gluttony is the sin of intemperance with eating and drinking, it’s not just overeating, but also under eating, being to picky, being willing to hurt or deprive someone else(such as your family) for the food you love,or just having an inordinate desire for the pleasure connected with food or drink,
there is a bit of breathing room of course, because we need to eat, and there’s nothing wrong with eating more than you need, as long as it’s not to much, but mostly the sin lies in your own desires, and how you give into them.
but to answer your original question, no, being obese in and of itself is not a sin, especially when many become obese through no fault of their own, such as those who have certain operations that inevitably cause weight gain(i know a few like that) or those who take certain depression medications, or those with thyroid problems, and various other things.
also, most processed foods are just bad for you, they are loaded with bad ingredients, empty calories, hydrogenated oils, badly processed syrups and sugars, and just an insanely long list of other things that cause poor health and weight gain,
my sister for example, use to be fat, she started getting alot of these things out of her diet, and eventually went as organic as she could, and now she looks great, and i know many others who have done the same…
and i’m not trying to start a conversation about food itself here, but i just wanted to point out, alot of people complain that they don’t eat alot, and yet they gain weight real bad…and i just can’t help but think that our problem with obesity here and elsewhere is not gluttony, but just the food itself…which when you get right down to it, the proof is in the pudding(no pun intended) and you’d just have to try it for yourself to see(for those who do have weight problems.)
ok well that’s all, hope this helps, take care.