SUMMARYExperimental fasting has been shown to alter the sleepwakefulness pattern in various species. As fasting during Ramadan is distinct from experimental fasting, the physiological and behavioural changes occurring during Ramadan fasting may differ from those occurring during experimental fasting. There has been increased interest in recent years in sleep changes and daytime sleepiness during Ramadan. Moreover, many of those who fast during Ramadan associate this fasting with increased daytime sleepiness and decreased performance. This raises the question of whether Ramadan fasting affects sleep. In this review, we discuss the findings of research conducted to assess changes in sleep pattern, chronobiology, circadian rhythms, daytime sleepiness and function and sleep architecture during the month of Ramadan. Where applicable, these findings are compared with those obtained during experimental fasting.

PurposeThis study aimed to assess the effect of diurnal intermittent fasting (DIF) during and outside of the month of Ramadan on plasma levels of interleukin (IL)-1β, IL-6, and IL-8, while controlling for sleep/wake pattern, sleep length and quality, meal composition, energy consumption and expenditure, and light exposure. DIF outside of the month of Ramadan was performed to evaluate the effect of DIF in the absence of the way of life accompanying Ramadan.MethodsTwelve healthy male volunteers with a mean age of 25.1 ± 2.5 years arrived to the sleep laboratory on 4 times: 1) adaptation, 5 weeks before Ramadan; 2) 4 weeks before Ramadan while performing DIF for 1 week (fasting outside of Ramadan; FOR); 3) 1 week before Ramadan (non-fasting baseline; non-fasting BL); and 4) After completing 2 weeks of Ramadan while performing DIF. Plasma levels of cytokines were assessed using enzyme-linked immunoassays at 22:00, 02:00, 04:00, 06:00, and 11:00.ResultsDuring DIF, there was a significant decrease in the levels of cytokines, particularly, IL-1β and IL-6, in most measurements compared to non-fasting BL. This reduction was more obvious during the FOR period. There were no significant changes in the circadian phase of the measured cytokines reflected by the acrophase of the measured variables during fasting (FOR and Ramadan) compared to non-fasting BL.ConclusionUnder controlled conditions, DIF led to significantly decreased plasma levels of cytokines (IL-1β, IL-6, and IL-8), particularly IL-1β and IL-6 across 24 h. DIF had no effect on the circadian patterns of the measured cytokines as shown by cosinor analysis.

BACKGROUND:Food restriction has been demonstrated to increase the alertness in different species and to increase the levels of the wake-promoting neurotransmitter orexin. We hypothesized that diurnal intermittent fasting (DIF) increases orexin-A levels during fasting. Therefore, we conducted this study to assess the effects of DIF, during the month of Ramadan, on orexin, while controlling for lifestyle changes that may accompany Ramadan such as sleep duration, bedtime and wake time, energy expenditure, light exposure, and food.METHODS:Eight young healthy volunteers (mean age, 25.4 ± 3.5 years) reported to the laboratory on three occasions: (1) 4 weeks before Ramadan while performing DIF for 1 week outside the month of Ramadan (fasting outside Ramadan); (2) 1 week before Ramadan (nonfasting baseline) (BL); and (3) during the 2nd week of Ramadan while performing DIF (Ramadan). Plasma levels of orexin-A were measured using an enzyme immunoassay five times at 22:00, 02:00, 04:00, 06:00, and 11:00. Caloric intake, light exposure, and sleep schedule were maintained during the participants’ stays in the laboratory in the three study periods.RESULTS:Orexin-A levels increased in the daytime during fasting and decreased at night compared to BL. The differences in orexin-A levels between DIF and BL were significant at 06:00, 11:00, 22:00, and 02:00.CONCLUSIONS:DIF increases orexin-A levels in the plasma during fasting hours. This finding supports findings from animal studies showing that fasting increases alertness.

Purpose: We hypothesized that diurnal intermittent fasting would not increase slow frequency EEG waves, which reflect increased sleepiness. Therefore, this study aimed at performing a quantitative EEG analysis of young healthy volunteers with and without diurnal intermittent fasting while controlling for potential confounders. Methods: Eight young healthy volunteers (mean age: 24.4 ± 3.7 years) reported to the laboratory during the following five occasions: (1) adaptation, (2) 4 weeks before Ramadan while performing diurnal intermittent fasting (fasting from dawn to sunset) for 1 week (fasting outside Ramadan), (3) 1 week before Ramadan (nonfasting baseline), (4) during the second week of Ramadan while fasting (Ramadan), and (5) 2 weeks after Ramadan (recovery). Frontal, central, and occipital EEG signals were monitored four times (09:15, 11:15, 13:15, and 15:15 for 15 minutes each time) while the participants were awake to assess EEG spectral power of the delta, theta, alpha, and beta frequency bands. Results: During wakefulness, no difference in EEG slowing was observed between nonfasting baseline and fasting during and outside Ramadan. There were no differences in the mean absolute power of each band in any studied brain region in any of the four study periods. Moreover, there was no difference in EEG absolute powers in the delta, theta, alpha, and beta frequency bands for any individual brain region during the four study periods. Conclusions: Spectral analysis of EEG power indicates that diurnal intermittent fasting does not increase sleepiness. Future larger studies are needed to confirm the current findings.

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