For his role in the 2005 thriller The Machinist, Bale became “obsessed” with losing weight, so much so that he subsisted on a 200-calorie diet consisting of an apple, a tin of tuna, and black coffee.

His second method for changing his physique—drinking whiskey and smoking cigarettes—proved unsuccessful and was abandoned after worrying his family.  “I was waking up with heart palpitations and just not feeling right at all,” the actor shared.

He ended up dropping 62 pounds (28 kgs) in four months to play the insomniac machinist. At one point, his wife grew extremely concerned about his dramatic transformation.

“I caught her a few times removing her hand from in front of my mouth as I was waking up; she was just testing for breath. But even though it was discomforting for her, she liked the character I played.”

The Australian actor’s outstanding performance as Jean Valjean in the musical film Les Miserables earned him an Academy Award nomination for Best Actor and a Golden Globe for the same category.

To prepare for the leading role, Jackman lost 30 pounds (13 kg) and didn’t even drink water during his long hours on set. That sacrifice was essential for the opening scene when Jean is released from prison on parole after serving 19 years of intense labor.

Weirdly, he admitted, preparing for the role was tougher than getting ripped to play Wolverine.
 
“This was almost more physical in a way than an X-Men movie!” Jackman told Vulture. “I was spending even longer in the gym—like three hours in the gym—because I needed to be as emaciated as possible.”
 
However, looking back on that opening scene, the talented actor has no regrets. “I realized the sacrifices had been worth it, that the headaches, dizziness—and the grumpiness—had been a relatively small price to pay,” Hugh explained.

Miley was only 13 years old when she was cast as popstar Hannah Montana in the popular Disney Channel show. The experience involved working 12-hour days, getting “coffee jammed down my throat” and being put in “glittery tight” clothing, all of which weren’t ideal for a pre-teen.

“I'm this fragile little girl playing a 16-year-old in a wig and a ton of makeup. It was like Toddlers & Tiaras. I had f***ing flippers,” the Flowers singer told Marie Claire in 2015.

Wearing makeup, a wig, and extravagant outfits for four years had lasting effects on her mental health. “I was told for so long what a girl is supposed to be from being on that show,” she said.

“I was made to look like someone that I wasn't, which probably caused some body dysmorphia because I had been made pretty every day for so long, and then when I wasn't on that show, it was like, Who the f*** am I?"

This time, the chameleonic star had to gain 43 pounds (19 kg) to play the 1970s con artist Irving Rosenfeld in American Hustle. Before that, he had hit the gym and gotten ripped for Batman Begins.

The preparation to play Rosenfeld was probably less of a sacrifice than consuming a single apple a day.  “I ate lots of doughnuts, a whole lot of cheeseburgers and whatever I could get my hands on. I literally ate anything that came my way,” the actor explained to People Magazine.

Still, he had to slouch a lot during the scenes, a posture that ultimately caused him to herniate a disc in his back. He also admitted that losing all those pounds once the filming was over proved far more challenging than he had anticipated.

“I said, two months, flat, that'll do it. And I'm still working that off!” he said in 2013. “Now I know that when I was in my early 20s it would have been two months and that's it.”

Director Ryan Murphy said that Bomer’s 35-pound (15 kg) loss to play a journalist dying of AIDS in The Normal Heart was so severe that the actor struggled to move between takes.

Matt was so thin that Murphy once burst into tears when he saw him given his emaciated figure.

The director said: “I was so worried for his health, because he had taken it to such a level. He was in a chair getting a haircut, and he could barely turn to greet me, he was so weak.”

The first food that he ate after he was done filming the less-clothed scenes was a cracker, which he threw up. “His body had been so deprived for so long that he couldn’t hold any food,” Murphy explained.

Bomer received critical praise for his role in the drama romance film and won his first Golden Globe award for Best Supporting Actor.

Parrette had to dye her hair black for twenty years to play Abby Sciuto on NCIS and ended up becoming allergic to the hair dye. On one occasion, the natural blonde had a severe allergic reaction and was rushed to the hospital.

The actress had a rash and experienced severe swelling. “The other half of my face had become twice the size of my head," she shared.

Pauley posted the photo on social media to warn her thousands of followers about the dangers of hair dye allergies. “The most important thing to me is that anyone out there that dyes their hair, particularly black, you need to be aware of the symptoms.” such as itchiness, redness, or eczema.

After that traumatic episode, she said she would begin wearing a wig or using natural dye.

To play the manipulative crime journalist Lou Bloom in the neo-noir thriller film Nightcrawler, Gyllenhaal tried to eat as few calories as he could.

Ultimately, he dropped 30 pounds (13 kg) from his 180-pound frame in a process that became a “struggle.”

The actor, who also produced the movie, came up with the idea to make Lou look gaunt in a brainstorming session with director Dan Gilroy.

“I knew if I was hungry that I was in the right spot,” Jake told Variety. “Physically, it showed itself, but chemically and mentally, I think it was even a more fascinating journey. It became a struggle for me.”

Zac Efron revealed that he wasn’t a fan of the muscular body he worked so hard for on 2017’s Baywatch.

To transform himself into Matt Brody, Efron took diuretics for a long period, which caused him insomnia and depression.

In an interview with Men’s Health, the 36-year-old actor spoke candidly about his body transformation, labeling his ripped lifeguard physique “unattainable.”

"There's just too little water in the skin," he said. "Like, it's fake; it looks CGI'd. And that required Lasix, powerful diuretics, to achieve. So I don't need to do that. I much prefer to have an extra, you know, 2 to 3 percent body fat."

He shared that the movie came at a high price, and he struggled to get back to his usual self.

"I started to develop insomnia and I fell into a pretty bad depression for a long time. Something about that experience burned me out. I had a really hard time recentering.”

For some reason, Mark Hamill used permanent dye to color his hair purple for his two-episode guest appearance as Trickster on DC’s show The Flash.

“Road to Recovery From the Perils of Purple Hair. Took me 3 dye jobs to get back to normal.” the actor shared on X, along with a picture of himself wearing dozens of hair foils on his locks to get them back to their natural color.

He accompanied the funny snapshot with the hashtags #ACautionaryTale #HairDont #DudeWheresYourDignity.

The Ukrainian actress had to weigh 95 pounds (43 kg) to take on the role of Lily, a troubled ballerina, in 2010’s Black Swan.

Kunis, who is 5’4'', explained that she didn’t “starve” herself but consumed only 1,200 calories a day. (The recommended daily intake of calories for women is 2,000, according to the NHS).

To achieve this, she turned to the “awful” method of smoking cigarettes, which she had recently quit.

“I never watched what I ate [before]. It was one of those things, for the first time in my life, I got a food delivery service,” Mila told Entertainment Tonight in 2014 before adding that she “had to look skinny in order to look like a ballerina.”

“And I’ll tell you this – I’m not promoting this at all – but I used to be a smoker, and so I smoked a lot of cigarettes and I ate a limited amount of calories.”

In Dallas Buyers Club, Jared Leto gets in the skin of Rayon, a transgender woman with AIDS who befriends Matthew McConaughey’s character Ron Woodroof.

The actor and Thirty Seconds to Mars frontman lost more than 30 pounds for the film, and said that he “stopped eating” and had to change his “entire being.”

Playing Rayon, he explained, changed everything, including the way he walked, sat, and thought.

"It was 30 or 40 pounds," Leto told The Wrap about his shocking weight loss. "After a while, I stopped counting. It changes the way you walk, the way you sit, the way you think."

What constantly kept him motivated was a commitment to accurately represent his character.

“For me, it's not about the most weight I can lose, it's more to represent the character. I'm focused on what it means to be a transsexual woman."

The Canadian-American actress’s hair became increasingly damaged as she continuously bleached it white-blonde for her role as Number Six in Battlestar Galactica. For the second season of the show, the crew had to cut it shorter because it looked really unhealthy.

Over time, Helfer’s hair started falling out, which led to her wearing a wig.

She told TV Squad: "When we started the second season, every episode my hair got thinner and thinner and thinner, and shorter and shorter and shorter—and then finally it started falling out in chunks and they had to give me a wig."

Segel was “forced” to lose weight in order to play Emily Blunt’s love interest in the romcom The Five-Year Engagement.

The process of losing 35 pounds (15 kg) involved exercising on set and having someone closely watch the actor’s diet.

“I didn’t enjoy it. They sent a trainer to set, and I had to work out twice a day, and he would also watch me eat all day,” the How I Met Your Mother actor revealed during an interview with David Letterman.

However, he figured out a way to disobey the filmmakers’ request. Since he played a chef in the movie, he paid his co-stars “phenomenal amounts of money” to purposely mess up their lines so he could eat whatever was available on set.