Is Evening Carbohydrate Intake in Healthy Individuals Associated with Higher Postprandial Glycemia and Insulinemia When Compared to Morning Intake? A Systematic Review and Meta-Analysis of Randomized Crossover Studies

This systematic review aimed to summarize randomized clinical trials that compared the postprandial glycemic and insulinemic metabolic response after eating isocaloric and standardized carbohydrate meals consumed at two moments: morning versus night, in healthy individuals who were not shift workers. The search strategy consisted of an electronic search using the following electronic databases: MEDLINE (via PubMed), EMBASE (via Elsevier), LILACs (Virtual Health Library - VHL), Cochrane Registers of Clinical Trials (CENTRAL, via Wiley) and gray literature (Opengray.eu). The PICO strategy was used to define the search terms (P: healthy adults, I: nocturnal intake, C: morning intake, O: area under the curve (AUC) of the postprandial glucose and insulin response). This review was reported according to the PRISMA statement. From the 3757 articles found, 412 were duplicates and excluded, totaling 3345 that had their titles and abstracts read. A total of 42 articles met the inclusion criteria and were read in full, and eight studies were included in the systematic review. The certainty of the evidence was assessed using GRADE. The results showed, with moderate quality of evidence, a postprandial response with higher glycemic values in the evening compared to the morning (SMD = 1.30; 95% CI, 1.01 to 1.59; I = 0%;  < 0.00001; 8 studies and 116 participants). No differences were found between insulin values at night and in the morning (SMD = 0.19; 95% CI, -0.10 to 0.49; 6 studies and 90 participants). We concluded that the intake of carbohydrates at night leads to higher glycemic, but not insulinemic, postprandial values. Revision Record: PROSPERO number CRD42019137862 available at: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42019137862 Key teaching points and nutritional relevanceThis systematic review summarized randomized clinical trials that compared the postprandial glycemic and insulinemic response after eating carbohydrate meals in the morning versus at night.A total of eight studies were included in the systematic review; the results showed a postprandial response with higher glycemic values in the evening compared to the morning.No differences were found between insulin values at night and in the morning;• The intake of carbohydrates at night leads to higher glycemic, but not insulinemic, postprandial values.