The Role of the Olfactory System in Obesity and Metabolism in Humans: A Systematic Review and Meta-Analysis

Abstract

Obesity, linked to chronic diseases, poses a global health challenge. While the role of the olfactory system in energy homeostasis is well-documented in rodents, its role in metabolism regulation and obesity in humans remains understudied. This review examines the interplay between olfactory function and metabolic alterations in human obesity and the effects of bariatric surgery on olfactory capabilities in humans. Adhering to PRISMA guidelines, a systematic review and meta-analysis was conducted, focusing exclusively on original human studies. From 51 articles, 14 were selected for the meta-analysis. It was found that variations in olfactory receptor genes influence the susceptibility to odors and predisposition to weight gain and poor eating habits. Bariatric surgery, particularly sleeve gastrectomy, shows significant improvements in olfactory function (SMD 2.37, 95% CI [0.96, 3.77], I = 92%, p = 0.001), especially regarding the olfactory threshold (SMD −1.65, 95% CI [−3.03, −0.27], I = 81%, p = 0.02). There is a bidirectional relationship between olfactory function and metabolism in humans. Bariatric surgery improves olfactory perception in obese patients, but it is still unclear if impacting the olfactory system directly affects eating behavior and the energy balance. However, these findings open novel avenues for future studies addressing the olfactory system as a novel target to alter systemic metabolism in humans.

Role of Ectopic Olfactory Receptors in the Regulation of the Cardiovascular–Kidney–Metabolic Axis

“…Systemic metabolic disorders, including metabolic syndrome, obesity, and diabetes, act as initiating events in the pathogenesis of the cardiovascular-kidney-metabolic syndrome [10,11]. Single nucleotide polymorphisms in several dozens of OR genes have been linked to the increased occurrence of such metabolic disorders [149,150]. It is now well recognized that by altering the sense of smell, dysfunction of olfactory signaling in the nasal epithelium can directly predispose to poor eating habits and body weight gain [150].…”

“…Single nucleotide polymorphisms in several dozens of OR genes have been linked to the increased occurrence of such metabolic disorders [149,150]. It is now well recognized that by altering the sense of smell, dysfunction of olfactory signaling in the nasal epithelium can directly predispose to poor eating habits and body weight gain [150]. On the other hand, the role played by altered ectopic OR signaling in the impairment of systemic metabolic homeostasis is much less well appreciated.…”