At Hong Kong Baptist Hospital, paediatric consultant Dr Lilian Wong also says she is seeing younger patients with eating disorders.

A report co-authored by Lee in the International Journal of Eating Disorders last year said the number of Hong Kong patients suffering from anorexia nervosa or bulimia had doubled over 20 years at a psychiatric clinic they studied. In the first 10 years, the clinic saw 67 patients; during the next decade, from 1998 to 2007, the number rose to 128.

Because sufferers don't fit the usual criteria for diagnosis (female, 13 to 20 years old), doctors have coined a new term - 'eating disorder not otherwise specified' - for the condition in young children.

Parents may not notice unusual behaviour in their children, such as routinely skipping meals, bouts of bingeing and purging, for months, Wong says. Early diagnosis and intervention, however, is crucial for successful treatment.

'Parents often bring their children in after eight to 13 months of symptomatic behaviour,' Wong says. 'When this occurs, the child may be at 75 per cent of their ideal weight or have a BMI [body mass index] of 12-14 per cent and, at this point, recovery without relapse is harder to predict.'

That's why Lee and his colleagues set up the Hong Kong Eating Disorders Association 10 years ago. Besides acting as a support group for patients and their families, the association runs increasingly popular media and body image workshops in local schools. These are preventive measures: students are taught to differentiate media messages and learn to accept themselves while strengthening positive qualities such as humour or compassion.

Joanna, whose daughter was diagnosed with anorexia nervosa at 17, says the association's work in parental support helped save her child. Problems surfaced after her daughter left to study overseas.

'We sent her to live with relatives in the US while attending school, thinking it was a great opportunity for her. Looking back, we were probably wrong,' recalls Joanna, now an active volunteer with the association.

'We started to notice a weight change, but it was slow at first. In the first six months abroad, she lost 4.5kg.'

When the teenager came home for a visit after eight months, she had lost 9kg. Understandably concerned, Joanna and her husband took her to a doctor but he couldn't find anything wrong with her. 'When I think back it wasn't just the weight that was the problem - she was terribly moody and her eating patterns were unusual. Parents need to know it's not just the weight that changes,' Joanna says.

Remarkably, the girl maintained high grades throughout her studies but her health continued to deteriorate over the next year, prompting the relative who was looking after her to call Joanna.

'She told me my daughter had lost five more kilograms and that she was exhibiting strange behaviour: never finishing meals and cutting up her food into tiny pieces,' Joanna says. 'Of course, I now know that these are stalling techniques used by sufferers to avoid eating.'

Just after her second Christmas away from home, Joanna's daughter called to say she wanted to return home. 'When I saw her at the airport I couldn't believe my eyes. She weighed about 36kg and she couldn't smile - when she did it was just terrible. There was hardly any flesh on her face.'

They enrolled her at the American International School, where a counsellor recommended 'wrap-around treatment' that involved family, doctors, psychologists and friends in the patient's recovery. With their help, Joanna's family worked to 'pamper' the teenager; she regained most of her weight after six months and was largely recovered after about a year.

'She graduated from university this year and will begin a job in London soon. I learned that, in order to get through it, you have to open up your heart and overcome your fears.'

Joanna continues to attend monthly parental support groups, volunteering as a mentor for people who are helping their child deal with eating disorders.

Parents are a key to the youngsters' recovery, she says, as 'we really are best at supporting the children through this terrible illness'.

This is an edited version of an article which appeared in the South China Morning Post on January 5