The Effectiveness of Time-Restricted Eating as an Intermittent Fasting Approach on Shift Workers' Glucose Metabolism: A Systematic Review and Meta-Analysis

Background/Objectives: Shift workers face higher risks of impaired glucose metabolism due to irregular eating habits and circadian misalignment. Time-restricted eating (TRE) could improve glucose metabolism by aligning food intake with the circadian clock, but its effectiveness remains unclear. Methods: Ten electronic databases (PubMed, EMBASE, Cochrane Library, CINAHL, PsycINFO, Scopus, Web of Science, ProQuest Dissertations and Theses, Science.gov, and ClinicalTrials.gov) were searched from journal inception to September 2024. Only randomized controlled trials (RCTs) involving shift workers were included. Meta-analyses with sensitivity analyses were conducted using a random-effects model to pool glucose metabolism and sleep outcomes, with heterogeneity and quality assessments performed. Results: Six RCTs were included. TRE demonstrated positive but non-significant effects on glucose metabolism outcomes: fasting blood glucose (weighted mean difference [WMD]: -0.02 mmol/L, 95% confidence interval [CI]: -0.13 to 0.10, I2 = 0%), fasting blood insulin (WMD: -5.77 pmol/L, 95% CI: -85.62 to 74.08, I2 = 92%), HOMA-IR (WMD: -0.50, 95% CI: -2.76 to 1.76, I2 = 82%), 2 h postprandial glucose (WMD: -0.65 mmol/L, 95% CI: -3.18 to 1.89, I2 = 86%), total sleep time (g = 0.07, 95% CI: -0.23 to 0.37, I2 = 0%), and sleep efficiency (g = -0.05, 95% CI: -0.63 to 0.53, I2 = 62%). Sensitivity analyses yielded similar findings, and overall certainty of evidence was rated 'very low'. Conclusions: While TRE shows potential for improving the glucose metabolism in shift workers, current evidence remains inconclusive due to small sample sizes and study limitations. Future research should prioritize well-powered TRE RCTs in shift workers that adhere to a 6-10 h eating window. Incorporating early-TRE schedules with sleep hygiene may optimize metabolic outcomes, with circadian biomarkers analyzed to better elucidate the mechanistic pathway implicated.