A lot of body fashion (i.e. skinny girls being desirable one decade, the next decade curvy girls are 'in') is the same as any fashion and fads, it's about social status and it often revolves around that which is hardest to achieve. It's why in times when food is scarce, large people are seen as desirable (it suggests that they have a steady access to food, they can provide for a family, large women in particular will bear healthier offspring) and in modern times when junk food is plentiful and cheap and exercise is unnecessary, being skinny is seen as desirable (it suggests that they are hard working, they have self control and mental strength).
I really wanted to find some links that explained this better but Google only offered me crappy pop articles about 'what men want'.
In fact my search skills are being extra crap because I can't find the article I read about this, now, either, but maybe someone saw the programme on TV last year about how blind people develop attraction to other people. One (blind) guy talked about how he was going out with a girl he really liked, then his brother told him she was ugly, so he broke up with her. It's because of the social status, people don't want to be perceived as inferior because the person they're dating is perceived as inferior, and if they're big enough to get over that, the point of what I'm saying is;
People don't want their friends to be perceived as inferior for dating someone perceived as inferior... because then they are perceived as inferior for having friends that are inferior!
... well, that was an awkwardly written post.
