Yes, I would say there is a definite prejudice against fat people. It is harder for them to get jobs, promotions, to adopt children, to start relationships and many, many more things.
I think there is not only prejudice against fat people but fat itself. How ridiculous is it for a package of gummy worms to post on its packaging that it is a "fat free food"!? Of course it is fat free it is made of mostly sugar! As a society we are so afraid of fat that we have even made different classes of fat. Is it saturated, poly, mono, or the dreaded trans variety?