Abstract
Olfactory perception determines food selection behavior depending on energy homeostasis and nutritional status. The mechanisms, however, by which metabolic signals in turn regulate olfactory perception remain largely unclear. Given the evidence for direct insulin action on olfactory neurons, we tested olfactory performance (olfactory threshold, olfactory discrimination) in 36 subjects of normal- and overweight after administration of three different insulin doses (40 I.U., 100 I.U., 160 I.U.) or corresponding placebo volume in a within-subject design. Poor peripheral insulin sensitivity as quantified by HOMA-IR in baseline condition and increases in systemic insulin levels reactive to intranasal administration predicted poor olfactory performance. In contrast, intranasal insulin enhanced odor perception with a dose-dependent improvement of olfactory threshold. These findings indicate a new diametric impact of insulin on olfactory perception depending on peripheral or central availability.
Highlights
The sense of smell impacts food selection behavior
Intranasal insulin applications are associated with reactive blood insulin changes[25] that might in turn interact with olfactory perception and mask the intranasal insulin effects
While there was no correlation with BMI, average performance of both olfactory threshold (r(31) = −0.455, p = 0.008) as well as odor discrimination (r(31) = −0.352, p = 0.04) were correlated with average homeostasis model assessment of insulin resistance (HOMA-IR) at baseline level
Summary
The sense of smell impacts food selection behavior. The olfactory system does help to identify the chemical composition of food and serves as an internal sensor for the nutritional status[1,2]. We hypothesized that correcting for reactive changes of blood insulin levels will reveal a dose-dependent modulation of olfactory perception by intranasal insulin with stronger effects of higher doses. We assessed the relation between olfactory threshold and the pre-experimental variable insulin sensitivity (quantified by HOMA-IR) and the reactive variable blood insulin change after intranasal insulin application.
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