New research done by the University of Otago, that studied the DNA of 17,000 people, suggests the origins of anorexia are both metabolic and psychiatric.
Clinical psychologist Jenny Jordan told TVNZ1's Breakfast what they discovered about the eating disorder.
"We’ve always known there’s been a heritability to anorexia and eating disorders. There's somewhere between 50 to 60 per cent risk of having the disorder if you’ve got a family member with it, but we didn’t really know what was heritable."
"We don’t have a good grip on the biology of anorexia, we are good at describing it, but the underlying biology is a bit of a mystery.
"This research is a really important first step in uncovering the biology," Ms Jordan says.
She says people that have anorexia matabolise fats differently.
"There is also a difference in their glycemic matabolism and hunger hormones.
"These things are not just in the acute stage of anorexia that you'd see a difference, this is actually in their genes from conception...it sets them up to respond differently."
There are currently no medications for anorexia.
"If we could find a biological treatment for anorexia that would be ground-breaking. That's a long way off at this stage, it needs the basic science in order to get to those next steps."