When lactose is not digested, water is retained in the bowel. This results in bloating and watery diarrhea. Lactose that passes into the large intestine is fermented by bacteria. This produces carbon dioxide, hydrogen, and methane. This in turn leads to bloating, cramping, and flatulence, or passing gas.
Lactose intolerance causes abdominal bloating and discomfort.
It also produces watery diarrhea and gas. A temporary lactase deficiency sometimes follows a stomach virus in children. When the child has diarrhea with the stomach virus, his or her intestines are stripped of the enzyme lactase. The child then has trouble digesting lactose when he or she drinks milk products. This produces watery diarrhea.