Common among populations of African, Asian and Native American descendants, also transiently after an acute episode of gasteroentiritis. History: Preseowith abdominal bloating, flatulence, cramping, and watery diarrhoea following milk ingestion. Diagnosis: Often treated empirically with lactose free diet. Hydrogen breath test reveals increased hydrogen following the ingestion of lactose. Treatment: Avoidance of dairy products; oral lactase enzyme replacement.