When it comes to losing weight healthfully and sustainably, experts warn against following extreme diets. But resorting to calorie restriction at the risk of malnourishment is no foreign tactic among celebrities seeking to prime their bodies for movie roles. Stars from Anne Hathaway to 50 Cent to, most recently, Chris Hemsworth and more have all slashed their daily caloric intake to shed pounds fast.

Here’s how those three celebrities, plus seven others, either dropped or gained pounds fast—and for which roles:

1. Chris Hemsworth


Actor Liam Hemsworth’s older brother may be known for his buff body, but these days the man who plays Thor has been sporting a leaner physique to embody a shipwrecked man at sea in the upcoming flick “In the Heart of the Sea.” The movie stars Chris Hemsworth as Owen Chase and marks the film adaptation of the Herman Melville classic “Moby Dick.” The actor told Entertainment Tonight (ET) in July that for three or four weeks, he is preparing to drop down to 500, 600 or 700 calories a day.

“It’s going to be pretty uncomfortable, but we’ll be together in our misery,” he told ET. “I spend more time thinking about food than anything else at the moment.”

2. Christian Bale


“The Dark Knight” actor has shrunk his frame for not one, but two roles on the silver screen: first for “The Machinist” and second for “The Fighter.” Bale famously lost 63 pounds— or a third of his body weight— with vitamins, a sparse diet and lots of exercise to play a chronic insomniac in the former movie, in which he plays an industrial worker who doesn’t sleep for an entire year. For “The Fighter,” the 6-foot-tall actor downsized again to play Dicky Eklund, a former professional wrestler who becomes addicted to crack cocaine.

"I will adjust to what is needed,” Bale told People magazine in 2005, “but only if I have quite an obsession for the role.”

3. Lily James


Nutritionists have time and time again debunked the supposed health benefits of going on a liquid diet to trim your waistline— as it can throw your metabolism out of whack and interfere with your digestive system— but that hasn’t stopped celebrities like Gwyneth Paltrow and Beyonce from plugging the popular weight loss method. According to E! Online, “Cinderella” actress Lily James also reportedly opted to go on a “cleanse” to squeeze into her corset for the title role. But the actress has said her choice wasn’t exactly an effort to lose weight— rather, it was to 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," the 25-year-old British actress 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.”

4. Charlize Theron


The outspoken animal activist and native South African gorged on donuts to gain 30 pounds for her role as a prostitute and serial killer in 2003’s “Monster,” for which she won an Oscar. Theron, who usually is a size 8, told SplicedWire.com that her weight gain goal “wasn’t about getting fat.”

“Aileen (my character) wasn't fat,” she told the since-defunct movie review site after making the film. “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. It was about getting to a place where I felt closer to how Aileen was living."

5. 50 Cent


The recently bankrupt rapper released photos of himself looking emaciated in May 2010 for his role as a football player who has cancer in the flick “Things Fall Apart.” Born Curtis James Jackson III, 50 reportedly went from weighing 214 pounds to only 160 in only nine weeks by sticking to a strict liquid diet. The rapper told the Associated Press in 2010 that when he was shot in the jaw in 2000, he could also drink only liquids, which had caused his weight to drop to 157.

"This time it was a lot tougher for me," the 6-foot-tall rapper told the Associated Press. "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.”

6. Anne Hathaway


“The Devil Wears Prada” star shed a reported 25 pounds and shaved her head to play Fantine, a prostitute dying of tuberculosis, in the 2012 film “Les Misérables.” The actress’ rep told The Huffington Post that she consumed fewer than 500 calories a day to achieve the feat. According to Vogue, Hathaway lost the first 10 pounds by following a cleanse before shooting began, and another 15 by eating two thin squares of dried oatmeal paste a day.

“I had to be obsessive about it— the idea was to look near death,” Hathaway told Vogue in 2012. “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.”

7. Matthew McConaughey


The BBC reported that Texas native Matthew McConaughey dropped nearly 50 pounds to play AIDS patient Woodruff in the 2014 Oscar-nominated film “Dallas Buyers Club.” McConaughey won an Oscar himself for the lead role, for which he reportedly lost 3 and a half pounds a week by using guidance from a nutritionist.

"I did it in as healthy a way as I found possible," he told the BBC.

8. Jared Leto


Jared Leto is also well known for his physical transformation as transgender AIDS patient Rayon in “Dallas Buyers Club,” but the 30 Seconds to Mars front-man also drastically changed his appearance for his role as John Lennon’s killer in the movie “Chapter 27.”

Leto reportedly gained 60 pounds for the role, which caused him gout-like foot pain and left him feeling poorly for a year after playing the character. He told the New York Daily News that he binge-ate and force-fed himself to achieve the weight gain goal.

9. Natalie Portman


The Harvard grad and avid vegan reportedly lost 20 pounds for her role in the Oscar-winning flick. Her co-star Mila Kunis also reportedly lost 20 pounds—dropping to a mere 95 pounds total for her role in “Black Swan.”

"In real life, it looked disgusting," Kunis told E! Online. "But in photographs and on film, it looked amazing."

Kunis said it took her five months to drop the weight but only five days to put it back on.

10. Renee Zellweger


The usually size-4 star gained 20 pounds to jump to a size 14 for her role as Bridget Jones in 2001’s “Bridget Jones’ Diary.” Zellweger dropped the weight she had gained yet continued to lose weight even after that. The public scrutiny over her frame reportedly left the star feeling violated. "I realized the influence of living in a society that focuses so much on physicality has affected me," she told Vogue in 2013.

“When the film was coming out, the question I was asked the most was regarding my weight ... I was followed around Heathrow [Airport] by a guy who wanted to take a picture of my backside. I don't understand the obsession."