An international study involving more than 500 New Zealand participants has uncovered distinct genetic signatures for binge eating and anorexia nervosa, reshaping how eating disorders are understood.

The research provides some of the clearest evidence yet that eating disorders are influenced by both psychiatric and metabolic biology, rather than being solely psychological illnesses.

Led by researchers at King’s College London and the University of North Carolina, the study is the first to map and directly compare the genetic profiles of binge-eating behaviour and anorexia nervosa on a large scale.

Genetic data from more than 500 New Zealand participants was contributed by a University of Otago Faculty of Medicine, Christchurch research team.

The researchers analysed DNA from tens of thousands of people worldwide, finding that although binge eating and anorexia nervosa shared some genetic influences, the conditions also differed in significant ways.

Associate Professor Jenny Jordan, a clinical psychologist in the University of Otago’s Department of Psychological Medicine, said the findings challenged the idea that eating disorders could be understood solely through a psychological lens.

“Even though these two conditions both fall under the category of eating disorders, they clearly differ deeply on a biological level,” Jordan said.

Professor Martin Kennedy, from the university’s Department of Pathology and Molecular Medicine, said the research provided some of the strongest evidence yet that both psychiatric and metabolic biology contributed to eating disorders.

“By analysing DNA from tens of thousands of people worldwide with binge eating or anorexia nervosa, we can start to see clear genetic signatures for each condition,” Kennedy said.

For the first time, researchers identified six regions of the genome associated with binge-eating behaviour, including one close to FTO, a gene known for its relationship with body weight.

The researchers studied binge eating as a behaviour that can occur across several eating disorders, rather than focusing solely on people diagnosed with binge-eating disorder.

Eight genomic regions were associated with anorexia nervosa.

Both conditions also had genetic connections with other psychiatric disorders, including depression and anxiety, but the patterns differed.

Anorexia nervosa displayed a stronger genetic relationship with obsessive-compulsive disorder, while binge eating was more strongly associated with attention deficit hyperactivity disorder.

Genetic factors associated with higher body weight were also linked to an increased likelihood of binge eating.

For anorexia nervosa, the relationship went in the opposite direction, with genetic factors associated with higher body weight appearing to reduce the likelihood of developing the disorder.

However, the researchers found the genetic contribution to eating disorders could not simply be explained by genes influencing body weight or body mass index.

The findings instead supported the concept of eating disorders as “metabo-psychiatric” conditions, shaped by an interplay of metabolic and psychiatric genetic factors.

Jordan said the discovery could eventually lead to treatments better tailored to the biology of individual conditions.

“These results not only help us understand both shared and distinct causes of these eating-related traits but may also help us develop more precise treatments targeting the specific biology of each condition,” she said.

Eating disorders could affect people across a wide range of body sizes and have serious physical and psychological consequences.

Kennedy said New Zealand participants were helping build the evidence needed for the next generation of eating-disorder research.

“This research is fleshing out the genetic and biological underpinnings of eating disorders and will create new opportunities for improved treatment and ideally prevention,” he said.

“We are excited that so many New Zealand participants have agreed to contribute to these important international studies.”

The next phase will draw on about 4000 New Zealanders who have contributed to the Eating Disorder Genetics Initiative, further strengthening the country’s role in international research.

The research was published in Nature Mental Health.