No because not all people are fat because they are gluttons. (it's a Glutton not a 'gluten'. Gluten is a chemical found in wheat that many people have problems with).
No it is not a sin to be fat, some battle being overweight all their lives! Because of our imperfection and the different medical reason there are those that are overweight! Ask any person that is over weight if they enjoy being overweight! NOT ONE will say they like the way they look, they are embarrassed when eating out, and finding a table where the chairs will support them let alone a place where they can set down! I know some that eat in their car rather than at a restaurant because they just can't walk in and set down like the rest of us. I met a friend for pizza and when we walked into the pizza place they turned around and walked out embarrassed. I didn't know what was wrong until he pointed out the chairs and then I seen what he was talking about. I told him I'd see if they had a sturdier chair and he just turned and walked away with "no"! He has a medical problem where if he doesn't eat a minimum of 3500 calories he could pass out and he can't loose weight unless he eats over 3500 calories! He has tried every diet in the book and thought he was going to die because of his weight, none of them worked until he went to a doctor that found his problem!
But that doesn't stop people from starring at him every time he walks into a restaurant! I never realized what overweight people go through before, now when I see an overweight person my views have changed! No one is fat because they want to be fat!
Do you know that if you are 50 lbs overweight that is considered morbid obesity?