Not all bacteria are bad. Human digestive tracts are loaded with trillions of bacteria that aren’t harmful and can be beneficial or even crucial to health. Probiotics seem to change how the immune system reacts to invading microorganisms. They may compete with harmful bacteria or enhance the immune system. Also, they may help calm the immune system’s overreaction in ways not fully understood. And they may help restore or maintain proper bacteria balance in the intestines, which can be upset by antibiotics or invading microorganisms.

Well-done studies suggest that probiotics are effective in treating and possibly preventing diarrhea, caused by antibiotics or certain infections, or that occurs during travel. Strains of lactobacillus and Saccharomyces boulardii seem to be the most effective bacteria to treat diarrhea.

The evidence is less conclusive in other areas, such as whether probiotics might reduce symptoms of irritable bowel syndrome or prevent vaginal or bladder infections. But studies haven’t shown any harm in taking probiotics.

Probiotic supplements come in capsules, tablets and powders. While exact doses haven’t been determined, the general consensus is that a daily dose of about 10 billion colony-forming units is needed to provide benefits. Some foods contain probiotics, such as Dannon’s Activia, Yoplait’s YoPlus, fermented milk products such as Dannon’s DanActive, miso, tempeh, some juices, soy products and those containing kefir. While some foods naturally contain probiotics, the amounts probably don’t reach therapeutic levels.

Consulting a physician before starting probiotics is always a good idea. The care provider can offer recommendations on appropriate probiotic strains for specific health conditions as well as recommendations on reputable suppliers.

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