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.'"