Eating disorders have the highest mortality rate of any psychiatric disorder. Now mental health researchers in Denmark have found evidence that people with anorexia nervosa have an enhanced sense of smell. The findings, published in the open-access journal PLOS One, could lead to a new avenue of treatment for the potentially deadly illness.

Anorexia is characterized by body image distortion and extremely low body weight. The new research suggests that olfactory sensitivity — meaning a heightened sense of smell — plays a role in the disorder.

“The interest in olfaction and anorexia nervosa began with the intention to understand why it is so difficult to recover from this disorder in some, but not all, cases. My colleagues and I decided to study social functioning in persons with anorexia nervosa, along with areas that might relate to social functioning,” explained the study’s corresponding author, Mette Bentz of the Mental Health Services in the Capital Region of Denmark and the University of Copenhagen.

“The sense of smell is associated with social functioning in other psychiatric disorders, and therefore, olfaction might be a simpler way to measure individual differences in persons with anorexia nervosa, which might predict functioning in social domains.”

“Further, the sense of smell plays a role in eating for healthy persons, and a core feature of anorexia nervosa is disordered eating. Therefore, altered olfaction might be involved in the core symptoms of anorexia nervosa as well,” Bentz told PsyPost.

“We knew from the research of others that olfaction shares some brain networks with executive functions, such as mental flexibility. Mental flexibility is in turn reduced in adults with anorexia nervosa and might explain why it is so difficult to change cognitive and behavioral patterns of anorexia nervosa, once they are firmly in place. However, young persons with a short duration of the disorder are yet understudied, and therefore we set out to focus on this specific group.”

The study was based on 43 females with first-episode anorexia nervosa, 28 females who had recovered from anorexia nervosa , and 41 female participants with no history of anorexia nervosa. The participants were between 14 and 22 years old.

The researchers found that participants with first-episode anorexia nervosa tended to have a better sense of smell.

“Young persons with anorexia nervosa have a heightened olfactory sensitivity, in other words they tend to perceive lighter odors, which the average control persons cannot detect,” Bentz explained. “The same is true for young persons who are fully recovered from anorexia nervosa. However, when asked to identify the odor, only those, who were presently ill, performed better, and only if they were not depressed.”

“The superior olfaction in those who had anorexia nervosa or were recovered from anorexia nervosa was not related to their cognitive or social functioning,” she added.

“The superior olfaction may be related to anxiety in general concerning bodily senses, or anxiety specifically concerning food related stimuli, and therefore we speculate that superior olfaction might be involved in exacerbating disordered eating in anorexia nervosa.”

The study, like all research, has some limitations.

“First, only females participated in this study, so the results only pertain to females,” Bentz told PsyPost.

“Second, it is difficult to test odor sensitivity in a reliable fashion for several reasons; for instance, the solution used to test sensitivity in our study stimulates not only the olfactory receptors, but other receptors in the nose as well.”

“Third, in order to understand whether the sense of smell is altered before anorexia nervosa, and how it may change during the cause of illness and recovery, one would need to assess the same individuals several times at different time points, rather than comparing different groups of individuals, as we did in the present study.”

But if the research pans out, it could lead to new treatments that help restore a healthy weight and eating habits in those with anorexia nervosa.

“The process of renourishment is extremely stressful for individuals with anorexia nervosa, as they need to confront and overcome their fear of eating on a daily basis,” Bentz told PsyPost. “If avoiding strong smells can make this process a bit less stressful, it is definitely worth trying. Also, a gradual habituation to odors might support the overcoming of fear of eating. However, treatment modifications should always be tested before wider implementation, and this study may serve as part of the groundwork for such a testing in the future.”

The study, “Heightened Olfactory Sensitivity in Young Females with Recent-Onset Anorexia Nervosa and Recovered Individuals“, was also co-authored by Johanne Guldberg, Signe Vangkilde, Tine Pedersen, Kerstin Jessica Plessen, Jens Richardt Moellegaard Jepsen.