"This kind of speculation can be less than constructive, " said a spokeswoman for the organisation Bodywhys. "It tends to be couched in terms that oversimplify disorders by reducing them to issues around appearance. Every time this stigma is reinforced, people are going to find it more and more difficult to look for the help they need."

Knightley's appearance sparked a series of media reports suggesting the 21-year-old actress is anorexic, something she hotly denied.

"Whatever people say about my weight, they are all wrong, " she said, revealing that anorexia has run in her family in the past. "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. I know it's not something to be taken lightly and I don't."

Knightley is just one of a long line of celebrities who are speculated to have suffered from eating disorders, including Lindsay Lohan, Mischa Barton and Calista Flockhart.

Nicole Richie, whose weight was the topic of a concerted media campaign, recently admitted she suffers from anorexia and was seeking help.

"Any reporting around eating disorders needs to recognise the enormous complexity of eating disorders and be respectful of the dignity of the individuals affected, " said the Bodywhys spokeswoman. "Sensationalist reporting can feed the myth that people with eating disorders are attention-seeking. There is stigma associated with eating disorders, much of it due to ignorance."

This is not the first time Knightley's weight has come up in the press and she has said she gets hurt when critics say she is starving herself.

According to Bodywhys, up to 200,000 people in Ireland have an eating disorder and how the media report it is of utmost importance.

"The majority of people are not 'super thin' and yet the celebrity culture that prevails at the moment continues to send out the message that being super thin attracts attention and adulation, " said the spokeswoman, adding that Bodywhys had seen an increase in eating disorders among children in Ireland.

Bodywhys welcomed the recent Dove cosmetics campaign, which they said was expanding the very limited images of feminine beauty portrayed in the media.

"If reporting is carefully thought out to alert people to the dangers of the cult of thinness and presents the issue of eating disorders in a way that can contribute to building resilience against such a cult, then it is more likely to have a positive effect, " the spokeswoman said.