When you get back to Bowser's Castle later in the game, there's a branching path just before the throne room. Go left instead of up, and you'll find the dining room Bowser was in before. There, you can eat more to fatten him up again and return to the Flab Zone.
Your signature is something you want to say in every post. And I want to say "Let's all work together to make a better world for everyone."