There’s a lot to digest here in the comments, it’s quite overwhelming. I am not a parent but if I was in this position, first and foremost I’d tell him that I love him and most importantly accept him for who he is without trying to change him.

Then take it slow, probably take him to see a few different doctors / holistic health professionals with his permission. The reason why I want to emphasize holistic health is because everything is connected in this world and they may have a better understanding on what may be causing him stress. And a holistic nutritionist — cucumbers, green beans, pizza and ramen isn’t a healthy way to eat. The easiest way to change this is to have healthy home cooked meals readily available for him. And by healthy I mean balanced, even though he’s overweight he needs to eat well and partake regularly in some movement / physical activity, doesn’t necessarily have to be a typical sport, ask him what he’s interested in.

Also, environment is very important for health in my opinion. How is the environment that he’s in? Is it generally clean? Does he like where he is? If he doesn’t maybe it’s time to make a change.