Oscars favor extreme weight loss or gain — but is it acting?

In “The Fighter,” Christian Bale is as thin and wan as the smoke from his character’s crack pipe. But radical weight loss is nothing new for the Oscar nominee — he shrank his 6-foot frame to an emaciated 121 pounds to star in the 2004 film “The Machinist.”

Going gaunt isn’t only for hard-core method actors. To attain a ballerina’s boniness in “Black Swan,” the petite Natalie Portman reportedly dropped 20 pounds — and also earned an Oscar nom.

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(Nicolas Gellar /PARAMOUNT CLASSICS ) - Christian Bale shrank to 121 pounds for his role in ”The Machinist.”

Stars who starve always get attention in movie acting and are also a good bet for Oscar notice. To play concentration-camp victims, both Adrien Brody (in “The Pianist”) and Meryl Streep (in “Sophie’s Choice”) drastically lost weight — and gained Oscars. But if starvation has become its own acting technique, so has fattening up. Think of Robert De Niro’s Oscar-winning bloat in “Raging Bull,” Charlize Theron’s Oscar-winning stoutness in “Monster” and Renee Zellweger’s Oscar-nominated curves in “Bridget Jones’s Diary.”

On the face of it, extreme physical transformation seems to underscore an actor’s seriousness, and the backstory of cheeseburger-overload or puritanical self-deprivation helps sell the movie. When Portman was doing the publicity circuit for “Black Swan,” interviews centered on the severity of her weight-loss regime and workouts. “You don’t drink. You don’t go out with your friends. You don’t have much food,” Portman told Australia’s Sunday Telegraph magazine. “You’re constantly putting your body through extreme pain and you really understand the self-flagellation of a ballet dancer.”

But does slimming down or beefing up have artistic merit? Does it contribute to great acting?

Some observers decry the practice and see the Academy Award attention that an actor’s appearance gets as part of a misguided benediction of movie stars who de-glamorize in pursuit of their art.

“Oscars have often gone to people who do something to themselves,” says film historian and Wesleyan University professor Jeanine Basinger. “But the idea that gaining or losing weight has anything to do with acting is, to me, utterly insane.”

Author and film critic Molly Haskell agrees. “Since time immemorial, the Oscars worship this kind of self-transforming, where you become someone almost unrecognizable,” she says. “Acting is supposed to be about using the imagination, creating a character with your imagination, but you get stuck in the visual of it, and how brave it is for this beautiful woman to make herself ugly. It’s a kind of vulgar idea of what acting is.”

Haskell equates Bale’s seesawing weight (after “The Machinist,” he packed on 100 pounds for “Batman Begins”) to a stunt. “He must just like to do this,” she says. “I like him in ‘The Fighter.’ I think it’s an interesting performance — over the top, but interesting. But I don’t think he needed to do the weight-loss to do it.”

Yet slimming down to play drug-addicted ex-boxer Dicky Eklund must have seemed like second nature to Bale. His sinewy look in “The Machinist” gained considerable attention; the Los Angeles Times praised his “assuredly disturbing effect.” But it came as a surprise to Brad Anderson, who directed the dark psychological thriller about a factory worker consumed by guilt. The script described the title figure as “a walking skeleton,” says Anderson in a recent interview, but when the frail Bale showed up on the set, his appearance stunned the cast and crew.