How do you address excessive weight gain for a non-verbal autistic child?

I wish i knew!! The child can not communicate and does not understand that he needs to eat in moderate amounts, its a challenge specifically when they are taking medications that lead to increased appetite!! It is a constant struggle to reduce the amount of food. The experience i have is someone who turns aggressive! if you do not provide the food, he really does not understand! Behavior change for these children is uncomfortable! Another 'young adult' autistic that i know is totally the opposite, he does not want to eat at all, and if he has to eat it has to be the same diet, no change!! Its very true that every autistic child is 'quite unique', however i still have the same challenge, 'how do you address the weight?' I wish i knew!!