Probiotics are a type of good bacteria. They help keep the natural balance of organisms in the intestines. They reduce the growth of harmful bacteria to help keep the digestive system healthy.

The normal human digestive tract contains about 400 types of probiotic bacteria. The largest group in the intestine is lactic acid bacteria. This includes Lactobacillus acidophilus, the type found in yogurt with live cultures. Yeast is a probiotic too. Probiotics are also sold as dietary supplements.