Experts warn that online "thin-spiration" blogs are encouraging life-threatening behaviour among slimmers, with girls as young as six being treated for severe eating disorders.
The director of New Zealand Eating Disorder Specialists, Charles Fishman, is alarmed at the popularity of websites touting potentially harmful tips for losing weight and displaying images of dangerously thin bodies.
"This gives them an outside source of confirmation that this is the right thing to do, thus adding to the danger," he said.
The warning is highlighted by a growing number of people being treated for eating disorders.
Numbers from the Ministry of Health show a steady, yearly rise in patients treated since 2008. The Waikato District Health Board recorded 44 patients treated in the same time frame.
Of those, 38 were female, 32 suffered from anorexia nervosa and all were aged 18 or under. More than half were aged 15-17 but there were patients as young as 6 or 7 being treated.
That is the "target audience" of these sites, said Mr Fishman. "They're certainly the most vulnerable. [These sites] normalise and even encourage behaviour that is life threatening.
Some sites promote using appetite suppressants, laxatives, cigarettes and drugs to help lose weight and feature images of stick-thin women, with protruding hip and collar bones being the crowd ‘favourite'."
Most of the blogs promote healthy eating and exercise but some take on a more sinister theme, encouraging starvation and promoting self harm as "punishment" for overeating - or eating at all.
They are laden with messages such as, "Thou shall not eat without feeling guilty", "I'm not yet a winner, I could be thinner, so I must go throw up dinner", and "being thin is more important than being healthy".
One popular blogging platform, Tumblr, was forced to review its policies around "Thinspo"-like blogs and will now take down sites "crossing the line" of promoting any type of self-harm, eating disorders or suicide.
However, Sean Lyons of NetSafe said with tens of millions of sites on Tumblr alone, even if one comes down there will be others.
"It's a case of how much easier it is to find and create these sites. With blogging platforms like Tumblr, anyone with an email address and the ability to click an upload button can do it," he said.
"Maybe we didn't see this years ago and sat in blissful ignorance but the internet provides a look into parts of society that we didn't know about before."
Mr Lyons also said taking the sites down impinges on basic freedom of speech, and is not the solution anyway.
"We need to reach out to the people that are going through this and provide support, rather than take it all down and think that's a solution," he said.
However, Dr Cate Curtis, a psychology lecturer at Waikato University, said "thin-spiration" sites could have a detrimental effect on those struggling with self esteem or body image, particularly around summer.
"The thing is, in winter if you're not feeling terribly confident about your figure it's relatively easier to hide that than in summer. Women in general already have very high rates of body dissatisfaction which at the extreme end can lead to eating disorders, but can also result in day to day unhappiness," she said.
"Put your health first and foremost and be healthy."
- Waikato Times