I'm going to keep pushing for my overweight friend to lose weight
Has something caused your friend to gain weight recently?
Come on now! You're not his doctor, so you can't judge him for getting fat.
You're kind to be concerned about your friend's health, but he's the only one who can make healthy changes in his life.
I don't think you understand how serious it is. I don't think I  should just accept it.
You are allowed to be as concerned as you want for your friend. I just think that there is an underlying issue for which he eats so much that needs to be addressed first before anything.