The Effect of Different Types of Olive Oil on Glucose Control and Insulin Sensitivity: A GRADE-Assessed Systematic Review and Dose-Response Meta-Analysis of 51 Randomized Controlled Trials

Abstract Background Olive oil as food is composed mainly of fatty acids and bioactive compounds with diverse and attractive biological activities that have an inverse relationship with insulin resistance and diabetes-related factors. However, the results of available clinical trials are inconsistent. Therefore, we summarized 51 randomized controlled trials (RCTs) and evaluated the association of olive oil intervention with glycemic control in adults. Methods A comprehensive literature search of the PubMed, Scopus, and ISI Web of Sciences databases was performed to identify RCTs investigating the effect of different olive oil types on any glycemic profile component. Quantitative data were synthesized using either a fixed or random-effects model, with a weighted mean difference (WMD) and 95% CI for analysis. Results In the primary search, 2705 articles were found, of which 115 were assessed in full text, and 51 trials (n = 4334 participants) were included in the meta-analysis. We found the consumption of olive oil was not associated with statistically significant changes in blood glucose (WMD = –0.04 mg dL–1; 95% CI, –0.1 to 0.02; P = .18; I2 = 27.05%), insulin (WMD = –0.3 µIU mL–1; 95% CI, –0.99 to 0.38; P = .39; I2 = 91.49%), hemoglobin A1c (HbA1c) (WMD = 0.02%, 95% CI, –0.01 to 0.06; P = .21; I2 = 0%) and Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) (WMD = –0.09; 95% CI, –0.25 to 0.06; P = .26; I2 = 73.13%). The nonlinear dose-response analysis showed a significant association between the olive dose and HOMA-IR (P = .024 for nonlinearity). Also, the duration of olive oil intervention showed a significant nonlinear relationship with HOMA-IR (P = .025 for nonlinearity), insulin (P = .002 for nonlinearity), and HbA1c (P = .048 for nonlinearity) in dose-response analysis. Conclusions Our comprehensive review and meta-analysis of 51 RCTs indicate that olive oil consumption by adults does not significantly affect overall glycemic control. However, a daily dose of 25-50 g significantly improves the HOMA-IR parameter, suggesting a potential benefit for diabetes management. These findings highlight the need for further research to fully understand the practical implications of olive oil consumption in diabetes care. Systematic Review Registration PROSPERO registration No. CRD42023459523