Impact of intermittent fasting on sleep physiology: A prospective observational study using smartwatch technology

Time-restricted eating (TRE) following a 16:8 pattern is a popular form of intermittent fasting with established metabolic benefits. However, its impact on sleep and physical activity remains unclear, particularly when assessed using wearable technologies. This study investigated the short-term effects of TRE on sleep physiology and activity levels by using a commercially available smartwatch. In this prospective observational study, 35 healthy adults (mean age, 30 years; 66% female) completed a 3-day baseline phase, followed by 7 days of a 16:8 TRE regimen. Objective data on sleep, heart rate, and activity were continuously recorded using Withings ScanWatch. Subjective sleep quality, including the Pittsburgh Sleep Quality Index, was assessed pre- and postintervention. Statistical analyses were performed using paired t tests. No significant changes were observed in total sleep duration, light or deep sleep, sleep latency, or nocturnal awakenings between baseline and fasting periods. The daily step count, energy expenditure, and heart rate parameters remained stable. A nonsignificant trend towards slightly reduced deep sleep was noted, which is consistent with the results of previous studies. Subjective sleep assessments reflected objective data, with most participants reporting no perceived changes in sleep quality during intermittent fasting. Short-term 16:8 intermittent fasting did not significantly affect the sleep physiology, physical activity, or heart rate in healthy adults. The subjective and objective measures were closely aligned. These findings support those of previous reviews suggesting that TRE does not influence sleep architecture in healthy populations. Further studies are needed in metabolically at-risk cohorts over longer durations.