I personally do not think he's fat...it's just the art style of the game...and his Kimono... I mean, take WW Phantom Ganon for example. he's not fat, and he is an exact copy of Ganondorf, so....Ganondorf isn't fat. IMO.
WW Ganon was a boss. His plump physique made it seem like he just didn't care. All he cared about was power, and the final battle with Ganon in WW was just so cool. The way he moved around with such precision, his plumpness obviously isn't a factor anyway and just made him all the more intimidating.
@TheBlueReptile i agree. now i don't have the game so i don't know the exact timeline. but if it's before OoT the he had a serious workout. but if it's after OoT he sat on his fat, lazy, butt for who knows how long.
We can safely assume his robes had something to do with it. Heck, who's to say he didn't gain weight during the time he spent sealed away? lol Graphical direction/design might have to do with it as well; not to mention the fact that the game [story] suggests that he's aged a bit. In my opinion, an appearance similar to Ocarina of Time would look funny as hell in the cel-shaded graphics/design of The Wind Waker to be honest.
In spite of what I said before in this thread, I like to think WW Ganondorf's weight and body type might be similar to Phantom Ganondorf's of the same game, especially given his origins as puppet of shadow crafted (to some degree) by Ganondorf in his own image. His robes appear to mask his true weight.
He might look fat but he was totally the most hardcore. He freaking slapped zelda and punched out Link twice! I don't think he has ever done that in any other game. WW Ganon was crazy!