Lots of people think there is no connection between people's behaviour around someone and that someone's weight. Because of our society that pressures girls & women to look beautiful and be skinny, mainly girls will take other girls less seriously if that girl isn't pretty or skinny or perfect. Other girls may not feel the respect for a over-weight girl, because in pretty much all schools the pretty, skinny, perfect girls, are the ones which get power.
When I was younger I thought make-up, and designer clothes, and being skinny was all stupid. I still think it is stupid now, but I see myself doing it. I use make-up now, I still hate designer labels but whatever, and I haven't eaten in a day & a half. Nobody's actually said to my face I'm fat, it was my own choice to starve, but . . . I feel more confident when I haven't eaten. I'm guessing it's the normal society peer pressure, because I've gone on different sites and I've found many girls thinking the same thing. But ultimately, it's my choice so I can't play the blame game.
So, in conclusion, sadly, yes that is true.