20 Actors Who Dramatically Changed Their Looks For Movies

Gyllenhaal really went all out to get into the mind of his deranged, career-hungry freelancer journalist.

The actor told Variety he didn't take on any special diet. Instead, he just stopped eating.

“I would try to eat as few calories as possible. I knew if I was hungry that I was in the right spot. Physically, it showed itself, but chemically and mentally, I think it was even a more fascinating journey. It became a struggle for me.”

Gyllenhaal added that he would often go on 15 mile runs from his home to the film's set.

In addition, his co-star Riz Ahmed claimed the star would chew flavored gum to trick his mind into believing he was eating a meal.

Pratt said he ditched beer to take on the role of Peter Quill in Marvel's hit. He also divulged his workout routine with a personal trainer and nutritionist to Men's Fitness.

It consisted of running, swimming, boxing, kickboxing, a triathlon, and consuming 4,000 calories a day.

"I actually lost weight by eating more food, but eating the right food, eating healthy foods, and so when I was done with the movie my body hadn't been in starvation mode," Pratt told People magazine.

Portman was on a carrots and almond diet, working five to eight hours a day for a year to slim her already trim figure down for the lead role in Darren Aronofsky's "Black Swan."

The 33-year-old actress revealed the extent of her preparation for the role to Entertainment Weekly:

"There were some nights that I thought I literally was going to die," Portman told EW. "It was the first time I understood how you could get so wrapped up in a role that it could sort of take you down."

After filming ended, the singer quickly returned to carbs. She announced a pregnancy with now husband, choreographer, Benjamin Millepied, who she met on set.

Though Portman is often cited as shrinking to an alarmingly small size for "Black Swan," Kunis did the same for her role in the Oscar-winning film, slimming down to 98 pounds.

Kunis was pretty vocal about her dismay with her shapeless body:

"I could see why this industry is so f----d up, because... I would literally look at myself in the mirror and I was like: 'Oh my God! I had no shape, no boobs, no a--...,'" she said. "All you saw was the bone. I was like 'this looks gross.'"

After filming, the actress binged out at a Panda Express in JFK airport and an "In and Out" after landing in Los Angeles. Kunis joked, "It took me five months to lose 20 pounds, and it took me hours to gain it back!"

Anne Hathaway shaved her head and dropped 16 pounds on a detox diet for "Les Miserables."

"This diet makes me break out, so I love that," Hathaway joked to Allure. "Nothing like living on hummus and radishes and then be all, 'And I got a pimple. Yeah!'"

The actress also told "Chelsea Lately" she became a vegetarian for "The Dark Knight Rises," living off of kale and dust for training.

Some people didn't believe Hardy bulked up enough to play villain Bane in "The Dark Knight Rises." In an interview with Total Film, the actor revealed his initial plan to get his weight up to 198 lbs.

Before the film's release, many fans were slightly displeased. In the comics and animated series, Bane's muscles are overexaggerated. He's able to lift 1,500 lbs.

Hardy later told CineMovie he got up to 190 lbs and defended his weight gain to fans:

"I’m at 190[lbs]. Bat-fans want me to be over 220lbs. 400lbs. I’m like dude! Batman is like Superman, Spider-Man — he belongs to so many people. So many people love him. He belongs to them, and when you step into that kind of character, you are going to fail. And be judged. I’m human, and I do read things. I read the comments, and I cry. I can’t cry for everybody. I just give them a job, and be the best that I can be. Just trust me. I trust Nolan."

Christian Bale wasn't even asked by director Brad Anderson of "The Machinist" to drop to a mere 122 pounds for the film. He told the BBC he wanted to do it all on his own.

"I was intrigued by a perverse nature of mine just to see if I can go beyond what I've been told is actually safe and OK, and see if I could push the limits," Bale said.

Bale's daily diet consisted of consuming vitamins, running, and eating an apple and can of tuna a day.

He then gained nearly 100 pounds, getting back up to 220 pounds in about five months to play the Caped Crusader in "Batman Begins."

"I will adjust for what is needed," Bale told People. "But only if I have quite an obsession about that role."

Bale estimated going from about 185 to 228 pounds for "American Hustle." The actor also shaved his head, and slouched enough to accidentally herniate a disc in his back.

The actor was so unrecognizable that co-star Robert De Niro had to ask who Bale was upon meeting him on set.

Damon not only packed on the pounds for his role as the vice president-turned CIA informant, Mark Whitacre, but he had fun doing it.

"I definitely got doughy," Damon told EW. "I started eating like crazy and drinking dark beer. Between meals on set, I'd eat a No. 1 Value Meal at McDonald's and then Doritos on top of it. It was absolute heaven."

Zellweger's weight has fluctuated back and forth for film roles. After gaining and then losing 20 lbs for "Bridget Jones's Diary" and "Chicago," the actress was eager to gain the weight back for the "Jones" sequel.

"I'm ready, willing and able," Zellweger told the London Times. "Bridget's a character I really identify with. I'll put the weight back on with pleasure."

Zellweger began eating 4,000 calories a day to gain the weight.

George Clooney didn't enjoy packing on the pounds for his role as a CIA operative in 2005's "Syriana."

"There was nothing fun about it," said Clooney. "There was not a moment that was fun about shooting this film. That's not a slap on the film or (the director Stephen) Gaghan. It's just that everybody has that year where you age a decade and this was that one for me."

Co-star Matt Damon even said Clooney was so distraught with his inability to exercise he became depressed.

Afterward, the actor dramatically lost the weight and more for his role in "Michael Clayton." Clooney lost so much weight that his publicist was forced to announce the star wasn't ill.

Charlize Theron told Guerrilla Traveler she ate junk food to gain weight for the prostitute-turned-serial killer in 2003's "Monster."

“I first began stuffing myself with Krispy Kreme doughnuts, but after a while I got sick of them,” Theron said. “I love potato chips, so that was a good thing for me. I’m a salty girl so I had my secret stash with me of potato chips at all times.”

Theron won the Best Actress Oscar for her performance.

After the film, the star slimmed down immediately for her next role in "Head in the Clouds."

Hanks has lost and gained weight for a few roles, but his 55 pound weight loss for 2000's "Castaway" was his most extreme diet.

Hanks told Entertainment Weekly what he missed most while shedding the pounds.

''Oh, those FFs, man. Those fries from France…," said Hanks. "The only thing I did not give up was coffee.... Nope, wasn't about to!"

Hanks previously gained 30 pounds for the role of Jimmy Dugan in 1992's "A League of Their Own" and subsequently lost 26 pounds to play AIDS-stricken Andrew Beckett in "Philadelphia."

Reynolds' trainer, Bobby Storm, told WebMD the star worked out 90-minutes every day for six-to-seven months to bulk up to 200 pounds.

"For a romantic comedy, he needs to shrink down a bit," said Storm. "For Blade and Green Lantern, he was 200 pounds and 8% body fat. For rom coms [romantic comedies], he’s about 180 and 11% body fat."

Reynolds told Men's Fitness he gained 25 pounds of muscle for "Blade Trinity" after adhering to a 3,200 calorie daily diet and doing six-day-a-week workouts for three months.

D'Onofrio holds the record for gaining the most weight for a role after he put on 70 pounds for Stanley Kubrick's 1987 film "Full Metal Jacket."

The actor also gained 45 pounds for the 2002 movie, "The Salton Sea."

Hillary Swank consumed 210 grams of protein every day for 90 days while training for "Million Dollar Baby."

"My training was two and a half hours of boxing and approximately an hour and a half to two hours lifting weights every day, six days a week," Swank told Movieweb.com. "The producers asked me to gain 10 pounds of muscle. I gained 19 pounds of muscle. I started at 110 and went to 129. I would drink my egg whites because I could never eat 8 to 12 egg whites in a sitting. It's just the worst thing ever."

Director Sir Richard Attenborough had been searching for an actor to play Gandhi for 20 years when he offered British actor Ben Kingsley the role.

Kingsley, whose father is of Indian descent, underwent extensive preparation for the role — reading biographies, studying photographs, shaving his head, and losing 20 pounds on Gandhi's very own vegetarian diet.

While talking about his role to the New York Times, Kingsley said:

''When I have totally immersed myself in the mechanical, logical preparation of a part, if I and my craft are totally bonded and fully exploited, something else in me is awakened and begins to inform my work..."

Talk about dedication.

In order to play the iconic boxer Jake LaMotta in "Raging Bull," Robert De Niro built muscle and trained with the legend himself to get the look of the boxer during his heyday. De Niro even fought in three different boxing matches in attempt to be as convincing as possible.

To portray LaMotta's later years, De Niro packed on almost 60 pounds of weight, a drastic body change that gave the actor rashes and breathing issues.

It paid off — De Niro picked up both a Golden Globe and Academy Award for his role in "Raging Bull."

Ridley Scott's 1997 film "G.I. Jane" cast Demi Moore as Lieutenant Jordan O'Neill, the first female Navy SEAL to undergo U.S. Navy Special Warfare Group training.

Moore worked with an ex-seal personal trainer, Scott Helvenston, to sustain the toll the film would take on her body. Her diet was a high-protein, high-calorie one restricted to protein including chicken breast and salmon and vegetables of spinach and broccoli. Moore and the rest of the cast participated in intense military training — everything from obstacle courses to push-ups and sit-ups.

Moore later spoke about her preparation, saying:

"I could have come in and asked to let the stunt woman do the obstacle course," Moore says. "But I felt I would have walked away having missed an opportunity experiencing, first-hand, what these people actually go through in training; it's the whole reason for doing this film in the first place."

And we can't forget Moore's iconic hair change — the actress actually buzzed off all her hair for the role.

The best part? Gosling never appeared in the 2009 film.

Gosling told The Hollywood Reporter Peter Jackson fired him when he showed up 60 pounds heavier to the set.

"I was 150 pounds when [Jackson] hired me, and I showed up on set 210 pounds," Gosling said. "We had a different idea of how the character should look. I really believed he should be 210 pounds. I was melting Haagen Dazs and drinking it when I was thirsty."

Gosling admitted he didn't think he looked great; however, he thought it was necessary for the role of a grieving father.

"I really believed in it. I was excited about it. I showed up, and they said, 'You look terrible.' And I said, 'I know! Isn't it great?' 'No, it's not. Go hit the treadmill' ... then I was fat and unemployed."

Jackson's wife, Fran Walsh, told a different story about the actor's insecurities for the role resulting in his ultimate departure from the role.

See what other stars changed their names for fame >