The number of Kiwis getting medical intervention for eating disorders has increased by more than 40 per cent in the last five years.
But sufferers' families say there are still not enough hospital beds to keep up with demand.
In 2011, Ministry of Health-funded specialist services treated 894 people who were critically unwell through illnesses such as anorexia nervosa, bulimia nervosa and binge eating disorders.
Last year, 1290 New Zealanders with severe eating disorders were treated through these services.
Four years ago the ministry said the number of beds in hospital mental health wards and residential facilities for people with severe eating disorders had increased from 12 to 27 since 2009.
Today however the ministry says it doesn't know how many beds are allocated specifically to people battling eating disorders as its data does not identify mental health beds by diagnosis.
District health boards in the Northern and Midlands regions - stretching from Cape Reigna to East Cape - have access to a nine-bedded specialist eating disorder unit in Auckland.
The South Island's only specialist eating disorder unit - in the C Ward of Princess Margaret Hospital - has eight beds, two of which are allocated specifically to children and youth.
Other DHBs were were unable to confirm by deadline their number of beds or whether they sent patients to larger centres.
Several people whose families had been affected by eating disorders told the Herald on Sunday only those whose lives were in immediate danger because of their illness were accepted as inpatients in specialist units and that demand well exceeded the number of available beds.
A Christchurch woman whose daughter has battled anorexia nervosa for nearly two years said she and her husband struggled to get her adequate treatment, but considered themselves to be "lucky" because the girl, now aged 16, was eventually admitted to the C Ward at Princess Margaret Hospital.
The mother, who asked to remain anonymous to protect her daughter's privacy, said it appeared the treatment system for people battling eating disorders was broken.
"It is an ambulance waiting at the bottom of the cliff."
Medical staff did the best they could to help with the resources they had but some, particularly GPs, lacked specialist knowledge and most treatment programmes seemed to be underfunded, she said.
She told the Herald on Sunday she believed her daughter had been suffering from an eating disorder for at least two years when she was diagnosed in September 2015, but she and her husband didn't pick it because they didn't know a lot about the symptoms of eating disorders at the time.
After the diagnosis their family GP told them their daughter, who was aged 15, should try treatment in the form of an online programme.
It was only when the girl's weight plummeted to 35kg, her heart rate became dangerously low and her organs started to shut down that she was accepted as an inpatient.
She was in and out of the specialist unit for nine months as each time she reached a healthy weight she was discharged so that a bed could be freed up by another critically ill eating disorder patient.
The mother said more funding was needed for both community-based and inpatient treatment programmes so that doctors, nurses and parents were able recognise the symptoms of eating disorders more quickly and treatment could begin soon after the illness' onset.
Others spoken to by the Herald on Sunday, including Nicki Wilson, chairwoman for the Eating Disorders Association of New Zealand (EDANZ) which supports families and friends of sufferers, shared the woman's concerns.
The Green Party is supporting these calls for more funding to be allocated to the prevention, detection and treatment of eating disorders.
Greens' health spokeswoman Julie Anne Genter said as well as starting an inquiry into all mental health care, the party would increase funding for the treatment of eating disorders to match an increase in population and demand.
When asked by the Herald on Sunday whether the treatment options for eating disorder patients were meeting demand Health Minister Jonathan Coleman said ensuring Kiwis were able to access mental health services was a priority for the Government.
Coleman said Budget 2017 invested an extra $224 million into mental health services to help cope with the increasing demand. However, he did not confirm whether any of this would be allocated specifically to treating eating disorders.