Metabolic and inflammatory effects of oleuropein and olive leaf extract: a systematic review and meta-analysis

Background: Olive leaves, a by-product of olive oil production, are rich in oleuropein, a phenolic compound with antioxidant and anti-inflammatory properties. This systematic review and meta-analysis evaluated the effects of olive leaf extract (OLE) and oleuropein on glucose metabolism, lipid profile, and inflammatory markers in randomized clinical trials (RCTs). Methods: The review was registered in PROSPERO (CRD42022375615) and followed PRISMA guidelines. PubMed, Scopus, and Web of Science were searched up to January 2026 without restrictions. Eligible studies were RCTs in adults comparing OLE or oleuropein with placebo or control. Study selection, data extraction, and risk of bias (RoB 2) assessment were performed independently by two reviewers; certainty of evidence was assessed with GRADE. Meta-analyses were conducted when at least two trials reported suitable data. Results: Eleven RCTs were included (4 short-term and 7 continuous-intake trials). Short-term crossover studies showed heterogeneous effects on postprandial glycemia and insulin responses, precluding meta-analysis. In continuous-intake, parallel-design RCTs, pooled analyses demonstrated no statistically or clinically significant effects on glycemic or lipid outcomes. Evidence regarding inflammatory markers was scarce and of low certainty. Conclusion: The current evidence does not support clinical recommendations for OLE supplementation aimed at health benefits. Data from methodologically consistent and robust trials indicate no statistically significant metabolic or inflammatory effects under usual human consumption patterns, whereas evidence from other study designs remains inconclusive. Further high-quality RCTs are required to clarify potential metabolic benefits.