The 'Twilight' star - who is still in hiding after boyfriend Robert Pattinson walked out of their home - has become a "nervous wreck" and is "living off a diet of cigarettes, Red Bull (energy drink) and crisps", reported Showbiz Spy.
"Kristen is a nervous wreck and existing on a diet of cigarettes, sugar-free 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," said a source.
The source also said that the star was so "grief-stricken" that even when she tries to eat she gets sick.
"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," they continued.
"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."