35+ Actors Who Underwent Dramatic Transformations For A Role

As actors themselves know however, it's a job that takes incredible amounts of skill and dedication. It often goes far beyond slipping into character to deliver a few lines here and there, wearing some make-up or perhaps a fake moustache.

In The Machinist (2004), Christian Bale plays the role of Trevor Reznik, a machinist with severe insomnia. The lack of sleep leads to severe weight loss, so Reznik becomes extremely thin. To be fit for the character Bale needed to look drastically thin, so he had to lose a lot of weight. He went from from 173 pounds to 110 pounds. To lose these 63 pounds, the actor followed a draconian diet: for almost four months he ate only one can of tuna fish and one apple per day.

This type of diet is a very low calorie diet, ensuring only around 260 calories a day. There are 194 calories in one can (6.5 ounce) of tuna in water, and one medium size apple (about 150 g) has 80 calories. The “menu” was completed with black coffee and water.

Besides the extremely low calorie intake, the foods chosen for this diet are, by themselves, metabolism boosters. Due to the caffeine content, coffee increases the metabolism. The apples are high in sugar and pectin (a soluble fiber) which dampens down the appetite.

To lose weight faster, Christian Bale exercised hard. The star’s exercise regime included intensive cardio workouts and intensive resistance/weight training workouts.

The lengths to which Leto went for his latest role might seem just a tad extreme. To play John Lennon's assassin, Mark David Chapman, in J.P. Schaefer's film, "Chapter 27," Leto packed 67 pounds onto his lanky frame to better approximate the killer's doughy physique. By the end of filming, the extra weight had taken such a toll that he could no longer walk to the set. It's easily his most dramatic transformation to date.

"I'm not sure it was the wisest choice," he admits. "A friend of mine was recently going to gain weight for a film, and I did my best to talk him out of it. Just because you can lose the weight doesn't mean the impact it had on you isn't there anymore."

The abruptness of Leto's weight gain gave him gout and a doctor's recommendation to take Lipitor. But Leto says slipping into Chapman's skin was the best way to understand him. "The script didn't say, 'Page 1: You gain 67 pounds, and you're miserable for two months.' But as I started to research, I realized that the physical representation of this guy had so much to do with who he was."

Gyllenhaal gained 15lbs of muscle to play a middleweight boxer in the movie ‘Southpaw,’ by working out six hours a day for six months, including at the Las Vegas gym of Floyd Mayweather, the champion boxer.

Southpaw’s director, Antoine Fuqua said that “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.”

He was spending so much time in the gym and was so committed to the role that his relationship with Alyssa Miller ended. “The amount of time you have to put into it, the sacrifice that you put into your body, it's not something that you're eager to do again. It's a huge commitment.” Gyllenhaal said about his gruelling preparation for the role.

An astounding aspect of the movie 'Dallas Buyers Club' is actor Matthew McConaughey’s remarkable weight loss. He dropped over 40lbs for the based-on-true-events story of AIDS patient Ron Woodroof, a man who challenges the US government to bring unapproved medication to other sufferers. McConaughey explained how, despite concerns from others over the potential negative impact on his health, he found he had plenty of energy, mentally at least – to complete the unremitting 25-day shoot.

“The amount of energy I lost from the neck down, I gained from the neck up,” he says. “I’ve seen people dying from HIV and cancer, and the last thing to go is the neck up. They are just savage from the neck up – their body is withering away but they are like a starving baby eagle in the nest waiting for the worm. So during filming, I had plenty of energy. I needed three hours less sleep a night.”

“I did it in as healthy a way as I found possible,” he says.

“I met with a nutritionist. I gave myself four months to lose the weight. I had my programmed meals, lost 3.5lb a week - like clockwork - and got down to my desired weight.’’

Of all the actors who had to pack on mass for a movie, few in recent memory have taken to the task with such zeal, and notable success, as Chris Hemsworth when he landed the part of Thor.

For the first film, Hemsworth hit the gym with trainer and former Navy SEAL Duffy Gaver, who applied an old-school bodybuilding approach—with careful attention given to Hemsworth’s arms and shoulders. Thor, after all, often appears sleeveless, but rarely shirtless. All told, Hemsworth gained 20 pounds, laying the foundation for a physique he’s maintained at or close to peak condition for Thor’s recurring role in The Avengers and the solo sequel, Thor: The Dark World.

Hemsworth was a model of consistency, and the physique he built has made “Chris Hemsworth Workout” the top search suggestion when you punch the actor’s name into Google.

“People see Chris and they think he was on steroids, but he didn’t touch a single substance,” Gaver says. “It was just red meat, heavy weights and some protein powder. He crushed every single workout. He simply decided to look like Thor.”

The 47-year-old Oscar winner transformed his appearance to play gold prospector Kenny Wells, adding 47 lbs. to his typically athletic frame.

McConaughey famously lost 38 lbs. for ‘Dallas Buyers Club,’ but ‘Gold’ marked the first time he'd ever gained weight for a role without adding muscle mass. "I haven't ever done that. I said, 'McConaughey, you have six months to say yes to whatever you want to eat and whatever you want to drink. Whenever.' That was fun," he says. "The only thing that gets tiring is the thought of quitting. It was fortunate that I was like, 'Oh, this is also my job, so let's go—all green lights.'"

Surprisingly, packing on the pounds was much easier than he'd anticipated.

"My favorite food is cheeseburgers, so I was eating cheeseburgers all the time. I was making cheeseburgers. I was trying out all these fast food restaurants that I've never had, or I've only had one time," he explains. "Not that much sweets. Cheeseburgers and beer will do the trick."

In addition to eating "whatever I wanted," McConaughey stopped working out altogether. "I wouldn't even take the stairs to the second floor," he says. "That would be too much exercise."

McConaughey's three children with wife Camila Alves "loved" their dad's gluttonous phase. "I was Captain Fun—that was my nickname around the house, because I was saying 'yes' to everything. I was a really fun dad for that six months because I was like, 'No, pizza night's not just Friday night—it's Tuesday night; it's Wednesday morning.'"

The Queens rapper 50 Cent shed nearly 60 pounds to play a football player who has been diagnosed with cancer in the Mario Van Peebles film, ‘Things Fall Apart.’

Fitty, who normally tips the scales at 214 pounds, released a photo of himself at a frail 160lbs.

The rapper says he lost the weight by going on a liquid diet and spending three hours a day on the treadmill for nine weeks.

"I was starving," he said. The 34-year-old, whose real name is Curtis Jackson, also removed his arm tattoos for ‘Things Fall Apart.’ "It cuts down on the amount of time I have to spend in makeup covering them up.”

Jared Leto lost an astonishing 40 pounds to play a transsexual with AIDS in ‘Dallas Buyers Club,’ alongside his co-star Matthew McConaughey whose weight loss is described above.

How did he do it? “I stopped eating, it wasn’t an easy thing to do. It was 30 or 40 pounds. After a while I stopped counting.”

Ultimately his weight dropped to 114 pounds to play Rayon, a transsexual with the HIV virus and then AIDS. Losing that much weight changed him, he said. “It changes the way you walk, the way you sit, the way you think,” he said.

After his extreme weight gain for the movie ‘Chapter 27,’also described above, it’s clear that Leto is incredibly dedicated to his art. The hard work and dedication paid off as ‘Dallas Buyers Club’ won a plethora of awards, and he bagged an Oscar for Best Supporting Actor for his role in the film.

Jonah Hill’s weight has fluctuated back and forth from lean to full-figured over the past few years. He slimmed down for the action-comedy 22 Jump Street in 2014, but gained 40lbs for his role in War Dogs in 2016 to play real-life arms dealer Efraim Diveroli.

These days Hill is a much slimmer figure in general and appears to have put his weight battles behind him. His physique looks almost unrecognizable compared to his burly figure in films like Superbad, The Sitter, and This Is the End, making for quite the body transformation.

The actor had to put on 50 lbs (23 kg) during pre-production to make him look like a middle-aged man. When Tom Hanks was in this shape, they shot the parts of the film before the island scenes, and then took a year off to let Tom lose weight to impersonate a real cast away. He didn’t shave or cut his hair for weeks and shed 55lb in four months with a diet and a tough exercise regime.

“The idea of looking at four months of constant vigilance as far as what I ate, as well as two hours a day in the gym doing nothing but a monotonous kind of work-out was formidable. You have to power yourself through it almost by some sort of meditation trickery. It’s not glamorous,” Hanks said.

His diet consisted mainly of: crab, fish, vegetables, very little carbohydrate from fruits, coconut milk and water. When Hanks felt hungry, he ate large amounts of vegetables. This allowed him to consume natural food without having to go hungry between meals. This diet later became famously known as the Castaway Diet.

“Three or four hours a day of just consistent, ass-kicking hard work.” Is how Chris Pratt, star of the film 'Guardians of the Galaxy,' ditched 60 pounds in six months. Pratt, who is most known for playing Andy Dwyer in the sitcom 'Parks and Recreation,' was in the neighborhood of 300 pounds when he auditioned for the Marvel movie.

Marvel would pair Pratt with personal trainer Duffy Gaver and nutritionist Phil Goglia. Goglia revamped Pratt’s diet, hiking his caloric intake to 4,000 calories a day and adding lots and lots of water—one for every pound he weighed. “I was peeing all day long, every day. That part was a nightmare,” Pratt said.

Admittedly, Pratt had started gaining weight purposely for his Parks and Recreation character, but now he's committed to remaining ripped: “It gave me a sense of absolute control,” he said.

The lengths to which Leto went for his latest role might seem just a tad extreme. To play John Lennon's assassin, Mark David Chapman, in J.P. Schaefer's film, "Chapter 27," Leto packed 67 pounds onto his lanky frame to better approximate the killer's doughy physique. By the end of filming, the extra weight had taken such a toll that he could no longer walk to the set. It's easily his most dramatic transformation to date.

"I'm not sure it was the wisest choice," he admits. "A friend of mine was recently going to gain weight for a film, and I did my best to talk him out of it. Just because you can lose the weight doesn't mean the impact it had on you isn't there anymore."

The abruptness of Leto's weight gain gave him gout and a doctor's recommendation to take Lipitor. But Leto says slipping into Chapman's skin was the best way to understand him. "The script didn't say, 'Page 1: You gain 67 pounds, and you're miserable for two months.' But as I started to research, I realized that the physical representation of this guy had so much to do with who he was."

Natalie Portman endured a punishing schedule for her role as a ballerina in Black Swan, which left her fearing she was going to die.

The waif-like 29-year-old lost 20lb for the role, eating little more than carrots and almonds on a punishing diet, and spent eight hours a day in rehearsals. Ms. Portman, who won an Oscar for her portrayal of the desperately ambitious, perfectionist dancer, said: "There were some nights that I thought I literally was going to die."

The film left her physically and emotionally drained: "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."

The actress, who dislocated a rib during rehearsals, said recently: "All dancers are always dancing with an extreme injury. Not just a sore muscle, they're dancing on a sprained ankle or with a twisted neck or something. You'll see them do incredible stuff and then limp off stage, straight to a bucket of ice. Part of the art is hiding all the pain."

The film received mixed reviews from ballerinas. Racheal Prince, of Ballet British Columbia, said she thought Ms. Portman's character was exaggerated. "She's anorexic, bulimic, crazy," the 26-year-old dancer said. "I'm sure every dancer struggles with little things here and there, but for one girl to struggle with every single problem out there, it just makes us look crazy."

For the Bridget Jones movies, Zellweger ate what she wanted, packed on 30 lbs. and earned an Oscar nomination. The bad part of playing Jones? The aftermath—losing all those, as Bridget would say, “wobbly bits.”

When the cameras were off, Zellweger chatted up locals and ate burgers with the crew. Still, maintaining her expanded waistline—she went from size 4 to a 14—required focus. “I was afraid those pounds would disappear because we worked so much,” says Zellweger, whose assistant kept her supplied with snacks. It wasn’t always enough. “In one scene they had to pad out her bottom because it wasn’t large enough,” says a crew member. “I was expecting her to be huge, and she just wasn’t.”

After filming ended, Zellweger cut her 4,000-calorie-a-day diet, began exercising and caused a press frenzy with her super-slim frame. Bridget producer Eric Fellner says he doesn’t understand all the attention. “She puts weight on for the role; she doesn’t take it off to be Renée,” he says. “She’s naturally very tiny,” concurs Cameron Silver, owner of L.A.’s vintage boutique Decades, a favourite of the actress’s. The weight gain, Fellner points out, was just part of the job. “She’s very professional, whether we had her falling out of an airplane or covered in pig poo.”

Emile Hirsch had to undergo dramatic weight loss for the movie ‘Into The Wild,’ to accurately portray Chris McCandless, a man who ventured into the Alaskan Wilderness and eventually starved to death.

“I weighed about 156 pounds when I got the part, and I weighed 130 pounds throughout most of the film, so I lost the 26 pounds to get in shape for the film,” he said. “And then I went down to 115 pounds for the weight loss in the Alaska segment. So it was like two stages of weight loss.”

How did he do it? “So it was a lot of running and being very hungry and dreaming of candy all the time. It’s funny because normally, I’m not a big chocolate bar eater. But, that was really what I wanted more than anything when I was at my most hungry. It was like, Steak? No. Like a Take 5 Candy Bar? That was like the Ideal.”

Transforming into Lieutenant Jordan O’Neil, the first female Navy SEAL, for the movie G.I. Jane was not an easy task. The Demi Moore workout and diet are what she used to become G.I Jane, and included real Navy SEAL training, combined with a lot of strength, cardio, and martial arts.

For G.I. Jane, Moore’s workout would start at 4:00 am, in order to finish before filming started. Living in New York City at the time, she had multiple security guards following her while running in Central Park.

She used celebrity trainer Gregory Joujon-Roche for getting in shape, and Navy SEAL instructor Stephen Helvenston to gain that visceral, Navy SEAL mindset while filming. To immerse herself in the role she shaved her head, did Navy SEAL obstacle courses and other military-type exercises such as underwater running, one arm pushups and sit-ups in the mud.

Fox shed nearly a fifth of his bodyweight to play the emaciated villain in the heavy-duty thriller ‘Alex Cross.’ “When I took on the role in this film I said I wanted to radically change the way that I look, that’s the only way that I would buy me as that character.” It’s a bodily transformation equal to the jailhouse superman that Robert De Niro achieved in Cape Fear and a metamorphosis not dissimilar to Christian Bale’s skeletal appearance in The Machinist.

But the former Lost star wanted to change his body in a more unusual way: he wanted to do it healthily. Whereas Bale simply jacked up his cardio routine and put himself on starvation rations, Fox was determined to do it in such a way that he would have sufficient attention to work hard, think straight and generally be a functioning employee, husband and father.

“We wanted to build a physique that looked natural to the character – not just a gym body,” says Simon Waterson, the trainer who prepares Daniel Craig for his Bond roles and is recognised as the smartest cinematic body-transformer in the business. “Matthew knew exactly what he wanted to look like for the role: menacing and a little psychotic.

“We couldn’t put him on an extreme, low-calorie diet,” says Waterson. “It would have starved his brain of sugar, and his thought processes would have slowed right down. I couldn’t sap him of the energy he needed to work, so everything had to be very balanced.”

In other words, the rapid fat-zapping he undertook may have had crazy results, but it didn’t rely on lunatic methods. Rather, he trained extremely hard but very smart, stuck to a controlled but nutritionally balanced eating plan, and watched his body steadily chisel itself down to nothing but lean, taut muscle.

Before he knocked audiences on their asses with American History X, Edward Norton wasn't much more than a solid actor with a bad haircut and few decent flicks under his belt.

Then he stomped onto the screen as Derek Vinyard, a raging neo-Nazi skinhead with the kind of physically imposing look that would make most men cross the street. Norton didn't just have the cut biceps and chiseled chest of a typical Hollywood leading man, he looked like a guy who had spent some time lifting weights in the joint. So how did the scrawny Ivy Leaguer go from Yale grad to jail bird? A high protein diet mixed with strength-building exercises like squats and presses.

His coach Anthony Krotes put the emphasis on weight training with heavy weight and low repetitions. The result was 30lbs of muscle and a lean, mean look that perfectly suited his tough character in the movie.

Christian Bale didn’t just gain 42 pounds to play New York con man Irving Rosenfeld in David O. Russell’s ‘American Hustle,’ he also shaved part of his head to give extra life to Rosenfeld’s rather elaborate comb over. Bale even herniated a disc in his back as a result of his decision to give his character a slouched posture, which dropped Bale’s real-life height by three inches.

‘American Hustle’ isn’t the first time Bale has created a character with a physical tweak — he famously lost more than 60 pounds for his role in ‘The Machinist’ — but it might be his most striking transformation. Take what happened, for instance, when co-star Robert De Niro was introduced to Bale and the rest of the film’s cast before shooting a key ‘American Hustle’ scene.

“When Robert met the whole cast, he shook their hands the day we shot that scene,” Russell said at the press conference. “After he met everybody he said, ‘Who’s that guy?’ I said, ‘You just shook his hand, that’s Christian Bale.’ He said, ‘No, that guy.’ I said, ‘Yeah, that’s Christian Bale!’”

De Niro, who had never worked with Bale before “American Hustle,” was impressed.

“He stared and said, ‘Wow, he looks so different. It’s great,’” Russell recalled. “He didn’t realise he had just met Christian, so I had to reintroduce him again.”

Kit Harington suffered from body dysmorphia (excessive anxiety about the appearance of one's body) while working out for this role. He said he became completely obsessed with it to the point where he was "going to the gym three times a day for six days a week."

He suffered from a case of "exhaustion" and eventually his trainer stepped in to rein him in. But he said that he was "proud of what he achieved in the end".

Back in his Van Wilder days, Ryan Reynolds lived like a frat boy. “I was pretty unhealthy,” he admits. “I didn’t care what I ate or what I drank.” Then came Blade: Trinity, and the comic actor got serious. After three months, six-day-a week workouts, and a 3,200-calorie daily diet, Reynolds gained 25 pounds of muscle.

“That time changed my life because it taught me you can actually do things that were previously impossible,” he says.

Impossibilities like running the New York City marathon (at a time of 3 hours, 50 minutes). Or climbing the 8,000-foot Machu Pichu, one of the fitness feats left on his to-do list.

It’s hardly coincidental that Reynolds' career has taken a meteoric trajectory since bulking up for Blade. Not only has he acted alongside Oscar winners like Denzel Washington and Sandra Bullock, he’s also been offered countless superhero roles, like The Green Lantern and Deadpool in X-Men Origins: Wolverine.

Before there was Christian Bale, Robert De Niro was the king of transformational method acting — and no film establishes this better than the Martin Scorsese classic Raging Bull. In the film, DeNiro plays Italian-American middleweight boxer Jake LaMotta, whose self-destructive behavior is chronicled over the course of several decades, and De Niro takes it upon himself to show those decades of wear through his real, physical appearance.

At the time of the film’s release, De Niro’s 60 pound weight gain was the most by any actor for a film role, but what makes the actor’s physical change so remarkable is the extremes he went through during the course of one shoot. For the majority of the film, De Niro was required to maintain the body-type of a boxing contender and only in the last scenes in the film, which depict an older, overweight LaMotta, does De Niro swing wildly in the opposite direction.

And as if the weight gain alone wasn’t enough, De Niro added the weight in truly epic fashion: the production was shut down for several weeks while the actor went to Italy and ate as much pasta as he possibly could. By the time he got back, Scorsese was so alarmed by De Niro’s weight gain and labored breathing that production was again shut down as the director feared for the actor’s health.

The shooting of the movie and De Niro's dedication to the role earned him serious respect in the film industry, on top of his amazing acting skills, and set the bar for all actors doing transformative roles since.

Charlize Theron gained 30lbs for ‘Monster’, the movie role that showed audiences Theron was far more than a pretty face. Charlize Theron’s weight gain for Aileen Wuornos, the real life serial killer she portrayed, showed how committed she was to the role and her position as an actress in Hollywood.

Charlize Theron’s diet, and that word is used loosely, for her role in ‘Monster’ consisted of donuts and potato chips to pack on the 30lbs needed to look more like Wuornos. It wasn’t the first time she put herself through dieting of some kind for a role – though the actress did the opposite when she portrayed a dying woman in ‘Sweet November.’

However, Theron has said that getting “fat” wasn’t the actual goal in her makeover for Wuornos, who she says wasn’t fat at all. It was more about lifestyle, letting herself go so she could get closer to the place Wuornos was physically.

To prepare for the part, the usually tall, slender beauty looked unrecognizable — gaining 30 pounds, wearing prosthetic teeth, piling on make-up and practicing a tougher physical posture. "Monster" writer-director Patty Jenkins spoke to CNN about Theron's transformation, saying it was less about making Theron "fat and ugly" and more about the little things. "Yeah, just shocking because it was little details. It was, 'Oh, she was homeless. She lived on the street in bad weather. OK, well that means sun damage.' Well, then we addressed the sun damage. She was insecure about her hair, OK, well, then we address the hair. It was little little layers and then suddenly she's Aileen," Jenkins said.

Damon estimates that he gained between 25 and 30lbs in preparation for the movie 'The Informant,' directed by Steven Soderbergh.

"It wasn't necessarily that I needed to be fat," he said. "It was that I needed to be doughy."

Even though the weight-gain was required for the role, that didn't stop Damon's friends from mocking him mercilessly.

"Some things are just self-evident and don't even require making fun of," his best friend Ben Affleck said. "I mean the man buys two seats on an airplane!"

So how did he manage to gain so much weight? "I just stopped working out and basically just ate whatever I wanted," he said. "I ate a lot of In-N-Out, a lot of burgers, a lot of beer and basically had a great time ... When you're in your 20s you can do that kind of stuff. When you're in your 30s, its a whole different ballgame."

Jake Gyllenhaal dropped 30lbs for the movie, ‘Nightcrawler.’ “I made a lot of choices physically,” the actor, who ran 15 miles a day just going between his house and the set, said.

In the film, Gyllenhaal plays Lou Bloom, a wild-eyed paparazzo who stalks the moonlit streets of Los Angeles in search of sordid and shocking news. Although no one would call him beefy, the star wanted to look as gaunt as his on-screen alter ego, which meant subsisting on a diet of kale salad and chewing gum while filming the role.

According to the actor, this diet, along with all the running, took a toll on his body and his personal life.

“The running thing, you’re pretty hungry because you’re not eating a lot of food,” Gyllenhaal said. “You’re lonely because you’re not meeting your friends for dinner. People go, ‘Hey, you want to meet for dinner after work?’ I go, ‘Well, I’m shooting all night.’ ‘All right, you want to meet for lunch?’ I’m like, ‘I can’t!’ So I’m gonna go run.”

It was also a transformation that Gyllenhaal didn’t notice until well after the fact, when the movie was in post-production.

“I don’t think I was aware,” he said. “I don’t think I was aware until a few months ago and we were going through all the cuts, and you start to separate from the character and go, ‘Wow,’ you know?”

In his quest for authenticity in his role in the film ‘Gandhi,’ Mr. Kingsley not only shaved his head and lost 20 pounds on Gandhi's vegetarian diet, but he also studied yoga, began to meditate and learned to spin cotton thread on a wooden wheel, as Gandhi had done while holding conversations.

For Mr. Kingsley, such training is the catalyst for an alchemy even he does not understand. ''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,'' he explained.

The 28-year-old actor played real-life Israeli adventurer Yossi Ghinsberg, who was left stranded in an uncharted part of the Bolivian Amazon jungle for three weeks in 1981. He foraged for fruit and eggs from nests to survive, losing 35lbs as hunger, infection and disease took its toll.

But while Radcliffe has denied following the same diet for two months in preparation, his meagre diet didn't consist of much more than that.

"I ate just one chicken breast and a protein bar for two weeks before the shoot in order to look thin," he said.

"It's not recommended, it's a really unsafe way to use weight. It was horrible but it was worth it for the meal afterwards."

"I'm not a method actor, but it would seem weird if I was playing this guy stuck in the jungle and going home, having a lovely steak dinner at the end of the day."

The actor worked with fitness trainer Patrick Murphy four to five times a week for four to six months to prepare for ‘Baywatch,’ while following a strict, clean diet that entailed giving up sugars and carbs completely for days on end.

"Patrick's training was confusing at first...I just thought I was showing up to lift weights and get a deeper six pack (which is hard enough already)," Zac said. "But rather than the typical bodybuilding type of movements I had become accustomed to, 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."

But which workouts did the actor not enjoy so much? Group circuits with power moves. What exactly does this entail? Something like "20 alternating jump lunges in one place, 20 jump squats, 60 mountain climbers, power pushups, followed by a run up five flights of stairs, then one-leg squat hops using a TRX rope," explained the trainer.

Rest…for one minute. Then he would have to do the circuits again…twice. "That's more than 1,000 repetitions on the body," he added. To prevent fitness plateau, the trainer would switch up the routine to push the actor harder.

To recap, in order to get Zac Efron-status fit, we need to work out three times a day, change up our workouts, listen to our body, correct our form and eat a whole-foods-form diet. Easy.

J.K. Simmons seriously underwent a shred in order to play Commissioner Gordon in Justice League.

Aside from a tremendous amount of dedication to his regimen, Simmons credits part of his success to his trainer Aaron Williamson. An ex-Marine, Williamson's been providing elite-level training—morphing Hollywood A-listers into bona fide muscleheads like he's cranking out action figures on an assembly line—to the likes of Zac Efron, Dwayne Johnson, Jamie Foxx, and Jai Courtney. He first got his hands on Simmons in 2015 to help him shape up for Terminator Genisys.

At first, Simmons wanted to escape the doldrums of the film's set, which was based in Louisiana, but after shooting wrapped Simmons felt he was ready for a full-body change.

"He wanted to get into the best shape he had ever been in," Williamson says, adding, "J.K.'s goal was to adopt a healthy lifestyle and never have to worry again about health issues."

Colin Farrell says it wasn’t hard to gain 40 lbs. in just two months for his new role as a father of two in the satirical comedy The Lobster– it just meant he had zero portion control.

“I just ate and didn’t move for a while,” Farrell, 39, tells PEOPLE of how he packed on the pounds. “It was stuff I normally eat, but just a lot more of it. People talk about portion control – there was no control!”

As soon as the film wrapped, Farrell dedicated himself to losing the extra weight. "I dropped the weight so quickly just by starving and working out," he explained.

“When it came to conditioning my body for the role of Charles Bronson there was no official regime: I did very non-specific exercises such as press ups, pushups, abs work and resistance training with the help of my boy Pnut, who is 16 stone of pure muscle and also an ex-US Marine. Essentially I was using him as my machine; he was like a walking gym. My approach was to do a lot of repetitions in order to send messages to my muscles: this helps them start to grow in a way that you can’t make them in the gym. To achieve dense muscle, you need a specific kind of training. Also, to “become” Charlie Bronson I had to quickly put a lot of weight quickly on my forearms, chest and neck. By the time I’d finished, my legs looked like those of a stork in comparison to the top half of my body.”

“I had five weeks to make the transition into Britain’s most dangerous criminal and it was a race against the clock: We didn’t have any time to waste, so I started eating and my arse very quickly got very fat. For Bronson, I put on about 7lbs 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. I needed to put a layer of fat on my body, because Bronson when he was younger was a big guy, a brawler. My diet was lenient as we weren’t going for the Bruce Lee look and we weren’t looking for the cut.”

“Initially Charles Bronson was very disappointed when he saw me. He said “This kid will never be able to play me.” I just told him, “Don’t worry Charlie I’ll fix it.” When I came back two weeks later he was thoroughly impressed with what he saw. His sister had been telling him good things about the way I'd been doing his voice and the way I moved like him, but his concern was the physicality of my portrayal of him, but I think I did a good job in the end.”

Ryan Gosling revealed that he was fired from Peter Jackson's 2009 awards contender "The Lovely Bones" because his 60-pound weight gain did not sit well with the director and his fellow producers. Gosling said his much-ballyhooed weight gain -- fuelled by drinking melted Haagen Dazs ice cream when he was thirsty -- was all a part of how he saw the character of Jack Salmon, the grieving-father role ultimately filled by Mark Wahlberg. "We had a different idea of how the character should look," Gosling said. "I really believed he should be 210 pounds." Jackson disagreed, and dropped Gosling days before production began in 2007. "We didn't talk very much during the pre-production process, which was the problem," Gosling said. "It was a huge movie, and there's so many things to deal with, and he couldn't deal with the actors individually. I just showed up on set, and I had gotten it wrong."

"Then I was fat and unemployed."

The 30-year-old actress was so committed to the role that she chopped off her signature long brunette tresses and dropped 25 pounds for the film ‘Les Miserables.’ There were even rumors she was on an extreme crash diet and eating fewer than 500 calories a day in order to achieve rapid weight loss. But according to Hathaway’s representative the reports were “a huge exaggeration,” adding that Hathaway was indeed on a special diet, but she was consuming more than 500 calories a day.

However, rumors of a starvation diet don’t sound too far off from reality. The actress lost 10 pounds courtesy of a strict cleanse before filming began, and followed it up by losing another 15 pounds by eating just two thin squares of dried oatmeal paste a day. For Hathaway, losing the weight for the role was a consuming experience:

“I had to be obsessive about it—the idea was to look near death. Looking back on the whole experience—and I don’t judge it in any way—it was definitely a little nuts. It was definitely a break with reality, but I think that’s who Fantine is anyway,” she explained.

“I was in such a state of deprivation—physical and emotional. When I got home, I couldn’t react to the chaos of the world without being overwhelmed. It took me weeks till I felt like myself again.”

“You need to put on weight,” McGregor recalls the creator of ‘Fargo’ Noah Hawley saying to him at a restaurant in Los Angeles last October, three months before production began. At the time, McGregor was 45, and at his fittest. He had just finished filming Trainspotting 2 in Edinburgh, Scotland, where he and cast member Jonny Lee Miller regularly exercised, running around and up an imposing mountain called Arthur’s Seat.

But McGregor didn’t protest. “I ordered a massive dessert and started putting on weight from that second onward,”

“From October until January, when we started filming, I just started eating whatever I wanted. I made sure that I had carbs with everything and French fries with everything. I didn’t have any technique other than eating a lot. I think if you spoke to a dietician, I probably did it all wrong.”

He never weighed himself, but he did have to buy new Levi’s that were three inches larger in the waist. “It’s quite nice when you’re ordering — you can order whatever you like,” he says. “But the truth is I would go to bed every night not feeling very great. I’m a small guy. I’m not really used to carrying weight. It doesn’t make you feel great. I like to feel fit and healthy. But it was effective. It worked.”

Michael Fassbender lost 42 Pounds for the 2008 movie ‘Hunger.’ Fassbender played Bobby Sands, a young prisoner who led the second Provisional Irish Republican Army hunger strike in 1981 and died after 66 days without food. Off-screen, Fassbender went on a fast of his own: The combination of a 900-calorie-a-day diet plus exercise (skipping, yoga, walking) resulted in about a 42 pound weight loss. “It is such a psychological prison,” he’s said of the process. His final weight: A reported 127 pounds.

Theoretically, Fassbender was losing weight in a recommended way – by reducing his caloric intake and exercising. But he took it to an extreme.

George Clooney gained 35lbs on a pasta-heavy diet to play CIA operative Robert Barnes in the movie ‘Syriana.’ The actor also shaved his hairline for the right look for his aging character.

During filming, Clooney suffered a spinal injury performing a stunt. Due to the weight he gained for his role, the injury left him bedridden for a month and caused severe migraines, which prevented him from doing publicity for Ocean's Twelve (2004). The injury was eventually corrected with surgery. Clooney has since called his weight gain "pretty stupid".

"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."

To portray a female boxer, Hilary Swank had to not only learn how to box, but mold her body into the guise of someone who has probably spent her whole life training. Swank had about 90 days to do it.

"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 said. "The producers asked me to gain 10 pounds of muscle. I gained 19 pounds of muscle. I started at 110 and went to 129. And in order to do that, I had to eat 210 grams of protein a day. Now, your body can only assimilate so much protein, so I had to eat every hour and a half. So with a meal, 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. I had to drink flax oil. Flax is a really important oil for your brain and to also just keep everything moving when you're eating that much protein. It's a really important fat. Like one tablespoon of Flax oil has like 15 grams of fat in it."

Even her sleep was coordinated into her daily regimen. "The thing was, I needed nine hours of sleep a night because your muscles have to be able to rest in order to build or you actually reverse yourself. So I slept nine hours a night but I had to wake up in the night and drink protein shakes because I couldn't go that long without eating."

Before being cast in Stanley Kubrick`s ‘Full Metal Jacket,’ Vincent D`Onofrio was a trim, good-looking athlete, a rugged 6-feet-3 and--with his full head of curly dark hair--the kind of man who makes women`s heads turn.

But after winning the part of Leonard, the fat, inept and increasingly disturbed Marine recruit who serves as the dramatic fulcrum for the first half of the film, D`Onofrio was obliged to put on nearly 70 pounds and shave his head--a physical transformation that had a shocking effect.

“It changed my life,” he said. “Women didn`t look at me; most of the time I was looking at their backs as they were running away. People used to say things to me twice, because they thought I was stupid.”

The hard part was having to gain all that weight, which proved as difficult as losing it later.

“I gained weight everywhere,” D`Onofrio said. “My thighs were tremendous, my arms were tremendous, even my nose was fat. I had a tough time tying my shoelaces, but this was the only way I could play Leonard, because I had to be weak-minded in the same way. Because of the weight and the fact that he was totally out of his element, Leonard`s mind became weak.”

Inhabiting Leonard`s body had a profound effect on D`Onofrio`s perceptions. “It makes you realize all those typical things about beauty being deeper than what you would think,” he said.

Will Smith was a relatively slim guy prior to Ali. He weighed about 185 pounds which is light for someone that stands at 6 foot 2 tall. To look the part to play Ali, Will Smith had to pack on 35 pounds of muscle to look like a real heavy weight boxer.

Critics were skeptical at the news of the skinny Will Smith playing the mighty Ali, but he hit the gym and after working out 5 days a week for 6 hours a day for almost a year he was in the shape of his life.

“If I’d had Will when he was 20, I could’ve made a champion out of him. He’s got the physical skills and, more importantly, he’s got the heart,” said fitness coach Angelo Dundee.

In addition to all the functional training Will had to do a lot of endurance training, and some of it included running through snow wearing boots as well as a lot of weight lifting. Will Smiths bench press increased from 175 pounds at the start of the year to 365 pounds by the time shooting for the film started.

“Beyond looking like a fighter, my goal was to learn to think like a fighter,” says Smith. “To do that I had to eat like a fighter, sleep like a fighter, assess situations in life like a fighter… become a fighter.”

Taylor Lautner isn't a naturally strong guy, but his career depends on becoming brawny. Between the first and second Twilight films, his character grew into a powerful werewolf. That meant he needed to gain 30 pounds of muscle in a year. Which he did.

Think about that: Taylor Lautner used to be a 5'10", 140-pound, bony teenager, and now he's a rippled fitness animal. If he can overcome physical shortcomings, anyone can.

How did Emma Stone transform into tennis legend Billie Jean King? It took a lot of sled pushes, protein shakes and a man named Jason Walsh.

"Emma took it very seriously," Jason said. "This is somebody's story that she's taken on. She wanted to make sure she could do everything possible to portray Billie Jean King in the right way."

The first step: nutrition. Jason said they needed to dial in Emma's diet by increasing calorie and fat intake, which helped for her to put on weight. Emma isn't built like a tennis player or a pro athlete, so in order to look like one, putting on those pounds and muscle was essential for the aesthetic element of becoming Billie Jean. According to the celeb trainer, the easiest way to accumulate those calories is to drink them.

"The last thing you want to do is force someone to eat a lot more food. Your hunger is going to go up naturally because your metabolism is going to go up from the training," Jason explained, adding that Emma became almost insatiable because of the intense workouts he was putting her through. "Protein shakes were an easy way for us to get a lot of nutrients and a few hundred calories in a single drink that tasted really good. She actually looked forward to it."

As for training, Emma would meet Jason five days a week, twice daily for four of those five days. Eventually, Jason transitioned the actress into fewer sessions as filming approached. In the mornings, they would work on what James calls "complex movements": sled pushes, squats and lunges—the heavy stuff. The afternoons were for "secondary movements," or what Jason describes as "less taxing, but good for aesthetics." Think exercises that target the abs and arms.

According to Jason, Emma was doing 300-pound hip thrusts, a few hundred pounds on sled pushes and her dead lift was up to around 185 pounds (wow!). But Jason is most impressed with is the star's resilience.

"What I'm really proud of for Emma and for actresses like her that we end up training is that we keep them from getting injured," he said. "When an actor has to play tennis all day long and do all these things for a movie, the chances of them getting injured if their body isn't strong and resilient is pretty high. Then that's going to stop production, and you've got other issues there."

He also said that with Emma's training came with powerful psychological benefits. "It gave her a level of confidence and it helped her believe that she was Billie Jean King. It really does give women confidence to be strong like that."