Objective: Smell plays an important role in feeding behavior. We therefore tested whether insulin as a postprandial signal is involved in the regulation of olfactory function.
Research design and methods: We assessed olfactory thresholds in eight lean subjects (age: 34 ± 7 years, M/F: 5/3) before and during a 2-h hyperinsulinemic (1 mU kg(-1) min(-1)) euglycemic clamp and in eight lean fasted subjects (age: 36 ± 6 years, M/F: 5/3) without insulin infusion at the same time of the day. To define odor thresholds, standardized 'sniffing sticks' were used.
Results: Odor thresholds decreased from 7.8 ± 1.2 to 6.2 ± 1.1 during euglycemic hyperinsulinemia (P=0.0173), representing an increase in odor threshold. In the control group, odor thresholds were 8.3 ± 1.6 and did not change after 120 min of fasting (8.9 ± 2.2, P=0.6).
Conclusions: Increased insulin levels lead to a reduced smelling capacity, potentially reducing the pleasantness of eating. Therefore, insulin action in the olfactory bulb may be involved in the process of satiation and may thus be of interest in the pathogenesis of obesity.