What makes fat people unpleasant to look at?

It is instinct for us to find this appearance unattractive. Very fat people have a appearance which indicates that they are not healthy for breeding and this is what instincts tell us to seek, a healthy person to have our children with. It is the same reason why rotten things appear disgusting, and large animals with a lot of teeth and claws appear frightening, because we are instinctive to avoid them.