Cardiometabolic status among shift workers under meal time regulation: A systematic review of randomized controlled trials

To date, findings have denoted that disrupted meal timing and eating during biologically inappropriate hours are associated with an increased risk of adverse cardiometabolic outcomes among shift workers. However, solid evidence remains lacking due to the small number of clinical studies and low methodological quality. This review investigated how an intervention targeting shift workers' meal timing affects cardiometabolic markers. The MEDLINE, Cochrane Library, Web of Science, Embase, CINAHL Complete, and Scopus were searched using a predefined search strategy. Only randomized controlled trials of adults aged ≥18 under a shift work environment were included. Four trials met the inclusion criteria. Three studies assigned fasting periods during the night shift, ranging between 19:45 and 06:30 h, and one study used 10-h self-selected Time-Restricted Eating (TRE). A 10 h self-selected TRE reported a significantly lower VLDL-C particle size compared with the control group. Four studies reporting fasting insulin levels and homeostatic model assessment of insulin resistance observed a significant change in one trial after an 8.5-h overnight fast. No studies pointed to significant changes in HDL-C. In the postprandial measurement, 10.75 h of night fasting showed significantly lower glucose AUC, non-esterified fatty acids AUC, and 2-h glucose than in the meal- and snack-at-night group. Body weight was slightly lower after a short overnight fast. The scarcity of trials investigating mealtime interventions and cardiometabolic markers among shift workers limits the generalizability of the findings and raises concerns regarding the robustness of the preliminary positive outcomes. Therefore, more trials with larger sample sizes and longer study durations are required, given the limited number of studies.