Hope you are able to find ways to support your son to make small, positive changes to his menu in a way that he can accept and even perhaps enjoy?
We have a number of neuro atypical and divergent members on the forum who have been able to make adjustments to their ways of eating. Some have even made it into something of an engaging and interesting 'project' to find ways of preparing and choosing lower-carbohydrate foods that satisfy their sensory needs while being kinder on their BG levels.
It's a tricky balancing act for sure - but he isn't alone in having to face it, and others have been able to find a way through the complexities of balancing both conditions, so there is hope. 🙂