Circadian Regulation of Taste Sensitivity in Human and Rat Active Periods

Most organisms exhibit endogenous 24-h rhythms that align physiology and behavior with the time of day; however, whether taste sensitivity oscillates in a circadian manner remains unclear, limiting our understanding of its role in feeding behavior. Here, we show that sensitivity to sweet and bitter tastes exhibits circadian modulation, peaking during the active period: daytime in humans and the dark phase in nocturnal rats. In humans, the rhythmicity of sweet taste was evident in detection but not recognition thresholds, indicating circadian modulation at the level of primary sensory processing rather than higher-order cognitive processes. In rats, increased sensitivity during the dark phase was accompanied by upregulation of taste-related genes in type II taste cells in tongue. These findings provide evidences that circadian regulation of taste sensitivity is conserved across species and appears to operate predominantly at the peripheral level. This mechanism may have evolved to optimize energy intake while minimizing exposure to dietary toxins, potentially contributing to survival and continuing to influence modern eating behavior through circadian-sensory-nutritional interactions.