EMBODIED CHEMOSENSORY PERCEPTION: IMPACT OF METABOLIC STATE ON OLFACTORY AND GUSTATORY PERCEPTION IN HEALTHY HUMANS

Olfaction and taste are not only sensitive to external cues but also modulated by internal metabolic processes: Receptors for nutrients, neuropeptides, and (an)orexigenic hormones (e.g., insulin, orexin) are present in peripheral and brain regions of the olfactory and gustatory systems, enabling chemosenses to also function as sensors of peripheral and hypothalamic signals. To examine the effects of metabolic state on olfaction and gustation in humans, we manipulated nutritional status and macronutrient content while measuring olfactory and gustatory performance, and metabolic parameters. After 12-hour overnight fasting, 162 young healthy subjects (81 males, 81 females; BMI 18.8-30 kg/m²) were randomly assigned to either remain fasted or consume an equicaloric ~615 kcal carbohydrate-rich or fat-rich meal (satiated). We repeatedly measured capillary blood glucose, salivary insulin, and hunger. Olfactory performance (threshold = sensitivity; suprathreshold = discrimination, identification) and taste recognition were assessed using the Sniffin´ Sticks and Taste-Strips tests, respectively. Nutritional status manipulation was confirmed via blood glucose and salivary insulin. Olfactory sensitivity (threshold) was better when fasted than after fat-rich intake in participants with normal weight, while those with overweight showed an inverse pattern. Suprathreshold performance, involving higher-order cognitive processing, tended to be better in the carbohydrate-rich than fasted condition. Taste recognition (salty, bitter) was also influenced by the manipulation. Regression analyses revealed that blood glucose and insulin predicted olfactory performance differentially in fasted, carbohydrate-rich, and fat-rich conditions. The metabolism-to-olfaction pathway in humans is not only sensitive to fasting versus satiation, but differentially modulated by macronutrient content, sex, and BMI. (DFG-funded, GRK 274877981).