Hugh Jackman has revealed the brutal diet he was on in preparation for his starring role in the upcoming film, The Wolverine.

Jackman admitted in an interview on Thursday how hard it was to get ready to play the mutant Wolverine in the X-Men franchise. Not only did Jackman go through a punishing workout routine to get himself in shape for his character's upcoming solo effort, he had to pile on the calories.

"You actually have to eat a LOT, and I'm quite a skinny person," Jackman said in an interview with Sirius XM satellite radio. "So I'm eating ridiculous amounts of food. I quite like everything I ate, but it's more bland. Chicken breasts, but steamed, no salt. And steamed spinach."

View interview with Jackman below.

According to Jackman, timing is everything when he's pouring on those calories.

"When you're bulking, you're just eating so much food," Jackman said.

"What I do is I eat in an eight hour period, it's all the rage this diet now. It's called the 16-8 diet. For sixteen hours of the day ... I don't eat. Between ten in the morning and six o'clock at night ... I eat 5,000 calories. And then I eat nothing ... it's more about, 'This is a disgusting amount of food, I can't eat another bite.'"

Jackman began work on The Wolverine soon after he wrapped up his role as Jean Valjean in Les Miserables. He fasted and cut back on his water intake to play Valjean in order to capture the character's physical transformation as he wasted away throughout the course of the story. Jackman said that between the physical and emotional aspects of the role, Valjean was his most difficult job to date.The actor cited The Wolverine and Les Miserables as his two most physically challenging roles and his starring role in the Broadway musical The Boy From Oz, in which he played Australian singer and songwriter Peter Allen, as the close third.

The Wolverine opens in theaters on July 26.

Watch a trailer for the film below.