A STAUNCH supporter of method acting, Michael Fassbender dropped to just nine stone to play Bobby Sands in the 2008 biopic of the IRA terrorist's hunger strike.

The film, Hunger, was feted at festivals across the world and placed the actor firmly on the map. But while he endured physical extremes for that movie, the 34-year-old insists his latest film, Shame, a searing study of sex addiction that has already won him Best Actor at the Venice Film Festival and a Golden Globe nomination, was mentally distressing.

"I had to lose weight for Hunger, but I had a timetable to stick to. So I just ate 600 calories a day and got through it," says the actor in an Irish lilt. "But Shame was pretty disturbing: the idea of what my character is about, the relationships and intimacy and how that's difficult for some people."

Fassbender plays Brandon, a New York office worker with an uncontrollable libido whose life is disrupted by the arrival of his sister (Carey Mulligan).

"The idea of sexual addiction is a grey area. All of us were probably introduced to it through celebrity stories, so there's a certain public perception that it's a self-indulgence within that world," muses the German-born actor, who's wearing jeans, grey T-shirt and a black biker jacket. A bundle of restless energy, he fidgets in his seat and scratches his coppery stubble, his bright blue eyes glimmering with unabashed mischief.

Shame reunites Fassbender with Steve McQueen, the Turner Prize-winning artist-turned-director who gave him his breakthrough in Hunger, and screenwriter Abi Morgan, currently riding high with The Iron Lady starring Meryl Streep.

"The film has this great humanity. It's tough to be human. We're all fragile in our own way and each of the characters needs somebody to help them. I thought that was quite moving."

Bleak and melancholic, the film is dominated by long scenes with limited speech punctuated by Mulligan's heartbreaking rendition of New York, New York, but Fassbender insists there's also a sense of optimism.

"Brandon's trying to deal with his addiction – and that's enough hope for me," he says.

While Fassbender's striking performance has garnered critical acclaim, there's also a whole lot of hoopla surrounding the explicit sex scenes and uncompromising nudity.

Fassbender's bewildered by all the fuss.

"People are saying, 'Oh my God, you're naked! What's that going to do for your career?'.

" I'm not a politician. My job is to facilitate characters. I'm a storyteller."

However, that's not to say he didn't feel embarrassed on set.

"Of course," he laughs. "I didn't feel comfortable parading around naked in what was essentially, at the beginning, a room full of strangers, but it had to be done. It was an essential part of getting inside the psyche.

"Besides, my imagination was much more devious than what was in the script."

In preparation for the role, Fassbender got in touch with sex addicts: "I asked them to tell me stories so I could get an idea where certain motivations were born and how somebody suffering from this condition deals with it," he explains.

And then he just worked with the script: "I'm spending a lot of time with the character and getting to know him.

"It's about trying to understand and relate to him, as opposed to judging. That would be a mistake."

Born in Heidelberg, Germany in 1977 to Josef, a German chef, and mother Adele, from Larne in the north of Ireland, the actor's family moved to Killarney when he was two.

His interest in acting was sparked when he started drama classes. Then, at 19, he moved to London to study at the prestigious Drama Centre and in 2001 got his first TV role in the Steven Spielberg-produced Band Of Brothers.

"I thought that was it," he recalls, but admits it was an "arrogant and stupid" way of thinking, as he didn't work much afterwards, combining the odd TV series and small screen movie with pulling pints for extra cash. It was only after he was cast as Stelios in the 2006 CGI blockbuster 300 that he could finally earn a living from acting. And then along came Hunger, which won numerous plaudits, including the Camera d'Or at Cannes.

"Steve McQueen changed my life with Hunger," he says and reveals it's why he didn't even read the script for Shame before accepting the part.

In the last couple of years, he's continued his fondness for playing complicated characters, from Lt Archie Hicox in Inglourious Basterds to Magneto in X-Men: First Class and Mr Rochester in Jane Eyre. And 2012 will prove no different.

Following Shame, Fassbender appears in Steven Soderbergh's espionage thriller Haywire, and David Cronenberg's A Dangerous Method, in which he plays Carl Jung opposite Viggo Mortensen's Sigmund Freud.

After that, he'll star in Ridley Scott's Alien-inspired Prometheus before reuniting with McQueen for Twelve Years A Slave, alongside Brad Pitt.

n Shame is released in cinemas tomorrow, Haywire on Friday, January 20, and A Dangerous Method on Friday, February 10

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