Effects of Daytime Dry Fasting on Hydration, Glucose Metabolism and Circadian Phase : A Prospective Exploratory Cohort Study in Bahá'í Volunteers

Background: Religiously motivated Bahá'í fasting (BF) is a form of intermittent dry fasting celebrated by abstaining from food and drinks during daylight hours every year in March for 19 consecutive days.Aim: To test the safety and effects of BF on hydration, metabolism, and the circadian clock.Methods: Thirty-four healthy Bahá'í volunteers (15 women) participated in this prospective, exploratory cohort study. Laboratory examinations were carried out in four study visits: before fasting (V0), in the third week of fasting (V1) as well as 3 weeks (V3) and 3 months (V4) after fasting. Data collection included blood and urine samples, anthropometric measurements and bioelectrical impedance analysis. At V0 and V1, 24- and 12-hour urine and serum osmolality were measured. At V0-V2, alterations in the circadian clock phase were monitored in 16 participants. Our study was augmented by an additional survey with 144 healthy Bahá'í volunteers filling out questionnaires and with subgroups attending metabolic measurements (n = 11) and qualitative interviews (n = 13), the results of which will be published separately.Results: Exploratory data analysis revealed that serum osmolality (n = 34, p Conclusions: Results indicate that BF (Bahá'í fasting) is safe, has no negative effects on hydration, can improve fat metabolism and can cause transient phase shifts of circadian rhythms.Trial Registration:https://www.clinicaltrials.gov/, identifier: NCT03443739.publishe