The heartbroken actress - who was caught having an affair with Snow White and the Huntsman director Rupert Sanders - is not looking after herself properly as she comes to terms with the end of her relationship with Twilight co-star Pattinson, according to friends.

A source told Showbizspy.com: "Kristen is a nervous wreck and existing on a diet of cigarettes, sugar-free [energy drink] Red Bull and the occasional bag of potato chips.

"She's been hiding out at the Los Angeles home of a producer friend and is looking pale and worn-out.

“Whenever anyone tries to push her to eat even a small bowl of soup, she either claims that she's just had something, which isn't true, or that she's nauseous and there's no chance of keeping anything down.

"Kristen is grief-stricken and has hit rock-bottom. In many ways, Kristen living off cigs and Red Bull is a way of punishing herself."

Since they split in July, Stewart has been keeping a low profile, cancelling an appearance at the MTV Video Music Awards – which she was due to co-host with Pattinson – next month, and not appearing at the premiere of her latest film On the Road in London.

Meanwhile, Pattinson has made TV appearances to promote his new film, Cosmopolis, in the US, but dodged questions about Stewart, becoming flustered when asked about her on Good Morning America.

On the show, Pattinson – who had just been given a box of his favourite cereal, Cinnamon Toast Crunch – was asked what he wanted his fans to know about the situation in his personal life.

He stammered: "[My fans] seem pretty excited about... kind of whatever. Um, I'd like my fans to know that Cinnamon Toast Crunch is just 130 calories [a serving].

"Pretty much everything that comes out of my mouth is irrelevant."