No, she is not anorexic, but like most skinny women in Hollywood she just doesn’t eat.

Keira Knightley says she is not anorexic
LONDON – Oscar-nominated actress Keira Knightley disclosed a family history of anorexia Tuesday but said that she doesn’t suffer from an eating disorder.
The slender 21-year-old, in London to promote “Pirates of the Caribbean: Dead Man’s Chest,” rejected suggestions that she suffers from an eating disorder, which surfaced after she appeared at the film’s premiere in a revealing gold Gucci gown.
“I’ve got a lot of experience with anorexia ó my grandmother and great-grandmother suffered from it, and I had a lot of friends at school who suffered from it,” Knightley said. “I know it’s not something to be taken lightly and I don’t.”
She said she was surprised by any suggestion that she had an eating disorder.
“(The press) said to me yesterday `How does it feel to be called anorexic?’ and I had no idea that I was,” Knightley said. “I’m not saying there aren’t people in the film industry that suffer from it, because I am sure that there are. But I’m quite sure I don’t have it.”
Knightley, who was nominated for best-actress for her role in “Pride and Prejudice”, said she welcomed discussion about the illness.
“In a way it’s good that it’s out there and that people are talking about it,” she said.