Self-esteem could be an umbrella in which to pull your examples. People will find themselves down mentally when they don't fit into what the media lays out for them. That could in turn make them go to drastic measures to confine to it. Surgery, unhealthy diets, eating disorders (like bulimia, not eating, binging, etc), anorexia, and such. Most of the American population isn't super skinny. I don't have any factual evidence but you can look that up.
Good luck on your essay!