Fox had doubts about transformation

Matthew Fox has opened up about the dramatic weight loss he committed to for his latest movie role.

The Lost actor shed over two stone to play sadistic killer Picasso in thriller Alex Cross, which stars Tyler Perry as the title character.

Speaking at the film's Los Angeles premiere, Matthew explained: "Whenever I read scripts... I see images, and the first image that popped into my head was that he would look like this.

"I wasn't sure I could pull that off, I've never had to do anything like lose that kind of weight or change the way I looked that intensely, but I knew I had a lot of time, that part of it was an interesting challenge to me, so I went to work on it."

And the 46-year-old revealed dieting was the key to transforming his appearance.

"It's 75 per cent diet, that's what I learned," he said.

"I was quite athletic all the way through my college years, thought I knew my way around a gym, but the person I had helping me out on this project taught me a lot about nutrition and about exercise, and it was all stuff I did not know."