Sure, Pierce has talked about being something of a fat kid growing up, and when he does trim down, as in the fall of 2008, it doesn't seem to stick.
Now that he's getting older and slowing down a tad, getting and staying in shape is probably the more important for his productivity and maybe for minimizing injuries as well. It'd be nice to see him come back slimmer this fall and stay that way. I could say that the sterling examples of KG and RA don't seem to have rubbed off, but maybe their influence has kept him from chubbing up more: he's never come close to a Big Baby, let alone a Sweetney.