southern California, is skeptical that probiotics could penetrate the intestines' defense system. "The gut is lined by a great big wall of mucus," he explains. The community of bacteria that exists in a normal digestive tract, he adds, "is pretty much bulletproof." However, he agrees with other experts that taking probiotics to aid a disturbed digestive system—such as one ravaged by antibiotic treatment—is probably effective.
But nutritionist Katherine Tallmadge cautions that it might be premature to start popping probiotic supplements, noting that some products have been associated with negative side effects, particularly in people with compromised immune systems. "I don't feel comfortable recommending them to clients just yet," says Tallmadge. "There's a lot we don't know about how they work." However, she says, foods that naturally contain probiotics, like yogurt, are probably a safe bet.
Probiotic treatment should not be seen as a substitute for medical care. Rather, experts say, the major benefit of probiotics is preventive. As Hoolihan likes to say, "A few million probiotics a day keep the doctor away."