According to wikipedia, Lactose intolerance, also called lactase deficiency, is the inability to digest and metabolize lactose, a sugar found in milk. It is caused by a lack of the enzyme lactase in the digestive system, required to break down lactose. It results in symptoms including abdominal pain, bloating, flatulence, diarrhea, nausea, and acid reflux.

Milk sugars found in milk products cause dumping after gastric bypass surgeries. To avoid the symptoms of dumping look for low sugar, low sugar alcohols, and low fat varieties of milk, yogurts, and cheeses.