I think when we were young nobody listened to or believed children when they complained about feeling bad with no obvious symptoms or proof. It was "walk it off" and "suck it up". People with intolerances just kept it to themselves and tried to avoid or suffer. My mother as a young toddler suffered multiple bone breaks and dislocations, and lived her life in pain with Ehlers-Danlos syndrome but wasn't diagnosed until a couple years before her death in her 50s. She had a degenerative disease with obvious symptoms but nobody ever caught on. They just thought she was clumsy and a hypochondriac.