The influence of intermittent fasting on the circadian pattern of melatonin while controlling for caloric intake, energy expenditure, light exposure, and sleep schedules: A preliminary report

<br><b>Aims:</b> We hypothesized that if we control for food composition, caloric intake, light exposure, sleep schedule, and exercise, intermittent fasting would not influence the circadian pattern of melatonin. Therefore, we designed this study to assess the effect of intermittent fasting on the circadian pattern of melatonin.<br><b>Methods:</b> Eight healthy volunteers with a mean age of 26.6 ± 4.9 years and body mass index of 23.7 ± 3.5 kg/m² reported to the Sleep Disorders Center (the laboratory) on four occasions: (1) adaptation, (2) 4 weeks before <i>Ramadan</i> while performing Islamic intermittent fasting for 1 week (fasting outside <i>Ramadan</i> [FOR]), (3) 1 week before <i>Ramadan</i> (nonfasting baseline [BL]), and (4) during the 2^nd week of <i>Ramadan</i> while fasting (<i>Ramadan</i>). The plasma levels of melatonin were measured using enzyme-linked immunoassays at 22:00, 02:00, 04:00, 06:00, and 11:00 h. The light exposure, meal composition, energy expenditure, and sleep schedules remained the same while the participants stayed at the laboratory.<br><b>Results:</b> The melatonin levels followed the same circadian pattern during the three monitoring periods (BL, FOR, and <i>Ramadan</i>). The peak melatonin level was at 02:00 h and the trough level was at 11:00 h in all studied periods. Lower melatonin levels at 22:00 h were found during fasting compared to BL. Cosinor analysis revealed no significant changes in the acrophase of melatonin levels.<br><b>Conclusions:</b> In this preliminary report, under controlled conditions of light exposure, meal composition, energy expenditure, and sleep-wake schedules, intermittent fasting has no significant influence on the circadian pattern of melatonin.<br>