The stomach is the first line of defence of the body against possible disease organisms. The low pH (or high acidity) of the stomach kills most foreign bacteria before they pass into the intestines. If this weren't so we would be sick more often. By consuming a very large number of bacteria in yogurt, some survive and pass through the stomach. However, the environment in the intestines is not friendly either. Our intestines are home to a wide variety of different bacteria; some of these bacteria are beneficial and some are not. The yogurt bacteria must compete with the normal intestinal bacteria for nutrients and sites to adhere to. Because the yogurt bacteria are foreign, they do not find adhesion sites along the intestinal wall and are quickly flushed through the intestines and are excreted in the feces.