Sense of Smell and Its Role in Abnormal Eating Behavior

Olfaction and ghrelin may moderate emotional eating.

Reprinted from Eating Disorders Review
January/February Volume 27, Number 1
©2016 IAEDP

It seemed a fairly straightforward research project: analyzing the effect of olfactory capacity upon abnormal eating behavior. However, after a thorough literature review, Dr. Mohammed A. Islam, of the Hospital of Bellvitage-IDIBELL, Barcelona, and colleagues at other institutions in Spain and the United Kingdom found the answers were not so clear-cut (Front Psychol. 2015. Doi:10.3389/psyg.2015.01431). 

Olfactory capacity has been widely studied in a number of psychiatric disorders, including schizophrenia, depression, and dementia. Researchers have learned that the brain’s reward system is actively involved in eating behavior and reactions to olfactory stimuli. The few studies that have investigated a connection between olfactory capacity and eating disorders have reached conflicting conclusions, perhaps due to lack of sample size and available assessment procedures.

Dr. Islam and colleagues identified 1352 studies of olfaction and disordered eating after searching all electronic databases, including Medline, PubMed, and PsycINFO. Most research centered on patients with anorexia nervosa (AN). After all study criteria were met, only 14 studies remained in the evaluation. 

Results of individual studies varied so widely that the authors could not draw firm conclusions. For example, several studies suggested that patients with AN had a poorer sense of smell; however, a recent study (described later in this article), reached a different conclusion. An analysis of 5 studies of patients with BN, the authors found no differences between patients and the general population. 

A second study of taste and olfactory function

A second recent study from the same institution led by one of the co-authors of the review, evaluated smell and taste dysfunction among females with AN and a group of obese females (Endocrine. 2015 July [Epub ahead of print]). The goal was to explore the interactions between smell/taste capacity, gastric hormones, eating behavior, and BMI. The study group included 239 females, with 64 AN patients and 80 age-matched healthy controls, and 59 obese women and 36 healthy weight, age-matched controls.

Dr. F. Fernández-Aranda and co-workers used the Eating Disorders Inventory-2, the Symptom Checklist 90-revised, and the Dutch Eating Behavior Questionnaire, and also analyzed samples of peptides (ghrelin, peptide YY, and cholecystokinin) taken from the gastrointestinal tract of each participant. The sense of smell was assessed using “Sniffin’ Sticks,” which measure threshold, discrimination, and identification of smells.

Obese subjects and those with AN had distinctly different olfactory profiles and circulating ghrelin levels compared to controls. The researchers found that olfaction was clearly impaired in the obese participants but was increased in those with AN. Taste capacity did not vary between the study groups. Ghrelin levels were significantly decreased in obese subjects and were related to impairment of smell. These results may help to clarify this confusing literature, as they provide data using a well-validated methodology in an adequately sized sample.