I'd say dieting and eating disorders were contributing quite a bit. Famine, whether self-inflicted or imposed externally, does all sorts of subtle and less than pleasant things to hormones (and it wouldn't surprise me at all if it impacted one in utero more than any other time, though I imagine childhood and especially adolescence are probably pretty critical times as well).

Also, I do not actually believe obesity to be a disorder in of itself. (Some day, in an alternative universe where I have time to do so, I could write a great many paragraphs on this.)