Some stars go to great lengths to get into character. Matthew McConaughey, Anne Hathaway, Renee Zellweger, and Christian Bale are just a few of the many celebrities who've lost or gained significant amounts of weight for movies
Natalie Portman in Black Swan
The already-slim star underwent a major physical transformation to play the lead role in 2010's Black Swan, for which she won the Best Actress Oscar. "I think it was just the physicality of it all that was the most extreme," she told Us Weekly of preparing for the film. "I mean, I had never gotten that much training -- to be doing five to eight hours a day of it was really a challenge."