many young women are left feeling either invisible or fat and unaccepted Salam sajad Because success and happiness are equated with being thin (society says so!) , and obviously that is far from being the case for everyone (in this case, women), the only choice that they have (because, again, not everyone can be thin) is to make themselves "invisible" to the eyes: that means not going to parties, not going out etc.. Or of course they can just appear simply as fat in front of others (which may be a hard thing to do) Or, they feel unaccepted meaning that if they show themselves as such they will feel the look of how society sees them.

I agree with Sumayya FS and Oliver about the general meaning of the phrase, and the fact that it is about the effect of the culture, but "many young women are left feeling either invisible or fat and unaccepted" is not about choices. It is about how young women are made to FEEL about themselves. Some young women who are not slim and glamorous feel that they are invisible. They have the impression that nobody takes any notice of them, because their appearance does not match the ideals of thinness and attractiveness. Meanwhile, others feel that they are being noticed, but that they are rejected because they don't fit the image.

It means, because of the new culture, a lot of young women feel unnoticed (invisible) fat and disliked (unaccepted).