The Truth About Probiotics and Your Gut

Last Editorial Review: 6/9/2010

What Are Probiotics?

By Peter Jaret
WebMD Feature

Reviewed by Louise Chang, MD

Probiotics are microorganisms such as bacteria or yeast that are believed to improve health. They are available in supplements and foods. The idea of taking live bacteria or yeast may seem strange at first. After all, we take antibiotics and use antibacterial substances to fight bacteria. But our bodies naturally teem with such organisms.

The digestive system is home to more than 500 different bacterial species. They help keep intestinal linings healthy and assist in breaking down food. Beneficial organisms are also believed to help regulate healthy immune response.

How Do Probiotics Work?

Researchers believe that some digestive disorders result when the balance of friendly bacteria in the intestines becomes disturbed. This can happen after an infection or after taking antibiotics. Intestinal problems can also arise when the lining of the intestines is damaged. Introducing new beneficial organisms in the form of probiotics may help.

"Probiotics can improve intestinal function and maintain the integrity of the lining of the intestines," says Stefano Guandalini, MD, professor of pediatrics and gastroenterology at the University of Chicago Medical Center. These friendly bugs may also help fight off diarrhea-causing organisms.

Probiotics and the Immune System

There's also evidence that probiotics assist in maintaining a strong immune system. "In societies with very good hygiene, we've seen a sharp increase in autoimmune and allergic diseases," Guandalini tells WebMD. "That may be because the immune system isn't being properly challenged by pathogenic organisms. Introducing friendly bacteria in the form of probiotics is believed to challenge the immune system in healthy ways."

Probiotics May Benefit an Array of Ailments

Although evidence is still being gathered, researchers say there are enough data to rate the effectiveness of probiotics for several specific illnesses. In 2008, a panel of experts at Yale University reviewed the latest findings. They concluded that probiotics are most effective for:

  • Acute childhood diarrhea
  • Preventing antibiotic-associated diarrhea
  • Preventing pouchitis, an intestinal inflammation that can follow serious intestinal surgery
  • Regulating immune response
  • Treating and preventing eczema associated with cow's milk allergy

The Yale University panel of experts concluded that probiotics may be helpful in other ways, although the evidence so far is less convincing. These include:

Probiotics may also be useful in unexpected ways. A study published in 2010 suggests that probiotics may decrease the risk of common childhood problems such as ear infections, strep throat, colds, and diarrheal illness. The study included 638 children aged 3 to 6 in day care centers/schools. The children who drank a yogurt drink containing a probiotic were 19% less likely to come down with a common infection.

Cautions About Probiotics

For the most part, taking probiotics is very safe and causes few side effects. "People in cultures around the world have been eating yogurt, cheeses, and other foods containing live cultures for centuries," says Martin Floch, MD, a professor of gastroenterology at Yale University, co-author of Probiotics: A Clinical Guide, and a consultant for the Dannon Company.

Still, probiotic supplements may be dangerous for people with weakened immune systems or serious illnesses. One study found that patients with severe pancreatitis who were given probiotics had a higher risk of death. More studies of probiotic use in young children and the elderly are needed.

Are Probiotic Supplements or Foods Best?

Probiotics come in many forms, including powders, tablets, capsules, and foods such as yogurts and dairy drinks. The form you take them in doesn't matter, experts say, as long as it contains enough live organisms to begin growing in the intestines. Experts say the effective dose varies widely, from as little as 50 million to as many as 1 trillion live cells per dose.

Specific probiotic organisms appear to be useful for particular illnesses, however. The bacteria Lactobacillus GG and the yeast Saccharomyces boulardii have been shown to be helpful for infectious diarrhea in children, for example. "But there's no evidence that Lactobacillus acidophilus, which is used in many commercial yogurts, has any benefits for diarrhea," says Floch.

Advice on Choosing a Probiotic Supplement

The FDA does not regulate probiotics as it does prescription medications because probiotics are in the same category as food and supplements. With growing evidence for their effectiveness, however, the FDA is reviewing their status and may regulate them more closely in the future.


According to the USDA, there is no difference between a “portion” and a “serving.” See Answer

"For now, the best advice is to choose products from well-known companies, especially those that have been tested in research studies," Guandalini says. Reliable products should indicate the name of the precise probiotic organisms they contain, as well as how many organisms a single dose provides. Many products also provide information on the scientific studies they use for their recommendations.

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Floch, M. Journal of Clinical Gastroenterology, July 2008; vol 42: pp S104-S108.

Merenstein, D. European Journal of Clinical Nutrition, May 2010, Epub.

Besselink, M. Lancet, 2008; vol 371: pp 651-659.

Sanders, M. Functional Food Reviews, Spring 2009; vol 1(1): pp 3-12.

Stefano Guandalini, MD, professor of pediatrics and gastroenterology, University of Chicago Medical Center.

Martin Floch, professor of gastroenterology, Yale University School of Medicine, New Haven, Conn.; co-author, Probiotics: A Clinical Guide.

Reviewed by Louise Chang, MD on June 09, 2010

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