Jake Gyllenhaal shocked onlookers with his gaunt appearance at the 17th Annual Hollywood Film Awards on Monday night.
And while the 20lb weight loss was for his role as a freelance crime reporter who stumbles upon the dangerous underworld of Los Angeles in Nightcrawler, his new look is still alarming.
Gyllenhaal’s razor sharp cheekbones now protrude noticeably and the star insists he wanted his character Lou to be ‘literally and figuratively hungry’.
'I knew that [Lou] was literally and figuratively hungry, [so I got into the] mode where I was always a bit hungry,’ he told Us Weekly.
Jake, 32, added, ‘The movie takes place, in a land where I think there is a desert in a lot of ways, great opulence, and at the same time, great vastness and emptiness.’
‘I think [I've lost] probably a little over 20lbs , something like that,’ he told People.
Jake added, ‘It's not different than getting into character for anything. It's more about believing where you are and being present where you are. Who's to say what the process is? I have a strange one … but I love what I do.’
When asked his tips for losing weight, Jake said, ‘I just love this movie. That’s how I did it. There really was no technique.’
Before going to the Hollywood Film Awards ceremony at the Beverly Hilton in Beverly Hills on Monday, Gyllenhaal was spotted on the set of Nightcrawler displaying his shocking weight loss.
People Magazine’s Sexiest Man Alive 2009 was virtually unrecognisable as he shot scenes where his character was filming crime footage.
Dressed down in a light grey jacket and dark trousers, he and a colleague shot footage of an ambulance during a night scene.
His brown locks were long and combed back as though his character, Lou, not only doesn’t have time to eat but also had no time for a haircut either.
Nightcrawler, which began shooting on October 6, is set LA and also stars Bill Paxton and Rene Russo, who is wed to the film's director, Dan Gilroy.
Gyllenhaal, who is six feet tall, tends to alter his looks to suit the part.
No-one can forget Jake the hunky royal fugitive in 2010's Prince Of Persia: The Sands Of Time, a role that required him to bulk up considerably.
As Jake told Men's Fitness last year, he used the Parkour method of training that involves running and jumping between buildings or other outdoor obstacles.
Jake also relied on six small meals a day that were loaded with protein, beneficial carbohydrates and fats, and water.
'I got into shape so that I would be able to do those stunts,' Jake explained to The Arizona Republic at the time.
'I wanted to do those stunts and I wanted to not get injured when I did them and I wanted to be able to pull them off. The only way to do that would be to get in really good shape, like all the stunt guys around me. And I did that.'
He added: 'I don't think anybody expected there to be so much focus on the physical aspect.'