Effects of time-restricted feeding with different feeding windows on metabolic health: A systematic review of human studies

•Studies of early and delayed time-restricted feeding in humans were compared for their metabolic health effects systematically.•Both early and delayed time-restricted feeding showed body weight-reducing effects.•Early and delayed time-restricted feeding differed in their effects on insulin sensitivity, blood lipids, body weight, and inflammatory factors. Time-restricted feeding (TRF), a feasible form of intermittent fasting, has been proven to benefit metabolic health in animal models and humans. TRF restricts the daily feeding window to 3 to 12 h for eating ad libitum, with fasting for the rest of the day. To our knowledge, specific guidance on the appropriate time period for eating during TRF has not yet been promoted. Therefore, the aim of the present review was to summarize the current literature on the effects of TRF with different eating windows in humans and compare their effects on metabolic health–related markers. Early TRF (which restricts food intake during the early period of the day) and delayed TRF (which restricts food intake during the later period of the day) studies have shown that both TRF regimens improve metabolic health in terms of reducing energy intake, decreasing body weight, improving insulin sensitivity, reducing blood pressure, and reducing oxidative stress. Differences between the consequences of early and delayed TRF were found, including differences in changes in blood lipid factors. These preliminary findings may help to provide guidance for choosing suitable eating windows during TRF. Future studies with rigorous designs and direct comparisons between the effects of TRF regimens with different eating windows on metabolic health markers are still needed.