Anorexia and other eating disorders may be linked to a nervous system experiencing inflammation caused by stress,
according to an international review co-authored by a University of Auckland researcher.
Published in Frontiers in Psychology, the collaborative review from the Universities of Auckland, Turku (Finland), Daugavpils (Latvia) and Tartu (Estonia)
concludes that the variation in eating disorders between people may arise from individual differences in gut microbiota,
as well as their degree of response to stress, which in turn affects inflammation in the nervous system and the
regulation of the mood chemical serotonin in the brain.
Serotonin regulation in the brain originates in two mid-brain areas (the dorsal raphe and the median raphe) that control
neurotransmitters associated with a range of cognitive disorders like depression, bipolar disorder and schizophrenia.
The review of research by Dr Severi Luoto and colleagues has resulted in the team suggesting a new evolutionary
neurobiological model to understand eating disorders.
“The new model predicts that when there are changes in gut microbiota, stress levels and responsivity to stress, a
patient’s symptoms and eating disorder diagnosis will change,” says Dr Luoto.
“Similarly, the evidence we’ve reviewed suggests that the difference between whether people are more likely to suffer
bulimia nervosa (BN) or anorexia nervosa (AN) arises from the degree of neuroinflammation caused by chronic stress, with
AN patients suffering stronger neuroinflammation than BN patients.”
“Weight loss obsession is mediated by pervasive thoughts about food, body weight, diet, physical exercise and
appearance, as well as obsessive-compulsive disorder-like behaviour which tries to solve these issues.”
Based on the review, the authors suggest the stronger the neuroinflammation in anorexia patients, the stronger is their
obsession to lose weight and their fear of gaining weight, and the more persistent and extreme are their obsessive
behaviours.
Rather than thinking about eating disorders as separate conditions, the authors believe the disorders should be viewed
on a continuum. The new evolutionary neurobiological model answers four key questions: why symptoms and behaviours
overlap across a range of eating disorders; why diagnosing eating disorders is challenging; why patient diagnoses may
shift between different eating disorders over time; and why anorexia nervosa exists in two forms – fat-phobic and
non-fat-phobic.
To come to their conclusions, the authors reviewed findings from hundreds of scientific articles and several books
spanning multiple decades, with the earliest piece dating from 1950.
While converging (although indirect) evidence indicates that patients with anorexia nervosa have neuroinflammation, Dr
Luoto says PET (positron emission tomography scanning) studies are needed to provide more support for the hypothesis
that neuroinflammation is the biological mechanism that underlies the spectrum of eating disorders.
“Follow-up studies in which stress hormone levels, stress responsivity, serotonin levels, neuroinflammation and the
composition of gut microbiota are measured from patients in the course of eating disorder(s) would reveal whether
symptoms change according to predictions that arise from our study’s model," he says.
The authors also suggest that media literacy programmes and cognitive behavioural therapy based on evolutionary
psychiatry could further shift patients’ negative self-image and ideals of thin beauty in a healthier direction.
“Ultimately, we hope the new model will promote further empirical work, provide substantial improvements in therapeutic
treatments and drugs for eating disorders and eventually be of practical use to the millions of people all over the
world who lead lives that are severely debilitated by these pervasive disorders,” says Dr Luoto.
Eating Disorders: An Evolutionary Psychoneuroimmunological Approach was written by Markus J. Rantala (University of Turku, Finland), Severi Luoto (University of Auckland), Tatjana Krama
(Daugavpils University, Latvia) and Indrikis Krams (University of Tartu, Estonia).