This year, Anne Hathaway is favored to win Best Supporting Actress for her role as Fantine, the single-mother-turned-prostitute, in Les Misérables. As most fans now know, she lost 25 pounds for the part and she did so by nearly starving herself, subsisting at some point on nothing more than “two thin squares of dried oatmeal paste.” That level of commitment should help her win an Academy Award, just like it did when an already wispy Natalie Portman lost twenty pounds for her Oscar-winning turn as the unhinged ballerina in Black Swan. Or like it did when Charlize Theron packed on 30 to play serial killer Aileen Wuornos in Monster. Or like it did when scrawny Hilary Swank hit the gym and packed on sixteen pounds of muscle for Million Dollar Baby and basically changed her gender for Boys Don’t Cry.

Acting is a physically demanding profession, and never more so than when an actress undergoes the kind of corporal transformation to embody her character. I’m not just playing Fantine; I am Fantine. Many critics argue that actors and actresses change their looks as a ploy to win Oscars, an attempt at fooling the Academy that they are truly gifted and committed. It’s also a way for beautiful people to show that they are more than just a pretty face. Plus, it’s easy for audiences and judges to get caught up in the physical work, so changing your shape is an effective way for these women to draw attention to their performances.

So, of course, it’s hard not to see a bit of calculation behind an actress’s decision to put her body through the rigmarole, especially when you look at the success stories. Theron, Swank, Portman, and Kidman have changed their looks drastically, won, and gone on to become megastars since 2000. Michelle Williams gained fifteen pounds for Blue Valentine, but lost to a more transformed Portman; same with Renée Zellweger in Bridget Jones’s Diary who lost to a uglified Halle Berry in Monster’s Ball. (That doesn’t mean all actresses who go the distance get the Oscar nod. Just ask Gwyneth Paltrow, who gained twenty pounds to play a country music train wreck in Country Strong or Beyoncé, who lost twenty to play Deena Jones in Dreamgirls.)

Win or lose, these diets quickly become part of any studio’s Oscars campaign. Of Hathaway’s 25-pound drop, Les Mis director Tom Hooper told the the Los Angeles Times: “To be honest, I thought she was going further than she should, and I tried to discourage her.” That sounds almost exactly like what Darren Aronofsky told Access Hollywood about Natalie Portman’s prep for Black Swan: “At a certain point, I looked at [Natalie’s] back, and she was so skinny and so cut … I was like, ‘Natalie, start eating.’ I made sure she had a bunch of food in her trailer.” Sure. Hollywood is ruthless when it comes to image, so if an actress — who otherwise earns her bread and butter by looking beautiful in big budget blockbusters, magazine covers, and perfume ads — is going to put herself through the pain of manipulating her image, she’ll want to win something for it.

But these are awards given to celebrate the craft, so what is it about getting skinnier or fatter that suggests good acting? “The actor’s creativity is really two fields: it’s the imagination and the body,” says David Krasner, author of An Actor’s Craft: The Art and Technique of Acting. “There are only so many things that I can pretend that I’m not, [so] if I can actually be heavier, that’s one thing off the to-do list. The closer you can get to being real, the better actor you are.” Getting skinny isn’t just about convincing people you’re going for it, it’s about showing them you’re an incredible talent, too. Just imagine what Dior’s version of Charlize Theron would’ve looked like in Monster. It wouldn’t work.

Today, audiences expect and enjoy a degree of realism in the movies. When Jennifer Lawrence was cast as Katniss Everdeen in the Hunger Games, fans worried that Lawrence wasn’t skinny enough for the part. Even Manohla Dargis complained in the New York Times: “A few years ago Ms. Lawrence might have looked hungry enough to play Katniss, but now, at 21, her seductive, womanly figure makes a bad fit for a dystopian fantasy about a people starved into submission.”

This sense that movies should feel real started in the fifties and has been slowly evolving ever since. “We used to go to the movies for fantasy, to get take us away from everyday life,” says Turner Classic Movie host Robert Osborne, who also wrote 80 Years of the Oscar: The Official History of the Academy Awards. “The women all looked like Katharine Hepburn or Carole Lombard and the men all looked like Cary Grant or Robert Taylor.” Now, we want people to really look like the taxi driver or the waitress at the corner deli, he says. (This also means that we want our ballerinas to look anorexic and our downtrodden victims in eighteenth-century France to be near death.)

At about the same time that movies were getting hit with reality, there was a similar revolution taking place in the studios where young actors trained. Constantin Stanislavski’s method, which he started developing in turn-of-the-century Russia, had gained a following in America in the fifties. Actors became focused on capturing the emotional and physical aspects of the their characters, and famous American teachers like Lee Strasberg and Stella Adler continued to build on that philosophy. Among the new wave was Marlon Brando, who according to Krasner, was the first actor to really bring method to the big screen, injecting into his characters a physicality that was fresh.

In 1980, when Robert DeNiro put on 60 pounds to embody boxer Jake LaMotta in Raging Bull, he was thought of as first actor (male or female) to drastically alter his appearance for a part. He won an Oscar for the role. And in 1982, Meryl Streep dropped 25 pounds for her role in Sophie’s Choice. Since then, the number of men and women who have undergone extreme physical transformations for roles they deem Oscar-worthy seems to be gradually increasing — it becomes an annual event that we’re reminded of each month on magazines and blogs that culminates during red-carpet season.

In an interview with USA Today in 2004, Renée Zellweger, who put on 30 pounds to play chubby Brit Bridget Jones, complained: “What’s interesting is why the fixation … It’s such an infinitesimal part of the characterization. I mean, who cares?” She went on to ask whether men had to suffer under the same scrutiny. And although there has been quite a bit of discussion about the way men manipulate their bodies (remember Christian Bale in The Machinist?), it never feels quite as loaded. That’s especially true when an already-skinny actress like Hathaway or Portman drops more than twenty pounds for a role. Aren’t they already thin enough? Also when we tell a plumper Zellweger that she looks better than ever.

But even as we critique their methods, we can’t help but feel mesmerized by the stars’ seemingly magical ability to manipulate their figures in ways the rest of us never could. Actresses may be going for realism onscreen, but in the real world, they’re living in the Hollywood fantasy.