Christian Bale: Hustle and flow

Christian Bale, who lost weight for previous roles, put on 20kg to play the pot-bellied conman in American Hustle

A close-up of Christian Bale's pot belly - in all its wobbly, hairy glory - fills almost the entire screen during the first frames of American Hustle, the new conman caper by director David O. Russell.

It prompts an audible intake of breath at a recent screening of the film in New York, where the audience is gobsmacked not so much by its girth - which is considerable - but the fact that once again, Bale has gone above and beyond what might be reasonably expected of an actor.

It is pretty obvious that he could just as easily have strapped on a prosthetic tummy - the bulge is so obscenely tumescent that it looks kind of fake, anyway.

Instead, the Oscar-winning star of The Fighter (2010) and The Dark Knight Batman trilogy (2005 - 2012) chose to gain the weight the hard way, putting on almost 20kg through a diet of doughnuts, cheeseburgers and other junk food.

Why go to all the trouble? The actor offered an explanation during a press conference in New York's Crosby Street Hotel earlier this month when the cast of the film, including Amy Adams, Bradley Cooper and Jennifer Lawrence, were asked about the allure of reinventing themselves for each movie.

"For me, it's studying people. It's nice," says Bale.

"Everybody dreams at night and tends to go a little insane. And that's acceptable, you know, because we're dreaming.

"To me, acting is sort of dreaming in a waking state because you get to study people and you get to go a little insane and be obsessive about something, and it's expected. And the more you are, the better it is. I find that very addictive."

As far as Bale's acting style is concerned, "insanity" might not be that much of an exaggeration.

The 39-year-old Briton is infamous for the lengths to which he goes in his movies, where he often plays tortured, brooding characters, such as the darker incarnation of Batman he created with director Christopher Nolan.

This frequently involves drastic and rather alarming physical metamorphoses - notably for The Machinist (2004), where he became deathly thin after dropping 28kg on a regimen of apples, salads, chewing gum and cigarettes in order to play an insomniac factory worker.

And once that film was completed, he had just six months to reverse this and put on 48kg for his next role, that of the muscle-bound caped crusader in Batman Begins (2005).

For American Hustle, which opens in Singapore this week, Bale makes himself over yet again, this time to play Irving Rosenfeld, a small-time crook who is caught by the Federal Bureau of Investigation and forced to help it run a sting.

As the slow-moving and bespectacled conman with a beer gut and an elaborate combover, the actor is virtually unrecognisable in this film, which is based on the real-life Abscam operations the bureau ran in the 1970s and 1980s to nab public officials on the take.

Even co-star and acting legend Robert De Niro, who has an uncredited part, did not recognise him when they were first introduced on set

Russell reveals: "After De Niro met everybody, he said, 'Who's that guy?', and I said, 'You just shook his hand, it's Christian Bale.' And he said, 'No, that guy', and I said, 'Yeah, that's Christian Bale!'

"He just stared, and I had to introduce him again."

For Bale, the physical transformations are always in service of his character and what make each one tick beneath the surface.

So while American Hustle was enjoyable to work on because "the characters are really colourful and shiny and an awful lot of fun to play… we were shooting this film for 42 days so you've got to find much more than that, to be getting ourselves up at the hours we were getting up in the morning and still be fascinated".

"You've got to go beyond the colourful shininess of everything."

Indeed, Bale's ability to go beyond the physical and immerse himself in his roles has paid off time and again.

In the biopic The Fighter, another Russell project, he shed kilos to play down-and-out boxer and drug addict Dicky Eklund, who coaches half-brother Micky Ward (Mark Wahlberg) as Ward tries to turn professional.

The film picked up seven Oscar nominations in 2011, including for Best Picture and Best Director, and won Best Supporting Actor for Bale, who, typically, stayed in character throughout production, taking boxing lessons and speaking in Eklund's Bostonian accent even off-camera.

Although Bale has claimed he does not practise "method acting" - where performers immerse themselves by trying to understand and feel their characters' emotions - some have wondered whether the intensity he brings to his work might be a little unhealthy.

This is the man, after all, who said he had "a nervous breakdown and a panic attack" when he first put on his suit in the last Batman film, The Dark Knight Rises (2012), just because he was overcome with emotion, and that he threatened to pull out of the project as a result.

And as gifted as he is, the actor, who has a daughter, eight, with Sibi, his wife of 13 years, can reportedly be a difficult person on the set and off.

His former publicist of a decade published an unauthorised biography of him last year detailing his "explosive" temper, even with young fans, claiming that he has reduced little girls to tears after berating them for approaching him for autographs.

At press events, reporters are accustomed to seeing his face set in a scowl, his persona often appearing to match the character of whatever movie he is promoting. Given his predilection for gloomy subject matter, he is invariably less than cheerful.

This looks set to continue with his upcoming films, including Out Of The Furnace, a wrenching crime drama released in the United States this month, and director Ridley Scott's biblical epic Exodus, due out next year with Bale in the role of Moses.

Held up next to his other work, American Hustle is a bit of a departure because of its strong comedic and romantic overtones.

At the press conference in New York, Bale seems, accordingly, to be in an exceptionally good mood, jumping in to answer questions directed at the entire cast and cracking jokes that get some of the biggest laughs at the event. He proves so chatty that he even wanders off topic to volunteer this nugget: the involvement of 1960s singer Shirley Bassey in his creation of his Hustle character, who was based on the real-life convicted conman Mel Weinberg.

"When I spoke with Mel Weinberg, he said, 'Whenever there were bad times, I would imagine dancing with Shirley Bassey'," says Bale, beaming.

The affection he has for the character, a lovable rogue, is clear. But as detailed as his construction of a performance is, Bale says that he likes to leave some of the finer points deliberately vague.

"I never really like to define what exactly it is that I love about the character or the film.

"I do that intentionally because then you are discovering the character, discovering the piece as you keep going."