The star is only allowed to eat between certain hours of the day as he gears up for filming scenes as superhero Wolverine in X-Men: Days of Future Past.
Jackman reveals he must consume 5,000 calories a day to bulk up, but he has to stuff them all in between 10am and 6pm.
He tells Entertainment Weekly, “I’m quite a skinny person by nature so I’m eating ridiculous amounts of food…
“What I do is I eat everything in an 8-hour period… It’s called the 16-8 diet. For 16 hours of the day I fast, so I don’t eat. So between 10 in the morning and 6 at night – this is why I’m burping because I ate a steak literally before I came out – I eat 5,000calories and then I eat nothing. I literally talk to myself like I’m training: ‘One more mouthful, come on man, you can do it. Just one more mouthful. Half a chicken breast to go and you’ve got it! Only two meals left.'”
Jackman previously shed weight for his role in Les Miserables by restricting himself to a liquid-only diet.