Mark Wahlberg has revealed how difficult it was to drop more than 60lbs for his latest movie role.

The Boogie Nights actor plays a college professor who is also a high stakes gambler who runs afoul of a loan shark in The Gambler, which also stars John Goodman.

Speaking on the red carpet at the film's premiere at AFI Fest in Los Angeles, the Hollywood star said he resorted to a liquid diet to lose even more weight than he did for his breakout role.

"It just started happening. The director Rupert Wyatt said "get as thin as possible" and once I start doing something I get obsessed with it.

"For Boogie Nights I got down to 138lbs so I thought I had to beat that, so I beat that by a pound but at 42 it's not as easy. I was 25 back then and all I literally had to do was smoke some cigarettes and eat tomato soup.

"This time it was exercise and a liquid diet for six weeks and jumping rope for three hours a day."

But Mark said the physical discomfort of losing 61lbs was worth it for such a satisfying part.

"That was an interesting thing to do because I wanted my whole world, other than detaching to be with my wife and my kids, to be about this. Between preparing to be believable as a literary professor and being believable looking the part, I had to do what I had to do."

He added: "There were so many pros and not too many cons, apart from having to lose the weight and be miserable for a few months. It was well worth it.

"The heart and soul of the film is a guy who is brutally honest and is not going to succumb to anybody else's rules, he will do his own thing. That's why his students love him, they find it extremely entertaining and cathartic.

The Gambler is released in the UK on May 1 2015.