METHODS • REVIEW Effect of diurnal fasting on sleep during Ramadan: a systematic review and meta-analysis Mo’ez Al-Islam E. Faris 1 & Haitham A. Jahrami 2,3 & Fatema A. Alhayki 3 & Noor A. Alkhawaja 3 & Ameera M. Ali 3 & Shaima H. Aljeeb 3 & Israa H. Abdulghani 3 & Ahmed S. BaHammam 4,5 Received: 15 August 2019 /Revised: 19 November 2019 /Accepted: 25 November 2019 # Springer Nature Switzerland AG 2019 Abstract Purpose The current meta-analysis aimed to obtain a more stable estimate of the effect size of Ramadan diurnal intermittent fasting (RDF) on sleep duration and daytime sleepiness. Methods Databases (Scopus, ScienceDirect, ProQuest Medical, PubMed/MEDLINE, Web of Science, EBSCOhost, Cochrane, CINAHL, and Google Scholar) were searched from database inception to the end of June 2019. The sleep quality measures analyzed were excessive daytime sleepiness (EDS) measured by the Epworth sleepiness scale (ESS) and total sleep time (TST). Subgroup analyses for age, sex, and levels of physical activity were conducted. Results We identified 24 studies (involving 646 participants, median age 23.7 years, 73% men) conducted in 12 countries from 2001 to 2019. The results revealed that TST decreased from 7.2 h per night [95% confidence interval (CI) 6.7–7.8] before Ramadan to 6.4 h (95% CI 5.3–7.5) during Ramadan, while the ESS score increased slightly from 6.1 (95% CI 4.5–7.7) before Ramadan to 7.0 (95% CI 5.2–8.8) during Ramadan. Effect sizes on sleep quality measures during RDF demonstrated a moderate reduction in TST (number of studies, K = 22; number of subjects, N = 571, Hedges’ g value of -0.43, 95% CI - 0.64 to -0.22, Q = 90, τ 2 = 0.15, I 2 = 78%, P < 0.001), while ESS score showed negligible effect on EDS (K = 9, N = 362, Hedges’ g value of -0.06, 95% CI -0.43 to 0.28, Q = 21, τ 2 = 0.13, I 2 = 76%, P value = 0.001). Conclusion During the month of Ramadan, there is approximately a 1 hour reduction in TST and nearly a 1 point increase in the ESS score. Keywords Caloric restriction . Epworth sleepiness scale (ESS) . Excessive daytime sleepiness (EDS) . Diurnal intermittent fasting . Ramadan . Total sleep time (TST) Introduction Fasting is an ancient practice defined as voluntary abstinence from food and/or drinks [1], which has been recently adopted as a health and fitness trend [2]. Muslims fast from dawn to sunset for 29–30 days during Ramadan. Ramadan fasting for- bids eating foods, drinking water, sexual activities, and smoking during daytime [3] and affects daily lifestyle. The predawn meal is taken before dawn (suhoor), and the main course is taken after sunset (iftar)[4]. This shift in mealtime during Ramadan might be associated with changes in caloric and nutrient intakes (heavy meals), which are variable accord- ing to the variations in dietary and social behaviors practiced during the fasting month [5, 6]. Religious practices can affect sleep [7, 8], and during Ramadan, many events occur at night [7, 9]. Ramadan can occur during any four seasons of the Gregorian year [10]. Daytime fasting is therefore longer during summer and shorter * Ahmed S. BaHammam ashammam2@gmail.com; ashammam@ksu.edu.sa 1 Department of Clinical Nutrition and Dietetics, College of Health Sciences/Research Institute of Medical and Health Sciences (RIMHS), University of Sharjah, Sharjah, United Arab Emirates 2 Ministry of Health, Manama, Bahrain 3 College of Medicine and Medical Sciences, Arabian Gulf University, Manama, Bahrain 4 Department of Medicine, College of Medicine, University Sleep Disorders Center, King Saud University, Box 225503, Riyadh 11324, Saudi Arabia 5 The Strategic Technologies Program of the National Plan for Sciences and Technology and Innovation in the Kingdom of Saudi Arabia, Riyadh, Saudi Arabia Sleep and Breathing https://doi.org/10.1007/s11325-019-01986-1