The sacrifice an actor is willing to offer

Matthew McConaughey lost fifty pounds for the role of an HIV-positive Texas electrician Ron Woodruff  in The Dallas Buyer's Club.

Jared Leto put on 62 pounds to play John Lennon's killer David Chapman in Chapter 27.

Robert De Niro in Raging Bull. He gained 70 pounds to play Jake LaMotta at the end of the film.

Charlise Theron gained weight and lost her make up for her role as serial killer Aileen in the film Monster.

Christian Bale in The Machinist and Batman Begins . In less then one year. 

To play IRA hunger striker Bobby Sands in  Hunger, Michael Fassbender lost  42 pounds and he had 170-pound before that. 

George Clooney put on about 35 pounds to play obese CIA operative Bob Barnes in Syriana. 

Production on the 2000 film Cast Away waited for a year so that Tom Hanks could lose over 50 pounds and grow out his hair.

When Jude Law filmed Dom Hemingway he gained 24 pounds, and had his receding hairline even more accented.“He was drinking, like, 10 sodas a day, drinking nonalcoholic beer, which is disgusting, and he was pasty-faced [from] smoking," said director Richard Shepard

In Tropic Thunder, Robert Downey Jr. plays a white actor who undergoes surgery to play a black Vietnam-era Army sergeant. He didn't do exactly that but the transformation is still impressive