Reese Witherspoon says Wild role was 'hardest' of career

Witherspoon plays the lead role in Wild and also co-produced the film

Hollywood star Reese Witherspoon has said her new film Wild was the most challenging of her career to date.

The Oscar-winning actress plays a young woman who goes on a 1,100-mile hike across the Pacific Crest Trail after the break-up of her marriage.

Based on the memoir by Cheryl Strayed, Witherspoon's role involves scenes of explicit sex and drug taking.

"It's the hardest I've ever done for many different reasons," Witherspoon told reporters in London.

"The physicality was really difficult, but after that was the emotional part of it," she continued ahead of the film's European premiere.

"The sex scenes were the hardest thing for me to do. I've never had to do anything like that in my entire life.

"I had to do all the parts of the movie, the parts that made me feel uncomfortable too, because it is about emotional honesty," the 38-year-old went on.

The actress, who also co-produced the film, has been tipped as a frontrunner for next year's best actress Oscar.

She previously won the award in 2006 for her role as Johnny Cash's wife in Walk the Line.

Wild shows Witherspoon's character carrying a heavy backpack on a gruelling 94-day journey of self-discovery across hot desert and icy mountains.

The actress revealed the backpack had originally been filled with newspaper, only for director Jean-Marc Vallee to exchange it for a heavy load to make her movement look more realistic.

The actress's performance could see her in the running for a second Oscar

Witherspoon told the BBC News website that she had benefitted from having the real Cheryl Strayed on set during filming.

"In some ways I was a little scared that she would be watching and judging me. But it would actually help me get into the scene."

Strayed said on Monday that many of the conversations she had with Witherspoon had not been about the making of the film.

"They were about our lives, our childhoods and relationships, talking about ourselves as mothers - everything from the mundane to the extraordinary," she told the BBC.

"There was some [talk] about how to hook up the backpack, but the more important work was opening ourselves up to each other."

British novelist Nick Hornby, who wrote the film's screenplay, said Wild could not be described as a so-called "chick flick".

"It's about grief and heroin addiction and promiscuity and being really tough physically and mentally," said the Fever Pitch and High Fidelity author. "So it's not really like any chick flick I've ever seen."

Wild has its European premiere at the BFI London Film Festival later and is released in the UK on 16 January.

Vallee's previous film, Dallas Buyers Club, won Matthew McConaughey and Jared Leto acting Oscars earlier this year.