Growing teenager

I told my son that he needs to watch what he eats so that he can get rid of stomach fat.

He has been gaining so much in the past 6 months! I had to buy him new clothes every 3 months and he even wear his dad's old clothes already. I know he is a growing teenager, but whenever he sees food, he just have to eat them. And whenever I sees him, I stopped him. But he thinks I'm starving him to death. Help! Is this normal for 13-year old?