I don't know how fat is fat, but I have a pretty wide friend who comes over with some regularity. He used to be a pro baseball player, for the Cincinnati Reds. First baseman, big guy. He's comfy as hell in them, in fact too comfy. His snoring is not quiet, my friends can tell you!
He's watched more movies at my place than I can remember. He loves the seats. The actual "back" where your back is touching is real leather. All the way down to where your legs are being supported. Its the arms, and the actual "BACK" of the seat that is not real leather.