Probiotics are foods or supplements that contain "good" bacteria that may help with digestion and offer protection from harmful bacteria. Some of the ways they are thought to promote health include suppressing the growth of potentially harmful bacteria, improving immune function, enhancing the protective barrier of the digestive tract, and helping to produce vitamin K.

Nutritional supplements and foods such as yogurt, fermented  milk, kefir, miso, and some juices and soy drinks contain probiotics.  Once ingested, probiotics colonize the intestines and other parts of the body and can sustain themselves unless they are destroyed by antibiotics or other factors.

Several valid studies have looked at probiotic use in adults, focusing on the strains Lactobacillus reuteri, Lactobacillus GG, L casei, L acidophilus, and S boulardi. Although they varied in dose and probiotic strain, in six out of seven of the studies, probiotics shortened the course of diarrhea or decreased its severity.

Read product labels carefully, looking for a statement that the product contains "live and active cultures," such as lactobacillus.

Most people can safely add probiotic foods to a healthy diet. People who are immunosuppressed should seek medical advice before using probiotics.  If you're considering taking probiotic supplements, check with your doctor or dietitian to make sure the supplements are right for you.