You should try to understand what he eats and why. Is it just a lot of junk food? He might not be feeling full, because fast food is not very satiating. Try add

You should try to understand what he eats and why. Is it just a lot of junk food? He might not be feeling full, because fast food is not very satiating. Try adding more protein and fat in his diet and reducing carbohydrates. I'm not saying a ketogenic diet - just changing the proportions a bit to see if he feels fuller. You can try to help all you want but he's a grown man and will have to decide by himself. Show that he can eat yummy things that will keep him full - as long as he has a caloric deficit, he will lose weight. Eating salads all day won't satisfy anybody. Try eating meals with him. Good luck!