Actually, you'd be surprised to know the amount of Korean, Japanese and Chinese young ladies who fight to lose kilos to be as slim as possible... As well as all the surgical operations/cosmetic changes to try and copy certain Occidental features.
That said, some eating disorders do not have as an end to be more "sexually appealing", thoug most do.
There is also a lot of hypocresy as you put it, of girls who aren't fat who think they need to lose some weight, but probably realise they don't need it (not as much as other people), and will thus say that to other girls to avoid them falling into the same frame of mind.