Christian Bale (Lost 63, Gained 100, Gained 40)
Credit: Everett

Behold the king of the shape-shifters. He got ripped to perfection for 2000's American Psycho, then lost 63 pounds (on a diet of apples, coffee, and cigarettes – reportedly less than 500 calories a day) for 2004's The Machinist, where his heart can be seen beating through his chest. Physically embodying Batman, which came out the following year, wasn't easy: "I did actually start to feel I was putting my body under too much pressure because I put on 100 pounds in five months," he's said. When it came to playing welterweight crack addict Dicky Eklund in 2010's The Fighter, he knew he couldn't lose 60 pounds and still be able box, so he slimmed down "to what looked like might be the right body type" then relied on makeup for extra gauntness. Bale was less cautious when it came packing on more than 40 pounds of gut for American Hustle. "I literally ate anything that came my way," he's said. As for how his ups and downs affect his off-screen life, he noted, "I'm grateful to have a very patient and loving wife."

The Bottom Line:
Even if weight cycling doesn't lead to lasting metabolic changes, Bale did feel short-term effects during his transformation from frail to buff: "My metabolism had to get back up to speed because my heart had got used to a whole different way of living for some time."