The Most Shocking Transformations Actors Have Undergone for a Role

Whether it's Chris Pratt getting ripped for Guardians of the Galaxy or Natalie Portman slimming down for Black Swan, actors transforming their bodies for a role isn't a new concept – but some tackle this challenge in healthier ways than others. Between gruelling training sessions and rigid eating plans, these celebs give a new meaning to method acting.

Back in his Parks and Rec days, Pratt wasn't known for being super fit. But all that changed once he started training for his leading role of Peter Quill in Guardians of the Galaxy.

Pratt reportedly hit the gym and changed his diet for the role. "I probably lost about 35lb in six weeks. I ran five or six miles a day. I ate leafy green salads and protein shakes. I cut out all alcohol. Trim, trim, trim," Pratt told Men's Health UK.

Christian Bale is no stranger to major transformations for films. He's lost weight, gained weight, and gotten super ripped for roles throughout his career.

But Bale's most notable transformation was for The Machinist in 2005. He reportedly went from 173 pounds to 110 pounds by living off of one can of tuna and an apple a day, plus coffee and water. For what it's worth, we do not recommend following this eating plan.

Moore got ripped to play Lieutenant Jordan O’Neil for the movie G.I. Jane, the first female Navy SEAL.

Moore trained with Gregory Joujon-Roche and Navy SEAL instructor Stephen Helvenston to get fit for the role. That meant hitting the gym to lift weights for two hours every day, as well as going on a six-mile run daily.

Not only did Hemsworth lose 30 pounds for In the Heart of the Sea, but he also bulked up afterwards to play Thor in Avengers: Age of Ultron.

Hemsworth's diet included a lot of chicken and fish, as well as daily protein smoothies to gain muscle. When training, Hemsworth opted for a slow tempo when lifting weights to maximize the time that his muscles were under tension.

McConaughey has always been relatively fit, but he went through a major weight loss transformation for his role as Ron Woodroof in Dallas Buyers Club, a man diagnosed with HIV/AIDS in the '80s.

How did he drop 47 pounds? "I'm doing cardio but I'll tell you what, the more I've learned is—and I think it comes with age too—is it's 90 percent diet," McConaughey told E! Online. McConaughey said he met with a nutritionist to lose the weight in the healthiest way possible over the course of four months.

To play Bridget in Bridget Jone's Diary in 2001, Zellweger went from a size 4 to a size 14.

She gained 30 pounds to play the role (and did the same for the sequel in 2004, too) by reportedly consuming 3,800 calories a day, nearly twice the recommended 2,000 for a woman her age at the time.

Leto lost weight for Dallas Buyers Club like his castmate McConaughey, but he also put on weight for Chapter 27, where he played John Lennon's killer.

Leto told New York Daily News of gaining 60 pounds: "I gorged and force-fed myself. It was important to make that transformation because I thought his physical representation of himself was an indication of who he was. And it changed everything about who I was—the way I walked, the way I talked, the way I felt about myself, the way people treated me."

Hathaway lost 25 pounds and shaved her head for the role of Fantine, a prostitute dying of tuberculosis, for Les Misérables in 2012.

She lost the first 10 pounds with a cleanse and another 15 by eating just two thin squares of dried oatmeal paste each day, according to Vogue: "I had to be obsessive about it—the idea was to look near death." Again, we do not recommend this weight loss method.

Reynolds trained and dieted to gain 25 pounds of muscle for Blade: Trinity back in 2004—which was a far cry from his routine at the time: "I was pretty unhealthy. I didn't care what I ate or what I drank," he told Muscle and Fitness.

But after three months of working out six days a week and following a 3,200-calorie daily diet, he gained 25 pounds. "That time changed my life because it taught me you can actually do things that were previously impossible," he told Muscle and Fitness.

Rapper 50 Cent is known for being pretty ripped, but he slimmed down and lost weight for his role as a cancer patient in Things Fall Apart.

He went from 214 pounds to only 160 pounds in nine weeks with a strict liquid diet. "I had to discipline myself not...to actually have myself be in the physical state to convey the energy I felt. It's a passion project for me," he told The Associated Press (via The Huffington Post).

For her role as a delusional ballerina in Black Swan, which ultimately earned Portman the Best Actress award at the 2011 Oscars, the actress slimmed down drastically.

Portman reportedly dropped 20 pounds for the role. "I was barely eating, I was working 16 hours a day. I was almost method acting without intending to. I do wonder now how people can do this kind of role when they have a family," she told Daily Mail.

Kunis dropped 20 pounds, just like Portman, for her role in Black Swan and ended up at a mere 95 pounds for the film.

"I had no shape, no boobs, no ass," Kunis told E! Online. "All you saw was bone. I was like, this looks gross." She says it took her five months to lose the weight, but just five days to put it back on.

Gyllenhaal gained 15 pounds of muscle to play a boxer in Southpaw. How did he do it? He worked out for six hours a day for six months.

Director Antoine Fuqua told Deadline, "We literally turned him into a beast. Jake, my god, he's a very electric, powerful fighter in this movie. He's so committed and gives his heart. The word is sacrifice."

Hanks had to gain 50 pounds before filming started on Cast Away to look like a middle-aged man, then production took a year off so he could drop the weight for the second half of the film.

Hanks didn't shave or cut his hair four months and lost a total of 55 pounds. He ate mostly crab, fish, vegetables, some fruits, coconut milk, and water.

Theron gained 30 pounds to play Aileen in Monster, and she definitely indulged in some donuts to put on the weight.

Theron told Spliced Wire that the goal of gaining weight was to get more in tune with her character: "It wasn't about getting fat. Aileen wasn't fat. Aileen carried scars on her body from her lifestyle, and if I'd gone to make this movie with my body—physically I'm very athletic—I don't know that I would have felt the things Aileen felt with her body."

Hardy bulked up in just five weeks to play Charles Bronson, Britain's most dangerous criminal, in Bronson.

Hardy started by hitting the gym hard and eating more calories. "I put on about 7 lbs a week—with no steroids. In the end I'd put on about 2 and a half stone by eating chicken and rice, which was my staple diet throughout the day. Then I'd have a pizza, Häagen-Dazs and Coca-Cola: So not good stuff, but I had to put weight on," he told Ask Men.

Okay, so Efron was always pretty buff, but he got insanely shredded for Baywatch.

Efron reportedly gave up all sugars and carbs and hit the gym three times a day for his role. "Patrick pushed me to my 'functional' limits with a very multifaceted style: strength, explosiveness, fast paced, calculated, diverse and gut-wrenching workouts. It was fun…you never know what he's going to throw at you the next day," he told E! News.

Another actor known for his method acting skills, Norton went from scrawny to built for his role as a former neo-Nazi who was recently released from prison in American History X.

Norton's diet consisted of a lot of protein and his coach, Anthony Krotes, focused on weight training with heavy weight and lower repetitions to get him to gain 30 pounds of definition and muscle.

Hill has been through some weight loss and fitness transformations throughout the years, including for his role in Netflix's Maniac in which he plays a man struggling with disputed schizophrenia.

His trick? "I wanted to get in better shape, so I called Channing Tatum and said, 'Hey, if I ate less and go to a trainer, will I get in better shape?'" Hill said on the The Tonight Show. So that's what he did.

To squeeze into her tight, tight corset for Cinderella, James went on a cleanse to drop weight, mostly to help her feel comfortable on set.

"When [the corset] was on, we would be on continuous days, so we wouldn't stop for lunch…you'd be sort of eating on the move. In that case, I couldn't untie the corset," she told E! News. "If you ate [solid] food, it didn't really digest properly, and I'd be burping all afternoon in [costar Richard Madden]'s face, and it was just really sort of unpleasant. I'd have soup so that I could still eat, but it wouldn't get stuck."