"Good" bacteria found in food and dietary supplements may help ward off illness. Called probiotics, these bacteria been shown to secrete protective substances that turn on the immune system and prevent pathogens from taking hold. The strongest evidence for the benefits of probiotics is in treating diseases caused by harmful bacteria in the gut that cause severe diarrhea. When beneficial organisms coat the surface of the colon, then bad bacteria are blocked from attaching to and invading the wall of the colon. Foods that contain probiotics include yogurt, a fermented dairy drink called kefir, and fermented vegetables such as pickles and sauerkraut. They are also available in pill form. Common dosages for adults range from 5 to 10 billion colony-forming units per day, in a single daily dose, with or without food.
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