Nicole bulks up on the Bridget Jones diet

And like Renee Zellweger before her, it's all for her art.

Just as Renee had to bulk up to play Bridget Jones, so Nicole has already put on 10lb for her latest film, The Reader.

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And the 40-year-old Australian actress is planning to double her weight gain in the coming weeks, according to sources on the movie, in which she stars alongside Ralph Fiennes.

"Nicole has said this is one of the most challenging film roles of her career," a close friend said.

"She is naturally very slim and loves to run and swim so she is always very toned.

"The part she plays demands that she gets fatter throughout the movie as her character slips into middle age.

"It's a very demanding role because there are a lot of explicit lovemaking scenes.

"The film is set over several decades so her character changes a lot.

"Nicole was originally planning to use prosthetics but was told by the director, Stephen Daldry, that it would be more realistic if she gained the weight."

The star plays Hanna Schmitz in the adaptation of the bestselling German novel The Reader, which deals with the emotional repercussions of the Holocaust-in post-war Germany.

It tells the story of Michael Berg, a 15-yearold boy who has a passionate affair with older woman Hanna in 1958.

But Hanna disappears suddenly and Michael sees her again only years later when she is on trial for a war crime after it is revealed she was an SS camp guard.

Nicole's calorie-rich diet includes drinking daily protein shakes and ensuring carbohydrates are in every meal.

"She has been eating about four meals a day," said the friend. It's not usual to see her work her way through a big plate of pasta, with bread, and then a dessert.

She's having to gorge herself. She has quite enjoyed gaining the first 10lb and has been having lots of her favourite puddings as well as chocolate.

"Nicole loves her new bosom, but she is finding eating so much makes her lethargic and sleepy.

"She's usually running on adrenaline and has to be reminded to eat a meal. Now she's eating four, and sometimes five small meals a day."

The recent weight gain led to speculation that the actress was expecting her first baby.

The Oscar-winner was snapped this month in a tightfitting white dress in New York sporting what looked like a baby bulge and a bigger cleavage.

"Nicole usually has a flat stomach so when she was pictured looking more curvy, everyone thought she was pregnant," said the source. "In fact, she has been putting on weight and has had to buy bigger clothes."

The actress follows in the steps of Zellweger, who piled on 30lb to play Bridget Jones in two movies by eating a diet of pizza, peanut-butter sandwiches and fast food and drinking Guinness.

She ballooned from a dress size six to 14 before dieting back to her normal weight.