Effects of timing of meal intake on glucose metabolism: a systematic review and meta-analysis of human intervention studies

Aims: This systematic review and meta-analysis aims to summarize the effect of the timing of meal intake on glycaemic outcomes in human intervention studies. Data synthesis: Medline and Embase.com were searched for intervention studies in the adult population directly comparing the timing of meal intake on glycaemic outcomes. Results were meta-analysed in random-effects models or qualitatively described using vote counting. Of 55,569 publications screened, 44 studies were included. Study duration was up to one week (n = 37) or 2-12 weeks (n = 7). Shorter studies demonstrated that early meal timing, compared to late meal timing, significantly lowers postprandial 2-h glucose (-1.51 [-2.03, -0.99] mmol/L, I² = 79%) and postprandial peak glucose (-1.03 [-1.63, -0.44] mmol/L, I² = 61%). Mean glucose over 24-h, largest glucose peak over 24-h, fasting glucose, fasting insulin and postprandial 2-h insulin also showed the same direction, albeit not significant. In longer studies, fasting glucose seemed lower in early meal timing (-0.05 [-0.13, 0.02] mmol/L, I² = 27%). Conversely, fasting insulin and HOMA-IR showed no differences. Conclusions: This systematic review and meta-analysis shows physiological plausibility that early meal intake may be beneficial for glycaemic control, compared to late meal intake. However, this is only seen in studies with a duration of up to one week. Moreover, the high heterogeneity between study designs, interventions, and methods precludes definite conclusions and clinical recommendations. Larger and longer trials, that control for total energy intake, weight loss, and rhythms of other Zeitgebers, are needed before chrono-nutrition principles can be translated into clinical dietary guidelines for glycaemic control.