His director Darren Aronofsky has ordered him to look even bigger than he did in 'X-Men Origins: Wolverine' two years ago.
"It's 6,000 calories a day. It's rough," the Daily Mail quoted him as saying.
The 42-year-old Australian is also following an intense fitness regime and has already gained around 20lbs heavier than he was in 2009.
"Right now, I'm at 210 [15st]," Jackman said of his current weight.
"Darren said with the last one, 'Hey you looked great, but you're so tall that in those long shots you looked kind of like Clint Eastwood, and that's not Wolverine'.
"He said that Wolverine, in the comics, is powerful, stocky...he's short and thick. So he said, 'I want you to go there, get bigger'.
"If I have a massive heart attack, well, you tell everyone what I was going for," Jackman told the LA Times newspaper.
The actor promises the new film will be "the best of the bunch."
The 'Wolverine' is scheduled for a 2012 release. (ANI)