Anorexia may be fuelled by a desire to get thin, more than by a fear of getting fat, scientists have claimed. Patients may even find pleasure in losing weight, a phenomenon that may be influenced by their genes.
The serious eating disorder is characterised by three clinical criteria in the DSM-5, the international reference for the definition of mental health disorders. These criteria are a restriction of food intake leading to an abnormally low body weight, a distorted perception of body weight and an intense fear of gaining weight. Most patients are women although men can also be affected.
There are limited therapeutic options and no pharmacological treatment available.
This is why the latest study, published in Translational Psychiatry, investigates whether anorexia could be better defined clinically, to help physicians come up with new ways of caring for anorexia sufferers.
The scientists indeed believed that "a fear of gaining weight" - which suggests anorexia is a form of anxiety disorder - is not really accurate.
"Treatments that are usually given to patients with phobia or anxiety are not effective for anorexia nervosa. Although patients do tell us that they fear getting fat, we believe this is a mirrored reaction to the fact they have pleasure in getting thin", lead author Philip Gorwood, from Hopital Sainte Anne in Paris, told IBTimes UK.
"In our study, we hypothesise that patients feel pleasure at becoming thin, rather than fear of becoming fat. The disorder may be more closely associated to a form of addiction rather than to an anxiety, with completely different neurological implications".
Using sweat to tell patients' motivation
The problem with anorexia is that doctors may focus too much on patients' discourse, and do not look at whether they might have motivations for not eating other than what they tell them. In this research, the scientists wanted to get more objective information about the patients' disorder.
They submitted 70 patients to a skin conductance test, during which their sweating rate was measured as they were exposed to various images of underweight, normal and overweight silhouettes. The patients themselves were of varying weights, as some were in remission with a normal weight, while others were still underweight, which allowed researchers to look for mechanisms to the disorders which were independent from the actual state the patients were in.
The emotion caused by some of the images led to a rapid and automatic increase in skin conductance and sweating. This was the case when anorexic subjects looked at underweight people, with an increase of skin conductance associated to positive emotions.
Their response was compared to that of healthy subjects, who showed no particular responses having viewed images of underweight individuals.
"A higher positive value of starvation – rather than more negative one of overweight – might more accurately define females with anorexia", the researchers say.
A genetic influence
Scientists also point out that anorexia is a highly heritable disorder, with a specific form (or allele) of the brain-derived neurotrophic factor, or BDNF, gene – a gene involved in neuroplasticity – often present in anorexic patients.
In this study, the researchers found that the presence of this allele was positively correlated to the increase in skin conductance when people looked at images of underweight individuals.
This allele may thus influence anorexic people to feel positive emotions and pleasure at the prospect of losing weight.
These findings may be an important step towards a better understanding of what anorexia is and how to better address patients's concerns and issues. They could also lead to the development of new treatments based on what we know so far of addictive disorders.