Common Symptoms of Lactose Intolerance Lactose intolerance refers to a digestive system disease caused by the body\’s incomplete decomposition of lactose or lack of lactase. The disease increases with age and is more common in Asians and blacks. Patients present with persistent flatulence, diarrhea, abdominal pain, and constipation. If they continue to drink milk, yogurt and other dairy products, they will have diarrhea many times and fishy stools, usually accompanied by foul-smelling exhaust. Diagnostic methods of lactose intolerance: Lactose intolerance can be diagnosed through hydrogen breath test, plasma glucose index, lactase