Lactose intolerance is the inability to digest lactose, the natural sugar found in most dairy products. Lactase, an enzyme our bodies produce, breaks down lactose into simpler units during digestion. Some people do not produce enough lactase or do not produce lactase at all. In this case, the lactose does not get broken down into smaller units. Instead, the lactose is fermented in the colon. This fermentation process often produces common symptoms of lactose intolerance, including bloating, abdominal gas or pain, diarrhea, and nausea.