Looks like Jake Gyllenhaal is the latest in a long line of celebs to drop a pretty shocking amount of weight for a role. In recent days, Gyllenhaal has been spotted filming the movie "Nightcrawler" in Los Angeles, looking downright frail. I love the dude's bone structure, trust, but those cheekbones are positively skeletal. Lest you think he's playing a drug addict or, I dunno, cancer patient in the film, he's actually portraying a journalist who stumbles upon some underground crime ring. You know us writers -- so malnourished! So, what other celebs have gone to dieting extremes for the sake of their craft? Who lost the most? How did they do it? Click through to find out!