Systematic review of olfactory shifts related to obesity

Abstract

Objective: The modern food environment is a key driver of rising levels of obesity.While olfaction is known to play a major role in food choice; however, its relationship to obesity is yet to be understood. This review assesses current knowledge of the interaction between obesity and olfaction.Methods: This review is based on observational studies comparing olfactory abilities across weight groups (N = 10) and clinical studies evaluating olfactory changes following bariatric surgery (N = 9). Meta-analyses were performed on data collected by a standard olfactory assessment tool (Sniffin΄ Sticks), to test whether olfaction has any association with body weight or bariatric surgery.Results: This review synthesizes findings derived from 38 datasets, with a total of 1432 individual olfactory assessments. The meta-analyses suggest that olfactory function is negatively correlated with body weight. In addition, Roux-en-Y gastric bypass patients frequently report olfactory changes, yet more pronounced and immediate shifts have been observed among sleeve gastrectomy recipients.Conclusions: Our review finds strong evidence for the link between olfaction and obesity and indicates that bariatric surgery (particularly the sleeve gastrectomy) is effective in reversing olfactory decline associated with obesity. In conclusion, we present mechanistic models to underpin the observed relationship between olfaction and obesity.

Body-Mass-Index Associated Differences in Ortho- and Retronasal Olfactory Function and the Individual Significance of Olfaction in Health and Disease

“…Research progress in this field derives mostly from experimental studies in rodents [7,10,30] and there is a clear need for clinical investigations in humans-especially since olfactory testing methods (e.g., retronasal tests) have become more standardized and hence comparable [17,21,31]. Notably, the number of publications on bodyweight and multiple olfactory dimensions is still low and information on the relation of retronasal olfactory tests and BMI is still missing [9].…”

“…Food choice is strongly affected by chemosensory perceptive abilities. Broad research efforts have been put into the relations between taste function and bodyweight [9], but evidently, flavor perception may influence food liking (and hence food choice) more markedly. Liking and reward value seem to be dependent on whether the food has been eaten recently or not [42] and if flavors have been encountered before.…”

“…Previous investigations showed olfactory abilities to decrease in mice models with weight gain based on fatty nutrition, but this was not reversible when losing weight afterwards [10]. In contrast, bariatric surgeries in humans (in particular sleeve gastrectomy) seem to increase olfactory function [9]. Yet, to our knowledge, studies are missing which investigate whether a non-surgical reduction in bodyweight in humans affects olfactory capacities.…”

“…Presumable in consequence, olfactory dysfunctions can result in changes in dietary behavior [8]. At the same time, bodyweight negatively correlates with orthonasal olfactory abilities, while studies on retronasal odor perception (i.e., flavor) are still lacking [9]. Whether reduced olfactory abilities are co-causative for obesity or obesity causes an olfactory decline in humans is debatable.…”

Olfactory Memory in Depression: State and Trait Differences between Bipolar and Unipolar Disorders

“…Olfactory impairment seen in obesity can be related to various metabolic and endocrine defects, such as hyperleptinemia, hyperglycemia, and insulin resistance. However, weight loss through bariatric surgery may reverse the olfactory decline [21].…”