Mila Kunis has revealed she ate "very little" while preparing for her role in Black Swan.

The actress sat down with her co-star Natalie Portman to celebrate the film's 15-year anniversary for an interview with Vogue.

As the pair discussed their preparations to play rival ballet dancers, Kunis admitted it was a gruelling process.

"My prep was a lot of dancing and very little eating - which I know you're not supposed to say, but it's the truth. I drank a lot of broth and danced for 12 hours a day," the 42-year-old star recalled of the movie, directed by Darren Aronofsky.

"We were only supposed to have three months of prep before filming started, but we lost some financing, so that got extended to six months while Darren tried to find money."

Kunis went on to explain how shooting complex dance scenes for the 2010 drama took their toll on her body in other ways.

She continued, "We would shoot those dancing scenes for hours, and I had bruises all over my ribs just from being lifted over and over again."

Elsewhere in the interview, Portman revealed she had urged Aronofsky to cast her friend Kunis as ballerina Lily after realising the actress had ballet experience.

However, Kunis joked that Portman was so keen for her to land the role that she had been overly generous about her dance skills.

"I think I said, 'I danced once,' and that got twisted into me having taken pointe," Kunis laughed, to which Portman admitted, "I may have exaggerated on your behalf!"