Abstract
Humans show individual differences of biological rhythm phase, and can be classified into the “morning type” (peak performance being achieved in the early part of the day) or the “evening type” (peak performance towards the end of the day) . We therefore hypothesized that evening-type individuals would show different daytime variations of autonomic nervous activity, gastric motility and appetite sensations, which are under the control of the biological clock. In this study, 34 young women began fasting at 22:00 h on the previous night and ate test meals at a pre-determined time on the test day. Electrogastrography, electrocardiography (cardiac autonomic nerve activity) , appetite sensations, sleepiness, and core (eardrum) temperature were measured from 8:00 to 20:00 h at 1-hour intervals. After completion of all measurements, the subjects completed a morningness-eveningness questionnaire, and were divided into morning- or evening-preference types. Evening-preference individuals demonstrated a higher heart rate, a predominance of sympathetic nerve activity and greater sleepiness in the daytime. Moreover, they had a significantly lower hunger score during the morning, and did not show a significant shift in the frequency of postprandial gastric motility as compared with morning-preference individuals. Our results suggest that an evening-preference lifestyle may be associated with attenuation of appetite and vitality during the morning.
