Effects of Ramadan intermittent fasting on sleep, cognitive and physical performance in elite karate athletes: A within-subject repeated-measures study.

Ramadan intermittent fasting alters sleep-wake patterns, dietary intake, and daily routines, which may interact with circadian timing and fatigue to influence athletic performance. This study examined the effects of Ramadan fasting on sleep, dietary intake, cognitive performance, and anaerobic running performance across different times of day and fatigue states in elite karate athletes. Twelve elite male karate athletes completed a within-subject repeated-measures protocol before Ramadan, during the second week, and during the fourth week of Ramadan. Testing was conducted at 08:00, 17:00, and 22:00. Simple reaction time, multiple-choice reaction time, Stroop performance, and 5-m multiple shuttle run performance were assessed before and after a karate-specific aerobic fatigue protocol. Sleep and dietary intake were monitored throughout each period. Ramadan fasting significantly reduced total sleep time, sleep efficiency, total energy intake, carbohydrate intake, and fat intake, while increasing subjective sleepiness and fatigue. Cognitive and physical performance were significantly affected by Ramadan period, time of day, and fatigue state. The greatest deterioration occurred during the fourth week of Ramadan, particularly at 17:00, when both reaction-time performance and shuttle-run outcomes showed the largest impairments compared with pre-Ramadan values. Performance decrements were also observed at 22:00, whereas morning performance at 08:00 was relatively preserved. Exercise-induced fatigue further worsened cognitive and physical outcomes and attenuated normal time-of-day variation. These findings indicate that Ramadan intermittent fasting induces sleep disruption, dietary alterations, and time-of-day dependent impairments in elite karate athletes. The late afternoon, particularly 17:00 during the fourth week of Ramadan, appears to be the most vulnerable period for cognitive and physical performance deterioration, especially under fatigue. Training load, recovery strategies, sleep management, and nutritional timing should therefore be carefully adapted during Ramadan.