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

Abstract

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 < 0.001) and 24-hour urine osmolality (n = 34, p = 0.003) decreased during daytime fasting but remained largely within the physiological range and returned to pre-fasting levels during night hours. BMI (body mass index), total body fat mass, and resting metabolic rate decreased during fasting (n = 34, p < 0.001), while body cell mass and body water appeared unchanged. The circadian phase estimated by transcript biomarkers of blood monocytes advanced by 1.1 h (n = 16, p < 0.005) during fasting and returned to pre-fasting values 3 weeks after fasting. Most observed changes were not detectable anymore 3 months after fasting. 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.

Keywords: chronobiology; diurnal fasting; fasting; hydration; intermittent fasting; religious; time-restricted eating; water deprivation.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2021 Koppold-Liebscher, Klatte, Demmrich, Schwarz, Kandil, Steckhan, Ring, Kessler, Jeitler, Koller, Ananthasubramaniam, Eisenmann, Mähler, Boschmann, Kramer and Michalsen.

Figures

Figure 1

A flow chart of visits with participant numbers.

Figure 2

Changes in parameters of hydration, i.e., plasma osmolality (A) and urine osmolality in 24-h, 12-h from 6 a.m.−6 p.m. and 12-h from 6 p.m.−6 a.m. samples (B). Changes relative to V0-values. Line graphs and error bars represent means and 95%-confidence intervals accordingly.

Figure 3

Changes in metabolic parameters over the study period (A: BMI, B: body fat mass, C: resting metabolic rate, D: glucose, and E: HbA1c). Changes relative to V0-values. Line graphs and error bars represent means and 95%-confidence intervals accordingly.

Figure 4

Bahá'í fasting advanced the circadian phase in particular of late chronotypes. (A) The circadian phase of 16 study participants was assessed, using the blood monocyte-based BodyTime assay (26) before (V0), during (V1), and 3 weeks after BF (V2). The circadian phase corresponds to the BodyTime-predicted DLMO, which usually occurs about 2 hours before habitual bedtime. (B) The extent of advancing the circadian phase during BF correlated with chronotype (i.e., the circadian phase before BF).