Well, I’m pretty convinced that for many people it is not a sin, and that we should be very slow to judge or assume that someone is a glutton because they are overweight.
As has been said, there are medical conditions that predispose people to be overweight, and perhaps the commonest cause is lack of exercise in our Western way of life, where it is all too easy to be a couch potato. Then there’s the junk food problem, too-large portion sizes (and this, if you will please not be offended if I say so, is perhaps a particular characteristic of American fast-food outlets and restaurants, as many people who have visited there comment on it).
But there are also many who eat for comfort, and this is where I just don’t know about the culpability aspect, as I once struggled with it for a great many years, and all my efforts and guilt-trips got me nowhere. I prayed, I read about the issue, I just felt hopeless.
I can only say that God delivered me from it a few years ago - I know I could not have done it myself. I will always be grateful to Him for this. But at the same time, I am not presumptuous about it. Like any recovering addict, I will never trust myself to be “cured”.
So - there’s no way I am going to think harshly of overweight people, and I’m sorry to see people (like you, perhaps ThornGenX!) judging themselves severely, when perhaps they should deserve only sympathy.
God will help, in His own way and time, if you trust Him, and maybe follow Seek1st’s programme or something similar.