YOUNG women who document their weight loss by posting "selfies" showing their thinning frames are fuelling dangerous eating disorders, a leading expert has said.

Dr Alex Yellowlees from the private Priory hospital group in Glasgow said competitive selfie dieting 'diaries' were contributing to damaging psychological pressures that exacerbate anorexia and other potentially fatal illnesses.

He said: "Some people will take repeated pictures of themselves at various stages of their illness, and send them to others.

"They want to keep a record of their illness and see for themselves, as it were, the progress they think they are making towards anorexia, but they will also transmit the images to other sufferers on occasions."

Dr Yellowlees, medical director and consultant psychiatrist of Priory Hospital Glasgow, said the trend of sharing selfies was growing because of boom in social media sites which have become the core forum for interaction between young people.

In some cases, he said, young women were encouraged to reduce their weight to dangerous levels by looking at so-called "thinspiration" websites where they can compare their bodies with those of other extreme dieters.

Thinspiration websites can include blogs written by extreme dieters who upload their "tips and tricks" to encourage others to lose weight.

Dr Yellowlees said pro-anorexia websites, some of which display photographs of brittle-looking legs, concave stomachs and protruding ribs, were "particularly malignant".

Some sites, and hashtags, encourage the pursuit of the "thigh gap", when women try to become so thin that their thighs do not touch even when their feet are together.

Disturbing photographs and internet blogs are often accompanied by messages such as "food is the enemy" and "starving for perfection" to encourage women to their diets. One site, for example, suggested that grumbling stomach noises were in fact "applause" for self-starvation.

Dr Yellowlees said: "These sites are definitely still active. They may not as prevalent as they were, but they are still an active form of communication."

In addition, technology such as smartphone apps which can lead users to become obsessed with counting calories consumed and burned through exercise, which experts fear can seriously escalate the suffering of those with eating disorders.

The Priory Group is the UK's largest provider of eating disorder treatments outside of the NHS. It has seen a 15 per cent rise in adult patients admitted with eating disorders over the last year, increasing from 463 in 2013 to 535 in 2014.

Most patients were aged 18 to 25 but the largest increase was among adults aged between 36 and 45, with admissions in this age group almost doubling year-on-year.

In addition, the Priory admitted 139 children and young people between the ages of 11 and 17 last year for treatment, up from 87 in 2013.

Dr Yellowlees said: "Eating disorders are like a form of 'psychological malignancy' and should be taken very seriously by society. This includes anorexia nervosa, bulimia nervosa and binge eating disorder. The latter is more common as people get into adulthood and is linked to depression."

He added: "We live in a society which idealises thinness and is obsessed with dieting, size and shape. Society needs to recapture the truth that our real value and worth is not reflected in our clothes size but in our personal qualities and relationships with others."