15 Stars Who Transformed Their Bodies For Movie Roles

1. John Krasinski

Film: "13 Hours: The Secret Soldiers of Benghazi"

He played affable Jim Halpert on "The Office" and some people know him as Mr. Emily Blunt but when it came time to play a Navy SEAL, John Krasinski wanted to get ripped. In just 16 weeks, Krasinski transformed himself, saying, "I think there's a part of you where you become addicted to it. I love feeling strong."

2. Christian Bale

Film: "The Dark Knight"

When prepping to play Batman, Christian Bale had just come off a 60-pound weight loss to play an insomniac factory worker in "The Machinist" before bulking up and getting strong for "The Dark Knight."

To get in shape, Bale used a private trainer and gutted through intense gym workouts five days a week. But, don't mistake Bale's body transformations for a love of working out. He tells Men's Fitness, "I'd done 'American Psycho,' and I bulked up purely for that part. But people start just going, 'Oh yeah, that guy's a real workout fanatic,' and that's not me, that's Patrick Bateman. It was a nice way to kill that dead by just destroying your body completely."

3. Chris Hemsworth

Film: "In The Heart Of The Sea"

To transform himself for Ron Howard's epic "In the Heart of the Sea," Chris Hemsworth dropped 33 pounds by living on 500 calories per day! And while his Thor-like body shrunk, his moods were tough to live with. Hemsworth admits wife Elsa Pataky had to be very patient with her cranky husband through filming.

Hemsworth tells People, "She had to put up with my moods unfortunately." He adds, "By the end of it, she was happy for me to start eating again."

Turns out men can get hangry, too.

4. Matthew McConaughey

Film: "Dallas Buyers Club"

When prepping for his role as a man diagnosed with HIV/AIDS in "Dallas Buyers Club," the "Magic Mike" star dropped a hefty 38 pounds. And while his rail-thin appearance was perfect for the role, the tall Texan admits his energy level suffered.

"Overall, [I've] probably got 35 percent less energy, but there's been plateaus," McConaughey tells HitFix. "Getting past 170 was really hard, but then once you get [to] 167, the next seven come off easy. Getting past 160, really hard. But then you fly down to 150. Getting past 150 was really hard and then, bam! Got down to 143 and that's where I want to be. So, once you get past the plateau, your body seems to understand, 'OK, this is where we're leaving now, this is where we are,' and so the energy rises."

The Academy Award must have felt that much sweeter.

5. Mila Kunis

Role: "Black Swan"

To star in the intense film "Black Swan," Mila Kunis famously lost 20 pounds. On her already tiny frame, that's a lot. Ashton Kutcher's wife admits that her body has never been the same since.

"My shape is different," she tells Harper's Bazaar. "When I got down to 95 pounds, I was muscles, like a little brick house, but skin and bones. When I gained it back, it went to completely different areas."

"I'd be happy if my a-- got bigger," she adds. "All the weight that left my chest went to my side hip, my stomach."

We know the feeling.

6. Anne Hathaway

Film: "The Dark Knight"

Anne Hathaway is already a notoriously healthy eater and a vegetarian, but she kicked it up a notch to squeeze into that latex Catwoman suit for "The Dark Knight." And though she told Chelsea Handler she lived on just "kale and dust," Hathaway actually ate three small meals a day, two snacks and engaged in a lot of exercise.

It almost sounds doable!

7. Robert Downey Jr.

Film: "Iron Man"

At 50 years old, Robert Downey Jr. isn't your usual spry young action star, but that didn't bother the devout yogi when prepping for his role as Iron Man.

"I'm not particularly tall, strong, fast or aggressive," Downey told Men's Fitness. "But I'm not faking it."

In addition to yoga, Downey cut back on cardio and increased his weight training while consuming 5,000 calories a day to pack on 25 pounds of muscle.

That worked out pretty well for him.

8. Adrien Brody

Film: "The Pianist"

Adrien Brody may have won an Oscar for his portrayal of a Warsaw ghetto survivor, but shedding 30 pounds from his lean, tall frame took its toll.

Brody tells the BBC, "There is an emptiness that comes with really starving that I hadn't experienced."

Hopefully, that Academy Award helped.

9. Jake Gyllenhaal

Film: "Night Crawler"

Jake Gyllenhaal is famous for digging deeply into his roles, so when it came time to portray Lou, a man who stumbles into the underground world of Los Angeles' freelance crime journalism, Jake knew he had to transform his look.

"I knew that [Lou] was literally and figuratively hungry," he tells US Weekly. The actor's dramatic weight loss kept him connected to the character.

10. Chris Pratt

Film: "Zero Dark Thirty"

Playing a badass soldier in "Zero Dark Thirty" requires a different physique than his role on "Parks and Recreation" did, and Chris Pratt talked to Conan O'Brien about moving up and down in weight.

"I've always been a little softI like to eat and I don't like crunches," Pratt told O'Brien. "I had about five or six months, and I really busted my ass to get in good shape."

But his hot bod didn't last long, he admitted. "Almost immediately after I wrapped that movie, I gained 60 pounds to play a role in another movie. I'm kind of like a fatass [now]. I have a little extra belly going on."

And then came "Guardians of the Galaxy" and "Jurassic World".

11. Jared Leto

Film: "Dallas Buyers Club"

Jared Leto is known for jumping into a role, but his transformation into a young man suffering from AIDS was undeniable for "Dallas Buyers Club." Leto told Entertainment Tonight, "I waxed my entire body, including my eyebrows. I've lost a lot of weight because I'm playing a young person with AIDS. It's been challenging but really inspiring too."

Photographer Terry Richardson documented Leto's weight loss.

12. Matt Damon

Film: "The Informant"

Matt Damon has transformed himself for many roles, from Jason Bourne to Liberace's teen lover in "Beyond the Candelabra." But for 2009 film "The Informant!" Damon bulked up instead of down. Turns out that transformation was pretty easy.

"At my age, all I had to do to gain weight was eat the way I did when I was in college and the weight went on instantly," Damon revealed. "It was a little horrifying."

13. 50 Cent

Film: "All Things Fall Apart"

Fiddy's known for his ripped arms, but to prepare for his role as a football player suffering from a deadly disease, the rapper whose real name is Curtis Jackson had to get lean. By following a liquid diet for nine weeks combined with working out three hours a day, Jackson went from 214 pounds to 160 pounds.

Jackson explained his commitment to the film, saying, "I had a friend of mine who actually experienced cancer, and it's what motivated me to write this screenplay. You don't have to make everything personal, but that project was. That's why I committed to playing a role where I lost 54 pounds. I had to discipline myself enough until I achieved it but I got it."

14. Renée Zellweger

Film: "Bridget Jones's Diary"

The tiny star packed on an estimated 30 pounds for her role as the perpetually single Bridget Jones. And now that she's filming the third Bridget Jones movie, "Bridget Jones's Baby," she's packing on the pounds onto her rail-thin frame by drinking high-calorie drinks.

For the past two films, Zellweger had a good time putting on the weight. She told Hollywood.com, "It was nice to say, 'I'd better have a garlic bread with this pizza. It's for the good of the film It's my responsibility to have that piece of pie."

No wonder she signed on to do a third film.

15. Russell Crowe

Film: "Body of Lies"

Russell Crowe is famous for doing what it takes to become his characters. So when it came time to shoot the Ridley Scott thriller co-starring Leonardo DiCaprio, in which Crowe plays a veteran CIA agent, Crowe bulked up.

"If you want to put on weight, you just elect to live a sedentary life style," Crowe tells Access Hollywood. "Just as soon as you stop actually being active and decide to eat whatever you want, then these two things will combine very quickly."

Sadly, we know what he's talking about!