Actors and actresses who love their craft have no problem making drastic weight changes for roles. They hope to achieve more realism by literally transforming into their characters.

Matthew McConaughey:
Matthew McConaughey: "Dallas Buyers Club"
Actor Matthew McConaughey played Ron Woodroof, an AIDS patient who gets involved with drug smuggling. Since McConaughey took on the role of a dying man, he and castmates like Jared Leto lost huge amounts of weight. McConaughey dropped 40 pounds by eating around 1,700 calories a day. "I ate my fish, my vegetables, and I had my wine," he noted to The Wrap about the transformation.
Robert De Niro:
Robert De Niro: "Raging Bull"
Back in 1980, Robert De Niro won the role of Jake LaMotta, a boxer with weight issues. To prepare for the role, De Niro traveled to France and Italy for the sole purpose of eating. He gained 70 pounds for the film, one of the biggest transformations at the time.
Vanessa Hudgens:
Vanessa Hudgens: "Gimme Shelter"
In this 2013 film, actress Vanessa Hudgens plays a pregnant teenager who becomes homeless. She decided to fully embody the role by packing on at least 10 pounds. At the time, she was in France for the Cannes Film Festival, so she didn't hesitate to binge on delicious French food. "It's not hard to put on weight in France when you're eating all the good French food," she said to People magazine.
50 Cent:
50 Cent: "Things Fall Apart"
Rapper 50 Cent acted in this 2011 film in which he plays a football player who develops cancer. He shed considerable weight for the role to look as though he was dying. In order to lose the pounds, he consumed nothing but liquids and also worked out daily for at least three hours.
Charlize Theron:
Charlize Theron: "Monster"
In this 2003 film, Charlize Theron plays a serial killer and prostitute. She also gained 30 pounds in order to embrace the role. According to Theron, she relied heavily on Krispy Kreme donuts to put on the pounds. Eventually, after she tired of the sweet treat, she moved on to consistently munching on chips.
Natalie Portman:
Natalie Portman: "Black Swan"
The already slim Natalie Portman lost 20 more pounds to play a ballerina named Nina in this 2010 film. To drop weigh for the role, she consumed no more than a few hundred calories daily. She also spent plenty of time training and learning to dance, at least five hours, six days a week.
Matt Damon:
Matt Damon: "Courage Under Fire"
Matt Damon had to lose around 40 pounds to play Specialist Ilario in this 1996 war tale. He did this by spending lots of time training and held himself to extreme calorie restrictions. He would consume little more than chicken, a baked potato, and egg whites and then run at least six miles daily. He lost so much weight that he had to work with doctors after filming wrapped to get healthy again.
Vincent D'Onofrio:
Vincent D'Onofrio: "Full Metal Jacket"
For this 1986 flick, Vincent D'Onofrio played Leonard Lawrence, a marine. Lawrence had weight issues, and D'Onofrio had to pack on some pounds for the role. Overall, he gained 70 pounds, which actually surpassed Robert DeNiro's weight gain for "Raging Bull".
Jared Leto:
Jared Leto: "Chapter 27"
In this 2007 John Lennon biography, Jared Leto plays murderer Mark David Chapman. To stay true to the character, Leto put on over 60 pounds to prepare for the film. He consumed plenty of ice cream as well as olive oil and soy sauce with his meals. Leto put on weight so quickly that he developed gout.
Anne Hathaway:
Anne Hathaway: "Les Miserables"
In the film remake of this musical, Anne Hathaway shed 25 pounds to play homeless prostitute Fantine. Perhaps she wanted to get into the depressive mindset of her character, for Hathaway says that she ate nothing more than lettuce. She had no strength, so at one point before she gained the weight back, she even broke her arm from a simple fall.
Tom Hanks:
Tom Hanks: "Philadelphia" and "Castaway"
Tom Hanks became scary skinny for two different films. In "Philadelphia," he played Andrew Beckett, a man with AIDS. Hanks wound up shedding 26 pounds for the role, but years later for "Castaway," he dropped even more weight, at least 60 pounds. It ultimately took him a year to shrink himself to waiflike proportions for the lost-at-sea film.
Christian Bale:
Christian Bale: "The Machinist" and "Batman Begins"
Christian Bale has transformed his body several times over the years for roles. In "The Machinist," he plays Trevor Reznik, a man with insomnia. Overall, Bale lost 60 pounds for the role and looked horrifyingly skinny. Shortly after, for "Batman Begins," he beefed up his regular frame with 40 extra pounds through weightlifting.