Lactose intolerance doesn’t prevent digestion-in fact aids it somewhat. But people who have lost significant lactase have undesirable actions with lactose and it is not worth using dairy.

So a little digging shows that the doctor was only partially right.

So what is funny - he made me stop my daily milk and 40 years later, I discovered I could not have dairy even in ice cream. Almost over night. Took me a long time to lose my lactase. Ha. (Really think a stressed gut was the problem, and the gut has a memory. IDK)