Portman tells of the agony she endured to be a dancer

The actress Natalie Portman has revealed that the punishing schedule she endured for her new role as a ballerina in Black Swan left her fearing she was going to die.

The waif-like 29-year-old lost 20lb for the role, eating little more than carrots and almonds on a punishing diet, and spent eight hours a day in rehearsals. Ms Portman, who is hotly tipped for an Oscar for her portrayal of the desperately ambitious, perfectionist dancer, said: "There were some nights that I thought I literally was going to die."

In a week when she announced she was pregnant and engaged to marry her Black Swan choreographer, Benjamin Millepied, she told Entertainment Weekly that the film left her physically and emotionally drained: "It was the first time I understood how you could get so wrapped up in a role that it could sort of take you down."

The actress, who dislocated a rib during rehearsals, said recently: "All dancers are always dancing with an extreme injury. Not just a sore muscle, they're dancing on a sprained ankle or with a twisted neck or something.

"You'll see them do incredible stuff and then limp off stage, straight to a bucket of ice. Part of the art is hiding all the pain."

The film, which is due to open in Britain this month, has received mixed reviews from ballerinas. Racheal Prince, of Ballet British Columbia, said she thought Ms Portman's character was exaggerated. "She's anorexic, bulimic, crazy," the 26-year-old dancer said. "I'm sure every dancer struggles with little things here and there, but for one girl to struggle with every single problem out there, it just makes us look crazy."

British ballerina Gillian Murphy, a principal dancer with the American Ballet Theatre, also criticised the film for its "shocking and disturbing" portrayal of the ballet world.

Director Darren Aronofsky insisted he had had equally positive responses."So many dancers are incredibly relieved that there's finally a ballet movie that takes ballet as a serious art and not just as a place to have a love affair,'' he said, nevertheless admitting that the film was punishing to make.

"There was really no money for the film and we had to push, a lot of times. And I only found out recently that the person who suffered most from pushing was Natalie, just living on carrots and almonds.''

The ballet world has fought for years to counter accusations that it turns a blind eye to eating disorders.

The Royal Ballet School's nutrition policy 2010 insists that it monitors students to ensure that they maintain a healthy weight. A statement agreed by all schools operating under the Department for Education's Music and Dance Scheme reads: "It is known that, along with many athletes, dancers are at greater risk of developing eating disorders and associated medical problems, than the general population... All dance schools within the MDS scheme are committed to developing, training and nurturing healthy dancers. Schools endeavour to encourage positive attitudes towards weight control, healthy eating and body image at all times."

Black Swan, however, is likely to re-ignite the debate, drawing comparisons with the fashion industry.

Actors who made the weight

Russell Crowe

Crowe gained 40lb for his role in The Insider (1999), by eating cheeseburgers and cupcakes. He then shaped up to shoot Gladiator. By 2008, Crowe had gained 63lb for Body of Lies, then slimmed down in 2010 for Robin Hood.

Renee Zellweger

Zellweger's fluctuating weight dates from her starring roles in the Bridget Jones films, for which she gained nearly 30lb. She also attracted controversy for her thin appearance in roles such as Roxie Hartin Chicago.

Tom Hanks

For his role in Cast Away (2000) Hanks first gained weight to shoot the opening scenes, then spent a year away from the set losing 55lb and growing a flowing beard to appear as a castaway. His weight loss coach was mentioned in the film's credits.

Mickey Rourke

Rourke slimmed down from his usual 192lb for his professional boxing career in the early 1990s, reaching 167lb. After returning to acting in 1995, he gained 68lb for The Wrestler (2008), which was nominated for two Oscars.

Robert De Niro

De Niro gained 60lb for his role as Jake LaMotta in Raging Bull (1980). According to director Martin Scorsese, production of the film was put on hold for four months so De Niro could binge in Italy and France, increasing his weight from 145lb to 215lb.

Christian Bale

Adopting a crash diet of coffee and apples, Bale reduced himself to a skeletal 121lb for the 2004 psychological thriller The Machinist. Astonishingly, he then immediately bulked up to play Batman, reaching 230lb in six months.