How does diurnal intermittent fasting impact sleep, daytime sleepiness, and markers of the biological clock? Current insights

Figures & data

Figure 1 Lifestyle changes that accompany the month of Ramadan and that may affect sleep and circadian rhythms.

Table 1 A summary of the studies that objectively assessed changes in the circadian pattern of body temperature during diurnal intermittent fasting for Ramadan

Study	Study population	Study design	Assessment tool	Study setting	Findings	Study details
Roky et al^Citation25	8 healthy young adults (age: 20–28 years) Location: Morocco	Case crossover study with repeated measures	Rectal thermistor probe for at least 24 hours	Monitoring at home Controlled for meal composition and time, as well as bedtime and rising time	Delay in acrophase and bathyphase	The participants were of the intermediate chronotype as determined by the Morningness-Eveningness Questionnaire Dinner was served 1 hour before bedtime during Ramadan and 3 hours before bedtime at baseline No objective assessment of prior sleep pattern
Roky et al^Citation26	10 healthy young adults (age: 20–28 years) Location: Morocco	Case crossover study with repeated measures	High-precision medical oral thermometer at 09:00, 11:00, 13:00, 16:00, 20:00, and 23:00	Monitoring at home Controlled for meal composition and time, and bed and rise time	Reversal of circadian pattern of temperature	Subjects were of the intermediate chronotype as determined by the Morningness-Eveningness Questionnaire Sleep duration was 1 hour shorter during Ramadan than at baseline No objective assessment of prior sleep pattern
BaHammam et al^Citation30	8 healthy young adults (age: 31.8±2 years) Location: Saudi Arabia	Case crossover study with repeated measures	High-precision medical oral thermometer at 08:00, 16:00, and 00:00	Monitoring in the laboratory Controlled for meal composition	No change	No objective assessment of prior sleep pattern Subjects stayed in the laboratory during monitoring
BaHammam et al^Citation24	6 healthy young adults with delayed sleep phase disorder (age: 18–24 years) Location: Saudi Arabia	Case crossover study with repeated measures	SenseWear Pro Armband™ that measures proximal skin temperature during the last week of Shaban and the first 2 weeks of Ramadan	Free-living environment	Further delay in temperature acrophase	Subjects belonged to the evening chronotype Sleep patterns were monitored for 2 weeks prior to the study by using sleep diaries (no objective assessment) Sleep/wake schedule and sleep duration during the study were assessed objectively via armband Participants lived in an unconstrained environment during the study

Table 2 A summary of the studies that objectively assessed changes in melatonin during diurnal intermittent fasting for Ramadan

Study	Study population	Study design	Assessment tool	Study setting	Findings	Study details
Bogdan et al^Citation27	10 healthy male volunteers (age: 32–40 years) Location: France	Case crossover study with repeated measures	Blood samples were obtained every 4 hours, omitting the 02:00 time point, before and on the 23rd day of Ramadan	Free-living environment Controlled for meal timing and composition Did not control for light exposure, sleep schedule, or social habits that accompany Ramadan	A decreased and delayed night peak and a flattened slope of serum melatonin concentration in Ramadan	Volunteers slept 1 hour less during Ramadan than before Ramadan Melatonin concentrations were not measured late at night, which fails to address the possibility of a late peak in melatonin concentration
BaHammam et al^Citation30	8 healthy young adults (age: 31.8±2 years) Location: Saudi Arabia	Case crossover study with repeated measures	Saliva samples were collected at three time points over a 24-hour period (08:00, 16:00, and 00:00) before and on the 7th and 21st days of Ramadan	In-laboratory monitoring Controlled for meal timing and composition Controlled for sleep duration Did not control for light exposure or social habits that accompany Ramadan	A significant decrease in melatonin concentrations at 00:00 and 16:00 during Ramadan Melatonin profiles continued to show the same trend during Ramadan, but with a flatter slope	Melatonin concentrations were not measured late at night, which fails to address the possibility of a late peak in melatonin concentration
Almeneessier et al^Citation28	8 healthy young adults (age: 26.6±4.9 years) Location: Saudi Arabia	Case crossover study with repeated measures	Blood samples were collected at 22:00, 02:00, 04:00, 06:00, and 11:00 before Ramadan and while performing fasting outside Ramadan month and on the second week of Ramadan	In-laboratory monitoring Controlled for light exposure, sleep schedule, sleep duration, energy expenditure, and meal composition	Intermittent fasting during Ramadan has no significant effect on the circadian pattern of melatonin	Assessed melatonin level when volunteers were fasting outside Ramadan month to control for lifestyle changes that accompany Ramadan

Table 3 A summary of the studies that assessed sleep architecture using polysomnography during diurnal intermittent fasting for Ramadan

Study	Study population	Study design	Test used for assessment	Study details	Findings
Roky et al^Citation25	8 young healthy adults (age: 20–28 years) Location: Morocco	Case crossover study with repeated measures	Ambulatory 8-channel unattended PSG	Unattended PSG Dinner was served at 22:30, and PSG recording started at 23:30 Did not objectively account for the prior sleep/wake pattern before assessing sleep Did not monitor for daytime naps prior to overnight sleep study Meals during and outside Ramadan were according to a fixed schedule and composition	Significant increase in sleep latency and reduction in total sleep time Increase in stage N2 and reduction in slow wave sleep Reduced REM sleep
BaHammam et al^Citation30	8 young healthy adults (age: 31.8±2 years) Location: Saudi Arabia	Case crossover study with repeated measures	Full attended level 1 in-laboratory PSG	Controlled for sleep schedule, naps, and caloric intake Did not objectively account for the prior sleep/wake pattern before assessing sleep in the laboratory	Significant drop in sleep latency at the end of Ramadan, with no change in total sleep time Reduced REM sleep at the end of Ramadan No significant changes in NREM sleep
BaHammam et al^Citation44	8 young healthy adults (age: 26.6±4.9 years) Location: Saudi Arabia	Case crossover study with repeated measures	Full attended level 1 in-laboratory PSG	Controlled for sleep schedule, naps, light exposure, caloric intake, and energy expenditure Assessed the effect of fasting during and outside Ramadan Controlled for sleep/wake and naps for 2 weeks before assessing sleep in the laboratory via actigraphy	Reduced REM sleep during intermittent fasting (during and outside Ramadan) No significant changes in NREM sleep No differences in sleep latency, arousal index, or sleep efficiency
Chamari et al^Citation43	11 young healthy trained cyclists (age: 21.6±4.8 years) Location: Qatar	Case crossover study with repeated measures	Portable PSG	Unattended PSG Did not control for sleep/wake pattern or sleep duration During Ramadan, volunteers slept during daytime and at night before and after Ramadan During Ramadan, the volunteers slept in the morning after eating a main meal Naps were not controlled for Did not account for the prior sleep/wake pattern before assessing sleep Participants were cyclists at a training camp The portable device used in the study had relative weakness at the level of the number of awakenings Data regarding sleep duration were highly heterogeneous	No change in sleep duration Significant increases in the number of awakenings and light sleep in Ramadan Progressive decrease in duration of sleep and REM sleep stages that became significant 2 weeks after Ramadan

Abbreviations: NREM, nonrapid eye movement sleep; PSG, polysomnography; REM, rapid eye movement sleep.

Table 4 A summary of the studies that assessed daytime sleepiness and daytime alertness during diurnal intermittent fasting for Ramadan

Study	Study population	Study design	Assessment tool	Findings	Study details
Subjective assessment
BaHammam et al^Citation21	56 healthy medical students (age: 22.6±1.3 years) Location: Saudi Arabia	Case crossover study with repeated measures	ESS	Increase in daytime sleepiness	Subjective assessment Assessment was conducted in an unconstrained environment
Benchekroun et al^Citation40	264 young subjects (age: 20–30 years) Location: Morocco	Case crossover study with repeated measures	ESS	Increase in daytime sleepiness	Subjective assessment Assessment was conducted in an unconstrained, free-living environment
BaHammam et al^Citation23	101 healthy fasting and nonfasting subjects (age: 31.3±2.1 years) Location: Saudi Arabia	Case-control study with repeated measures	ESS	No change in daytime sleepiness	Subjective assessment Assessment was conducted in an unconstrained, free-living environment
Margolis et al^Citation39	109 healthy medical students (age: 19–23 years) Location: United Arab Emirates	Case crossover study with repeated measures	ESS	No change in daytime sleepiness	Subjective assessment Assessment was conducted in an unconstrained, free-living environment
Nugraha et al^Citation52	Among young healthy adults Fasting group (n=25) (age: 26.12±0.98 years); nonfasting group (n=25) (age: 26.2±0.98 years) Location: Germany	Case-control with repeated measures	ESS	No difference in daytime sleepiness between the two groups However, the ESS score among the fasting group was significantly lower in the last week of Ramadan than in the first week	Subjective assessment Assessment was conducted in an unconstrained, free-living environment
Objective assessment
Roky et al^Citation26	10 healthy young subjects (age: 20–28 years) Location: Morocco	Case crossover study with repeated measures	Visual analog scale MRT CFF All measurements taken at 6 different times of the day: 09:00, 11:00, 13:00, 16:00, 20:00, and 23:00	Decreased daytime alertness MRT increased at the beginning of Ramadan CFF did not change	Controlled for sleep/wake pattern Volunteers slept 1 hour less during Ramadan than at baseline Controlled for meal composition and physical activity
BaHammam et al^Citation42	16 fasting and nonfasting subjects 8 fasting (age: 36.25±4.46 years) 8 nonfasting (age: 34.75±3.33 years) Location: Saudi Arabia	Case-control with repeated measures	Johns Drowsiness Scale to assess sleepiness Visual reaction time test ESS	No decrease in alertness No change in daytime sleepiness	Assessed sleep duration objectively using the SenseWear Pro Armband^™. There was a significant reduction in sleep duration during Ramadan in the fasting group Assessment was conducted in an unconstrained environment
BaHammam et al^Citation61	8 healthy young male subjects (age: 25.3±2.9 years) Location: Saudi Arabia	Case crossover study with repeated measures	Johns Drowsiness Scale IR for total blink duration and a visual reaction time test	No decrease in alertness	Controlled for sleep/wake schedule, sleep duration, caloric intake, energy expenditure, and light exposure Actigraphy to assure adequate sleep duration in days prior to the study
Chamari et al^Citation43	11 young healthy trained cyclists (age: 21.6±4.8 years) Location: Qatar	Case crossover study with repeated measures	CANTAB, RTI, and RVP tests	No decrease in alertness RTI was not affected by Ramadan intermittent fasting or time of day Overall, RVP accuracy increased during and after Ramadan compared with baseline; in the last week of Ramadan, accuracy was highest at the end of the day	Sleep duration was not assessed during the 24 hours Tests were conducted at different times during and outside Ramadan
Roky et al^Citation51	8 healthy young subjects (age: 20–28 years) Location: Morocco	Case crossover study with repeated measures	Portable MSLT Visual analog scale	Increase in daytime sleepiness Subjective alertness decreased at 12:00 on day 11 of Ramadan but did not change on day 25 On the MSLT, sleep latency was decreased on day 11 and day 25 of Ramadan	Portable device used; programmed to end test after 20 minutes of recording Sleep duration was significantly lower during Ramadan than at baseline Meals during baseline and Ramadan followed a fixed schedule and composition Did not rule out possible sleep deprivation in nights prior to study
BaHammam et al^Citation30	8 healthy young subjects (age: 31.8±2 years) Location: Saudi Arabia	Case crossover study with repeated measures	ESS and standard MSLT	No change in daytime sleepiness	Did not rule out possible sleep deprivation in nights prior to study MSLT was preceded by an overnight in-laboratory PSG
BaHammam et al^Citation44	8 healthy young subjects (age: 26.6±4.9 years) Location: Saudi Arabia	Case crossover study with repeated measures	ESS and standard MSLT Actigraphy to assess sleep duration in days prior to the study	No change in daytime sleepiness during Islamic intermittent fasting	Sleepiness was assessed while the volunteers were performing intermittent fasting during and outside Ramadan Controlled for sleep duration in nights prior to study and when at home by objective measurements (actigraphy)
Tian et al^Citation62	18 male athletes (age: 17–29 years) Location: Singapore	Case crossover study with repeated measures	Computerized neuropsychological testing	Performance in functions requiring sustained rapid responses was best in the morning and declined in the late afternoon Performance in nonspeed-dependent accuracy measures was more resilient	Standardized meals were provided Participants’ lifestyle and training in-between test sessions were not controlled for Sleep duration was significantly shorter during Ramadan than at baseline Previous night’s sleep and daytime naps, as well as the time of awakening, were not controlled for in this study Participants answered questionnaires regarding diet and sleep duration in the previous 24 hours

Abbreviations: CANTAB, Cambridge Neuropsychological Test Automated Battery; CFF, critical flicker fusion; ESS, Epworth Sleepiness Scale; IR, infrared reflectance; MRT, movement reaction time; MSLT, multiple sleep latency test; PSG, polysomnography; RTI, Reaction Time Index; RVP, Rapid Visual Information Processing.

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