Keira Knightley's mother has attacked 'playground bullies' for a whispering campaign suggesting the 23-year-old actress is anorexic.

Sharman Macdonald said her daughter has merely inherited a naturally slim physique from her father, 62-year-old theatre actor Will Knightley.

She said that her daughter never had to diet but instead followed a special eating plan - high in protein and carbohydrates - to keep weight on.

Enlarge 

Skinny minnie: Keira Knightley's mother Sharman MacDonald says her daughter is healthy, but naturally skinny

Eating plan: Keira when put on an eating plan to play Guinevere in King Arthur

Miss Macdonald, 57, claimed the actress must 'eat like a horse' to keep herself at a healthy weight.

She said: 'She has always been thin. She's her daddy's daughter, with his long body.'

The playwright explained that Miss Knightley was given an eating plan to bulk up for the role of Queen Guinevere in 2004 film King Arthur.

However, the plan called for her to eat less than she normally did and had to be abandoned after she lost weight.

The result was that posters intended for the U.S. market showed Miss Knightley with a digitally-boosted bust.

Her mother added yesterday: 'It's a playground situation that we're looking at with the Press - it's a form of bullying - but what can we do?'

In 2006, Miss Knightley denied rumours that she had an eating disorder.

She said: 'I've got a lot of experience with anorexia - my grandmother and great-grandmother suffered from it, and I had a lot of friends at school who suffered from it, so I know it's not something to be taken lightly and I don't.

'But I don't have it, I am very sure of that.'

Skinny genes: Keira's parents Sharman and Will

Last year the Atonement star admitted to visiting her GP for advice on how to gain weight.

She said: 'I went to the doctor to be checked out and asked him what I could do to put on weight.

'He told me that, for someone of my body type to get to a size 12, I would have to eat a lot of s*** food, stop exercising and drink loads.

'Basically, my body type is naturally thin. There is nothing I can do about it.'

Good friend: Sienna Miller, who will appear alongside Keira in The Edge of Love, says her pal has a hearty appetite

The actress will next appear on screen alongside Sienna Miller in The Edge of Love - a film about Welsh poet Dylan Thomas.

During film, her co-star testified to her friend's hearty appetite.

Miss Miller said last year: 'She is a really good friend of mine, she is a wonderful girl. Eats like a pig for everyone out there who calls her anorexic.'

The film will have its premiere at the Edinburgh film festival on Wednesday.