He wants to come in as big as possible he won't cut the food until the last minute. He is probably eating 6-8 meals a day right now. The "gut" is food and it will be gone on stage.
He's never been out of shape on stage. His stomach will probably be as tight as it usually is.
These guys need to watch out though, there comes a point of no going back once the gut is ruined. (Ronnie, Phil, etc).