For his role in The Machinist, Christian Bale lost nearly 65 pounds, maintaining his frail frame by eating only 275 calories a day over the course of four months (the suggested daily caloric intake for men is between 1,500 and 2,000). The 121-pound actor then bulked up to 190 in just five months so that he'd be in appropriate superhero form for filming Batman Begins (Bale eventually gained an additional 30 pounds as the Dark Knight). "It was like a massive shock to my body because of what I was trying to get it to do," said Bale in an interview with the BBC. "My metabolism had to get back up to speed, because my heart had gotten used to a whole different way of living." On the flipside, actress Renée Zellweger gained excessive pounds for the popular Bridget Jones's Diary, going from a size 4 to a size 14. The physical and mental strain of eating 4,000 calories a day then dropping the weight postproduction was enough to make the actress question signing on for the Bridget Jones sequel.
The bottom line? Don't try this at home.