When I talk to a girl things usually go well.. But then she gets to the whole "I'm fat" thing. When you get into those situations how do you get out? What do you say to either change the subject?

It's incredibly annoying and a huge attention hog, so I need to know what to say so I don't feed that to make her say it more.

Edit: the Girl i talk to says that she herself is fat. Not me.