A GRADE-assessed systematic review and meta-analysis of randomized controlled trials evaluating the effects of olive leaf or olive pomace supplementation on cardiometabolic and anthropometric health markers

Aims Cardiometabolic diseases (CMDs) are major contributors to global morbidity and mortality, and dietary bioactives such as polyphenols may modulate key risk factors. Olive by-products, particularly olive leaves (OL) and olive pomace (OP), are rich in phenolic compounds with antioxidant, anti-inflammatory, and cardiometabolic effects demonstrated across in vitro, preclinical, and clinical studies. Data synthesis This GRADE-assessed systematic review and meta-analysis included 30 randomized controlled trials (n = 1,726) evaluating OL or OP supplementation on 21 standardized biomarkers, encompassing inflammatory markers, lipid profile, glycemic control, insulin sensitivity, anthropometric measures, and blood pressure. Meta-analyses were conducted using random-effects models, with effect sizes calculated as mean differences (or standardized mean differences for oxLDL). Between-study heterogeneity was assessed with I2 statistics, and sensitivity and subgroup analyses explored potential sources of variability. Publication bias was evaluated using Begg’s test and funnel plots where appropriate. OL supplementation significantly improved lipid parameters (total cholesterol, triglycerides, LDL-C, ApoB, oxLDL) and increased ApoA1, while reducing TNF-α, systolic and diastolic blood pressure, body weight, and BMI. No significant effects were observed on glycemic markers. OP supplementation showed no consistent cardiometabolic benefits and was associated with an increase in IL-8. Certainty of evidence ranged from very low to high, with several outcomes downgraded due to imprecision, heterogeneity, or limited study numbers. Conclusion These findings support the targeted use of OL as an adjunctive strategy for cardiometabolic risk management. Evidence for OP supplementation remains limited, underscoring the need for well-powered, high-quality RCTs to clarify its clinical effects.