The Effect of Early Time-Restricted Feeding on Glycemic Profile in Adults: A Systematic Review of Interventional Studies

BACKGROUND Early time-restricted feeding (eTRF) is a new dietary strategy, involving extended fasting (>14h) from midafternoon onwards with or without calorie restriction. Most of the published studies indicate controversial effects on several glycemic markers. AIM To evaluate the effect of non-calorie restricted eTRF on the glycemic profile of adults. METHOD this systematic review was designed according to PRISMA guidelines. Pubmed/ Medline, the Cochrane library and EBSCO electronic databases were systematically searched for eligible clinical trials. Studies with eTRF or with daily fasting regimens that presented all the characteristics of eTRF were selected and compared with regular diet schedules or delayed time-restricted feeding. Blood glucose and insulin markers were extracted from each study as the main outcome measures. RESULTS Five articles including 67 adult subjects in total were selected. The period of intervention varied between 3 days to 5 weeks. Three of the included studies were diet- controlled for weight maintenance, whereas the other two studies allowed for free living. Quality assessment identified two studies of low and three studies of high risk of bias. two studies showed clear positive effects of eTRF on both glucose and insulin markers, including fasting glucose levels, muscle glucose intake, glucose iAUC responses insulin levels, and insulin resistance (p<0.05). Two other studies showed beneficial effects on glucose markers only (fasting glucose, 24h mean glucose levels, and iAUC responses, p<0.05) and the fifth study showed positive effects on insulin markers only (insulin resistance, p<0.05). CONCLUSIONS eTRF seems to have positive effects on the glycemic profile mainly in healthy individuals with normal BMI. However, other factors should also be taken into account to address overweight, obese, and prediabetic individuals. Further research is required to clarify better the effectiveness of eTRF among individuals with different characteristics.