People that have used to be fat, and then lost a lot of weight, will know how brutally different people will treat you. Whereas you'd practically be a ghost before weight loss, random people will suddenly look you in your eyes, smile, even start conversations with you.

Some will of course argue that you losing weight will also make you more confident, and thus you become more approachable. I think there's a lot of bias against fat people, against "unattractive" people, etc.

This also shows in the classroom, work, etc.

Of course, actually being conventionally attractive will come with its own perks. People will go out of their way to help you, and to support you. Over time this could very well boost your ego to also become more confident and decisive.