Film director Miryam Jacobi said eating disorders were an aspect of mental health that wasn't talked about enough.
"People think that it's just a diet gone too far or someone who just needs to snap out of it," Jacobi said.
She said there were many different forms of eating disorders that often went undiagnosed.
"Orthoexia, which is over-exercising, is becoming really common, particularly in guys it can so easily go undiagnosed.
"Some of the people in the documentary who struggled with bulimia, their condition went on for many years because no one knows about the signs and how to talk about it," Jacobi said.
Claudia, who battled anorexia nervosa, said the one therapist was able to make a difference in her life because she treated her like a person.
"Every other doctor treated me like anorexia. They didn't talk to me, they talked to my parents or to anorexia and it wasn't about how I felt."
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.
In 2016, 1290 New Zealanders with severe eating disorders were treated through these services.
But Jacobi said it was hard to put a figure on just how many people were struggling with an eating disorder in New Zealand because of how difficult it was to detect.
"It's really important that eating disorders are talked about because the thing with eating disorders is people suffering thrive of secrecy - the longer it's a secret, the longer it can have power over you."
Jacobi said every person she spoke to while making the documentary all had a moment when they talked to someone and things changed.
"Lucy in the documentary said she when she first told her aunty she was so surprised by her reaction ... her aunty told her that it was 'okay not to be okay' and that was a massive revelation for her.
"The biggest step of all is asking for help, so this documentary is really about getting people to talk."
Disorder is part of the Someday Stories funded by New Zealand On Air and will launch online on August 27.
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