[Impacts of mastication frequency on circadian rhythm of glucose metabolism].

Postprandial glucose concentration is dependent on the time of day and its concentration in the morning is lower than in the evening. The circadian rhythm of glucose metabolism is regulated by the central circadian pacemaker in the suprachiasmatic nucleus (SCN). Both the SCN circadian clock and the pancreatic clock play important role in generating and maintaining the circadian rhythm of glucose metabolism. Also, short sleep duration and circadian misalignment are closely associated with a decrease in insulin sensitivity and an increase in type2 diabetes. Increased frequency of mastication and/or thorough chewing has been reported to alter the secretion of hormones related to appetite and energy metabolism. Furthermore, we have reported that the effect of mastication on postprandial glucose metabolism is dependent on the time of day and frequency of mastication. Morning mastication but not evening decreases postprandial blood glucose concentrations and increases insulin secretion at 30 min and so-called the insulinogenic index as a marker of early-phase β-cell function. This novel finding may aid in reducing the incidence of obesity and type 2 diabetes mellitus. This review covers the basic concept of the mammalian human circadian system, the underlying mechanism causing phase adjustment of the circadian rhythms in the SCN and peripheral organs, and the effect of eating behavior (e.g., chewing frequency) on the circadian rhythm of glucose metabolism.