Christian Bale, of Batman fame, lost more than 60 pounds to play the lead in "The Machinist," which came out in 2004.
Charlize Theron gained 30 pounds to play convicted serial killer Aileen Wuornos in the 2003 movie "Monster." The South African actress won an Academy Award for her performance.
50 Cent dropped from 214 pounds to a scrawny 160, reportedly via a liquid diet and a hard-core workout regimen. He did it to look sickly for his role in the movie "Things Fall Apart," in which he plays a cancer-stricken football player.
Renee Zellweger gained almost 30 pounds to play the title role in the 2001 film "Bridget Jones's Diary." She shed the weight only to regain it for the 2004 sequel, " Bridget Jones: The Edge of Reason."
Matt Damon reportedly dropped 40 pounds to play a Gulf War veteran in the 1996 movie "Courage Under Fire." More recently, he beefed up to play an FBI whistle-blower in the 2009 movie "The Informant."
Tom Hanks lost about 50 pounds for his role in the 2000 movie "Castaway."
Beyonce lost about 20 pounds for her role in the 2006 hit movie "Dreamgirls." She used a liquid diet but doesn't suggest that other people follow her lead, according to People magazine.
Robert De Niro
Robert De Niro gained a whopping 60 pounds to play aging boxer Jake La Motta in the 1980 classic "Raging Bull."
George Clooney gained gobs of weight to play an out-of-shape terrorist hunter in the 2005 film "Syriana."
Colin Farrell lost weight for the 2009 film "Triage," in which he portrayed a war-weary photojournalist.