As Insulin Rises, Sense of Smell Decreases Potentially Affecting Desire to Eat

In a paper in the International Journal of Obesity, Dr. Andreas Fritsche and colleagues report on new efforts to understand the mechanisms underlying excess food intake and the regulation of feeding behavior. The researchers from the University of Tubingen, Germany, say there is evidence that hunger and satiety influence olfactory thresholds. Sensitivity appears to be higher before than after eating, but study results differ. 

To investigate further, the team used standardized 'sniffing sticks' to evaluate odor thresholds in 14 lean healthy subjects with a mean age of about 35 years. All fasted for at least 10 hours before testing.

Eight subjects were evaluated before and during a two-hour hyperinsulinemic-euglycemic clamp. Testing was also carried out at the same time of day without insulin infusion in eight subjects (including two who had been tested with the clamp as well).

In the control group, odor thresholds did not change over 2 hours. In the clamp group, however, they fell significantly from baseline.

"Clearly," say the investigators, "the modulation of olfaction by insulin in healthy subjects is only part of the complexity of feeding behavior."

But, they add, "Elevated insulin levels as physiologically seen after food intake do influence olfactory function."

The investigators conclude that reduced smelling capacity could diminish the pleasure of eating - which means that "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."

Int J Obesity. Posted online November 23, 2010