Reports say that Angelina Jolie is trying to shed 9.5kg in 21 days for a role in her new movie 'Salt'.
In the film, the actress plays a CIA assassin called Evelyn Salt who is forced to disguise herself as a man.
The shooting of the film has started in Washington DC, where she has been seen running through the streets of the city wearing a blonde wig for the role.
"To play a man convincingly Angelina is adamant she needs to lose her curves," News.com.au quoted a source, as saying.
According to friends, Jolie is so determined to look like a boy she has turned to the Martha's Vineyard Detox Diet to help shrink her already slender frame.
The extreme diet, which was popular in Hollywood in 2007, encourages followers to ingest liquids every two hours to 'cleanse the body'. Solid food is strictly prohibited.
According to reports, the 33-year-old started her detox three days before last month's Oscars and is already battling fatigue.
Another source told Britain's Grazia magazine, "She has been trying to go for the full 21 days but it's tough.
"She's lost around eight pounds (3.6kg) but is now introducing a couple of small meals in between shakes as she was starting to feel weak," the source added.
Jolie's role was originally intended for Tom Cruise, but the character was rewritten after he dropped out.