Some actors take their roles very seriously.
From Matthew McConaughey's 40-pound weight loss for "Dallas Buyers Club" to Bradley Cooper's 40-pound weight gain for "American Sniper," celebrities have the ability to transform their bodies in order to portray certain characters.
Here are 26 stars who took method acting to a whole other level:
Ben Affleck
Zack Snyder/Twitter
Movie: "Batman v Superman: Dawn of Justice" (2016)
Role: Batman, the Caped Crusader.
Weight Gain: Affleck's wife, Jennifer Garner, said he has been working out at least twice a day and that he’s currently sporting 17-inch biceps.
Role: Batman, the Caped Crusader.
Weight Gain: Affleck's wife, Jennifer Garner, said he has been working out at least twice a day and that he’s currently sporting 17-inch biceps.
Bradley Cooper
FameFlynet
Movie: "American Sniper" (2015)
Role: Navy SEAL Chris Kyle, the most lethal sniper in American military history with more than 150 confirmed kills.
Weight Gain:He reportedly gained 40 pounds and grew a beard to star in the film, based on a true story.
Role: Navy SEAL Chris Kyle, the most lethal sniper in American military history with more than 150 confirmed kills.
Weight Gain:He reportedly gained 40 pounds and grew a beard to star in the film, based on a true story.
Chris Hemsworth
FameFlynet
Movie: "Heart of the Sea" (2015)
Role: One of a few sailors who is lost at sea for 90 days after their ship gets struck by a whale and sinks. (Think "Moby Dick.")
Weight Loss: After losing 30 pounds for "Rush," Hemsworth crash dieted for Ron Howard's latest movie by eating only 500 calories-a-day.
Role: One of a few sailors who is lost at sea for 90 days after their ship gets struck by a whale and sinks. (Think "Moby Dick.")
Weight Loss: After losing 30 pounds for "Rush," Hemsworth crash dieted for Ron Howard's latest movie by eating only 500 calories-a-day.
Advertisement
Chris Pratt
Chris Pratt/Instagram
Movie: "Guardians of the Galaxy" (2014)
Role: American pilot named Peter Quill who finds himself the object of a manhunt after stealing an orb coveted by the villainous Ronan.
Weight Loss: After weighing in at 300 pounds for "Delivery Man," Pratt dropped over 50 pounds for the Marvel movie.
Role: American pilot named Peter Quill who finds himself the object of a manhunt after stealing an orb coveted by the villainous Ronan.
Weight Loss: After weighing in at 300 pounds for "Delivery Man," Pratt dropped over 50 pounds for the Marvel movie.
Matthew McConaughey
Focus Features
Movie: "Dallas Buyers Club" (2013)
Role: Ron Woodruff, a Texas rodeo cowboy who is diagnosed with HIV and given 30 days to live.
Weight Loss: More than 40 pounds, eliminated by cardio and diet.
Role: Ron Woodruff, a Texas rodeo cowboy who is diagnosed with HIV and given 30 days to live.
Weight Loss: More than 40 pounds, eliminated by cardio and diet.
Jared Leto
FameFlynet
Movie: "Dallas Buyers Club" (2013)
Role: Rayon, an HIV-positive transgender woman.
Weight Loss: “I stopped eating,” Leto told TheWrap of his diet. “It was 30 or 40 pounds. After a while I stopped counting.”
Role: Rayon, an HIV-positive transgender woman.
Weight Loss: “I stopped eating,” Leto told TheWrap of his diet. “It was 30 or 40 pounds. After a while I stopped counting.”
Advertisement
Anne Hathaway
Universal Pictures
Movie: "Les Misérables" (2012)
Role: Tuberculosis-afflicted prostitute Fantine.
Weight Loss: Hathaway lost 25 pounds, 10 before shooting and 15 during. She won the Best Supporting Actress Oscar for the role in 2013.
Role: Tuberculosis-afflicted prostitute Fantine.
Weight Loss: Hathaway lost 25 pounds, 10 before shooting and 15 during. She won the Best Supporting Actress Oscar for the role in 2013.
Matthew Fox
Summit Entertainment
Movie: "Alex Cross" (2012)
Role: Picasso, a professional assassin who participates in an underground ultimate-fighting ring.
Weight Loss: "It was circuit training until I wanted to puke," Fox said of the 40 pounds he shed to play the chronically fit serial killer.
Role: Picasso, a professional assassin who participates in an underground ultimate-fighting ring.
Weight Loss: "It was circuit training until I wanted to puke," Fox said of the 40 pounds he shed to play the chronically fit serial killer.
Chris Evans
Marvel Entertainment
Movie: "Captain America: The First Avenger" (2011)
Role: Marvel's iconic superhero, Captain America.
Weight Gain: The 6-foot-3 actor was required to gain over 20 pounds of pure muscle in order to play the action hero.
Role: Marvel's iconic superhero, Captain America.
Weight Gain: The 6-foot-3 actor was required to gain over 20 pounds of pure muscle in order to play the action hero.
Advertisement
Seth Rogen
Columbia Pictures
Movie: "The Green Hornet" (2011)
Role: Britt Reid aka The Green Hornet.
Weight Loss: Rogen shed 40 pounds with the help of a personal trainer.
Role: Britt Reid aka The Green Hornet.
Weight Loss: Rogen shed 40 pounds with the help of a personal trainer.
Curtis "50 Cent" Jackson
Twitter
Movie: "All Things Fall Apart" (2011)
Role: Deon, a celebrated football player battling cancer.
Weight Loss:He lost more than 50 pounds.
Role: Deon, a celebrated football player battling cancer.
Weight Loss:He lost more than 50 pounds.
Chris Hemsworth
Getty
Movie: "Thor" (2011)
Role: Marvel's superhero Thor, the god of Thunder.
Weight Gain:Hemsworth gained 20 pounds of muscle in order to play the beloved hero.
Role: Marvel's superhero Thor, the god of Thunder.
Weight Gain:Hemsworth gained 20 pounds of muscle in order to play the beloved hero.
Advertisement
Natalie Portman
Fox Searchlight
Movie: "Black Swan" (2010)
Role: A ballet dancer who slowly loses her mind after nabbing the lead in "Swan Lake."
Weight Loss: Portman lost 20 pounds to play a ballerina, with director Darren Aronofsky telling Access Hollywood, "At a certain point I looked at [Natalie's] back and she was so skinny and so cut. I was like, 'Natalie, start eating.' I made sure she had a bunch of food in her trailer. She took [the role] very seriously. These dancers get really, really skinny.”
Role: A ballet dancer who slowly loses her mind after nabbing the lead in "Swan Lake."
Weight Loss: Portman lost 20 pounds to play a ballerina, with director Darren Aronofsky telling Access Hollywood, "At a certain point I looked at [Natalie's] back and she was so skinny and so cut. I was like, 'Natalie, start eating.' I made sure she had a bunch of food in her trailer. She took [the role] very seriously. These dancers get really, really skinny.”
Amy Adams
Relativity Media
Movie: "The Fighter" (2010)
Role: Bartending wife of Mickey Ward, Charlene Fleming.
Weight Gain: "[David O. Russell] said, 'I want you to look like a girl who drinks beer,'" Adams told Parade magazine. So, she did just that.
Role: Bartending wife of Mickey Ward, Charlene Fleming.
Weight Gain: "[David O. Russell] said, 'I want you to look like a girl who drinks beer,'" Adams told Parade magazine. So, she did just that.
Christian Bale
Paramount Pictures
Movie: "The Fighter" (2010)
Role: Professional boxer Dicky Eklund, who suffered from a crack addiction.
Weight Loss: "I never got on a scale. I didn't want it to be about the numbers; I wanted it to be about the look," Bale told "Access Hollywood."
Role: Professional boxer Dicky Eklund, who suffered from a crack addiction.
Weight Loss: "I never got on a scale. I didn't want it to be about the numbers; I wanted it to be about the look," Bale told "Access Hollywood."
Advertisement
Matt Damon
Warner Bros.
Movie: "The Informant!" (2009)
Role: Archer Daniels Midland executive Mark Whitacre.
Weight Gain:Damon gained 30 pounds by eating McDonald's meals, Doritos and beer.
Role: Archer Daniels Midland executive Mark Whitacre.
Weight Gain:Damon gained 30 pounds by eating McDonald's meals, Doritos and beer.
Colin Farrell
Entertainment One
Movie: "Triage" or "Shell Shock" (2009)
Role: A photojournalist with PTSD.
Weight Loss: Farrell lost 44 pounds, thanks to a diet of only tuna, coffee and diet soda.
Role: A photojournalist with PTSD.
Weight Loss: Farrell lost 44 pounds, thanks to a diet of only tuna, coffee and diet soda.
Michael Fassbender
Icon Film Distribution
Movie: "Hunger" (2008)
Role: Bobby Sands, who led a Provisional Irish Republican Army hunger strike in 1981.
Weight Loss: Fassbender lost 42 pounds after adopting a diet of 600 calories a day, heavy on nuts and berries.
Role: Bobby Sands, who led a Provisional Irish Republican Army hunger strike in 1981.
Weight Loss: Fassbender lost 42 pounds after adopting a diet of 600 calories a day, heavy on nuts and berries.
Advertisement
George Clooney
Warner Bros.
Movie: "Syriana" (2005)
Role: CIA agent Robert Baer.
Weight Gain: 30 pounds, with the help of bowls and bowls of pasta
Role: CIA agent Robert Baer.
Weight Gain: 30 pounds, with the help of bowls and bowls of pasta
Hilary Swank
Warner Bros.
Movie: "Million Dollar Baby" (2004)
Role: Maggie Fitzgerald, who becomes a professional boxer.
Weight Gain: She gained 19 pounds of muscle and reportedly ate every 90 minutes and consumed 210 grams of protein daily.
Role: Maggie Fitzgerald, who becomes a professional boxer.
Weight Gain: She gained 19 pounds of muscle and reportedly ate every 90 minutes and consumed 210 grams of protein daily.
Christian Bale
Paramount Classics
Movie: "The Machinist" (2004)
Role: A machinist with intense insomnia.
Weight Loss: Bale dropped 63 pounds. "I had what could be called a kind of stupid feeling of invincibility, like, 'Oh I can do it. I can manage it,'" Bale said.
Role: A machinist with intense insomnia.
Weight Loss: Bale dropped 63 pounds. "I had what could be called a kind of stupid feeling of invincibility, like, 'Oh I can do it. I can manage it,'" Bale said.
Advertisement
Charlize Theron
Newmarket Films
Movie: "Monster" (2003)
Role: Prostitute and serial killer, Aileen Wuornos.
Weight Gain: The actress gained 30 pounds (by eating doughnuts) and was almost unrecognizable.
Role: Prostitute and serial killer, Aileen Wuornos.
Weight Gain: The actress gained 30 pounds (by eating doughnuts) and was almost unrecognizable.
Renee Zellweger
Universal Pictures
Movie: "Bridget Jones's Diary" (2001)
Role: Bridget Jones.
Weight Gain: Zellweger packed on between 20 to 30 pounds to play the leading lady in "Bridget Jones's Diary" and its 2004 sequel, "Bridget Jones's Diary: The Edge of Reason." She credits a lot of "fattening foods."
Role: Bridget Jones.
Weight Gain: Zellweger packed on between 20 to 30 pounds to play the leading lady in "Bridget Jones's Diary" and its 2004 sequel, "Bridget Jones's Diary: The Edge of Reason." She credits a lot of "fattening foods."
Tom Hanks
20th Century Fox and Dreamworks
Movie: "Cast Away" (2000)
Role: Chuck Noland, a systems analyst whose airplane crashes, leaving him alone in the Pacific Ocean.
Weight Loss: Hanks gained 50 pounds to portray the pudgy Chuck and then had to shed the weight to depict his growing state of emaciation while stranded.
Role: Chuck Noland, a systems analyst whose airplane crashes, leaving him alone in the Pacific Ocean.
Weight Loss: Hanks gained 50 pounds to portray the pudgy Chuck and then had to shed the weight to depict his growing state of emaciation while stranded.
Advertisement
Matt Damon
20th Century Fox
Movie: "Courage Under Fire" (1996)
Role: An Army medic who goes AWOL.
Weight Loss: 40 pounds, which was reportedly shed via daily running and a diet of chicken breast, egg whites and one plain baked potato per day along with large amounts of coffee and cigarettes.
Role: An Army medic who goes AWOL.
Weight Loss: 40 pounds, which was reportedly shed via daily running and a diet of chicken breast, egg whites and one plain baked potato per day along with large amounts of coffee and cigarettes.
Tom Hanks
TriStar Pictures
Movie: "Philadelphia" (1993)
Role: Andrew Beckett, a lawyer dying of AIDS.
Weight loss: Hanks lost nearly 30 pounds for the role.
Role: Andrew Beckett, a lawyer dying of AIDS.
Weight loss: Hanks lost nearly 30 pounds for the role.