You might have the idea that acting is an easy job, and maybe sometimes it totally is (see Meryl Streep in Mamma Mia!). For the actors in the following roles, though, that certainly wasn’t the case. These actors made total transformations and proved some serious commitment to their craft.

#20. Jake Gyllenhaal in Southpaw

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He had to gain 45 pounds after Nightcrawler, most of it muscle.

“I went into full training-camp mode and I got myself—what I consider in my mind as an actor—in shape to fight. I was literally learning the skills of boxing, which is not only for the body, but also for the mind. You can’t play a boxer and just look like a boxer; you have to believe you can exist in that world.”

#19. 50 Cent in Things Fall Apart

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Telling his best friend’s story was worth the 54 pound loss.

“I had so much muscle on me that it was hard for me to lose definition even as I got lighter and slimmer. I started running to suppress my appetite. Towards the end it was really difficult. It was like, if I don’t get close enough to what my best friend looked like to me at that point before he passed, then I’m not doing the story any justice.”

#18. Matthew McConaughey in Dallas Buyers Club

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He lost 47 pounds for his Oscar-nominated role.

“That was rough. I got down to 143 pounds and I was always hungry, and irritable. My body resembled a baby bird with its mouth open, crying, ‘Feed me, feed me,’ and you realize momma bird ain’t going to feed you. It’s hard.”

#17. Tom Hanks in Cast Away

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“The hardest thing was the time. I wish I could have just taken a pill and lost all the weight but the reality was that I had to start in October knowing that we were going to go back in February. 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, that was formidable. You have to power yourself through it almost by some sort of meditation trickery. It’s not glamorous.”

Welcome to being a woman, Mr. Hanks. Congrats on the ability to drop 50 pounds.

#16. Robert De Niro in Raging Bull

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You might have forgotten in recent years that De Niro used to be a serious actor – like in Raging Bull, when he packed on 60 pounds.

“The first 15 pounds was fun, the rest was hard work.”

#15. Anne Hathaway in Les Misérables

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For her role as Fantine, Hathaway hired a nutritionist to help her lose 25 pounds-10 before filming started and another 15 (by basically starving herself) during the 13-day shoot.

#14. Matthew Fox in Alex Cross

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His thoughts on losing 44 pounds:

“If I’m honest, sometimes I f**king hated it. I guess if you removed the ‘result’ part of it then I can’t say I enjoyed it.”

#13. Matt Damon in The Informant

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I know these have their downsides, but it has to be more fun to gain than lose, right? Thanks for being honest, Matt Damon.

“It was very, very easy to gain the weight. It was very, very fun, probably the funnest time I had working, because I didn’t have to go to the gym after work and I just ate everything I could see.”

#12. Chris Pratt in Guardians of the Galaxy

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He lost 65 pounds, but based on this before picture, some of that needed to go…

“Six months seems like a long time unless you’re looking backwards…all you have to do is just a few things everyday and remain consistent, and time will fly just as fast as it flies if you’re working hard or not. If you just cut the crap out of your diet, and if you spend an hour a day doing something physical that will make you sweat, six months will pass by, you will feel better mentally, physically, spiritually — it all is tied together.”

#11. Renée Zellweger in Bridget Jones’s Diary

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In the opposite track from most of these actors, Zellweger had to pack on the pounds – she gained 20 pounds to play the iconic British role. Twice. According to her, it’s not quite as much fun as you’d think, either.

“For two days it’s bliss and then you’re full, OK? And you can then indulge all your fantasies about over-eating.

“Fantasies about non-stop chocolate consumption or your fantasies about ordering the pizza and the spaghetti and the garlic bread.

“Then after a week your glucose levels are going crazy. You’re up and down and all over the place. It doesn’t feel good, and no one wants to hear that, but it’s the truth.”

#10. Jared Leto in Chapter 27

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He gained 67 pounds and put his health at risk for this part.

“Really, it’s a stupid thing to do. I got gout, and my cholesterol went up so fast in such a short time that my doctors wanted to put me on Lipitor, which is for much, much older people. Again, though, a fascinating journey.”

#9. Russell Crowe in Body of Lies

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He gained over 60 pounds, and learned how hard it is to lose it.

“If you want to put on weight, you just elect to live a sedentary life style. Just as soon as you stop actually being active and decide to eat what ever you want, then these two things will combine very quickly.”

#8. Mila Kunis in Black Swan

Everyone knows ballet dancers are thin, but even Mila Kunis had to drop 20 pounds for the role.

“I trained four hours a day, seven days a week, for seven months. I had one day off on my birthday and half a day off for the Emmys and the Golden Globes. On those days my ballet instructor worked with me from 5 am to 11 am, then I went to hair and make-up and on to the awards shows.”

#7. Chris Hemsworth in In the Heart of the Sea

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He’d already lost quite a bit for Blackhat, and dropped an additional 15 pounds for this role.

“That’s all we spoke about. You’ve got 15 burly blokes on the sea and all we talked about was our diet and who’d lost more weight and who’s looking really skinny. It’s ridiculous!”

#6. Jake Gyllenhaal in Nightcrawler

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He lost 30 pounds for the role, and quickly realized that there are more side effects than a trimmer waistline:

“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.”

#5. Christian Bale in The Machinist

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After losing 63 pounds, Bale nearly disappeared. Which isn’t something he would ever like to do again:

“I have no goal of seeing if I can become invisible one day, eat so little that I disappear. I didn’t take this job because I went, ‘Oh, there’s a physical transformation needed.’ I always go, ‘Damn! There’s a physical transformation needed!'”

#4. Colin Farrell in Triage

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He approached the 44 pound loss in a very practical manner.

“I lost weight because my role demanded it. It was all very healthy.”

#3. Jared Leto in Dallas Buyers Club

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Leto lost 40 pounds to play a man dying of AIDS, and even though the part earned him an Oscar, it couldn’t have been easy.

“It changes the way you walk, the way you sit, the way you think.”

#2. Charlize Theron in Monster

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She gained 30 pounds and a set of prosthetic teeth, but lost her eyebrows.

“I first began stuffing myself with Krispy Kreme doughnuts, but after a while I got sick of them. 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.”

#1. Natalie Portman in Black Swan

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The already thin actress also dropped 20 pounds for her role in the dark film.

“There were some nights that I thought I literally was going to die.

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.”

h/t: Movie Pilot