Well obviously, back in Willis's early days when he went by the name of Hendrix, he was much skinnier so there was no weight issue. But probably in the eighties when he was krunked out on drugs, living on the streets of Chicago, he gained the weight. I'd give him a few more years.
http://www.monzy.org/wesley/ is an informative site about Willis. Plus, at the bottom of the page is a Wesley Willis song generator, so you can see what it is like to have the creative song writing ingenuity of this rock legend.