A lactose free diet means eating foods that have no lactose. Lactose is a sugar that is a normal part of milk products. Some people do not break down lactose well. They may not have enough lactase, the enzyme that breaks lactose down in the body. Or, their body may make lactase that does not work properly. This may cause gas, bloating, cramping, or diarrhea when they eat or drink milk products. Following a lactose free diet may prevent these problems.