I think in general, yes they do. *I* believe society places too much emphasis on looks, and we are programmed to believe skinnier is better.
For me personally, when I am skinny, I have alot of confidence and put myself out there more. Now after bubs number 3 and being about 20 kilos overweight, my self confidence is low and I have become a bit of an introvert. The few time I have gone clothes shopping etc, I think I put out there to leave me be IYKWIM?!?