22 Unbelievable (and Crazy) Movie Transformations (PHOTOS)

Natalie Portman had to slim way down to play a psychologically disturbed ballerina in Darren Aronofsky’s 2010 thriller Black Swan, a riveting performance that won her the 2011 Best Actress Oscar. Natalie ultimately dropped 20 pounds for the movie, swimming and practicing ballet for up to 8 hours a day, six days a week. "I had never gotten that much training — to be doing five-to-eight hours a day of [it] was really a challenge," Natalie revealed to Us Weekly.

For her edgy role in the film, Mila Kunis also shed 20 pounds — a drastic transformation she now regrets. "When I got down to 95 pounds, I was muscles, like a little brick house, but skin and bones," she told Harper’s BAZAAR. "When I gained it back, it went to completely different areas. [...] All the weight that left my chest went to my side hip, my stomach."

Her body "has never been the same," but that's not to say she wouldn't do it again. "I'm not going to say I'd look forward to it, but if an offer came along, I'd do it," she admitted.