sounds to me like he had other untreated medical conditions, something akin to an obsessive compulsive disorder centered around the food he ate.
Shame he couldn't have gotten more help before it was too late, but at 20 he's a grown up and can do what he likes even up to and including refusing treatment or counseling or taking vitamins or anything. Grownups dont have to do what docs tell them to do, or even what their mother tells them to do...