Olive by-products and cardiometabolic health: a GRADE meta-analysis
مستخلصات الزيتون والصحة الأيضية: مراجعة منهجية وتلخيص بيانات
Journal: Nutrition, metabolism, and cardiovascular diseases : NMCD
University: Multiple institutions (systematic review)
Study Type: meta-analysis
Evidence Level: moderate
Participants: 1726
Published:
30-Second Summary
This GRADE-assessed systematic review and meta-analysis pooled 30 randomized controlled trials (n=1,726) that tested olive leaf or olive pomace supplements on 21 cardiometabolic and anthropometric biomarkers. The authors report modest, outcome-specific effects for some markers, with certainty of evidence varying across outcomes and some inconsistency between trials.
1-Minute Summary
The study is a GRADE-assessed systematic review and random-effects meta-analysis of 30 randomized controlled trials (total n=1,726) examining olive leaf (OL) or olive pomace (OP) supplementation on 21 standardized biomarkers including lipids, glycemic measures, inflammatory markers, blood pressure and anthropometrics. Meta-analyses were performed using random-effects models and the certainty of evidence was graded per outcome. Results indicate modest, outcome-specific changes in some cardiometabolic markers, but effects were not uniform across all outcomes and between trials. The authors highlight heterogeneity and variable evidence certainty, recommending cautious interpretation and further high-quality trials for outcomes with low or inconsistent certainty.
3-Minute Summary
This GRADE-assessed systematic review and meta-analysis pooled results from 30 randomized controlled trials (total n=1,726) investigating olive leaf (OL) or olive pomace (OP) supplementation and effects on cardiometabolic and anthropometric biomarkers. Trials evaluated 21 standardized outcomes across lipid profile, inflammatory markers, glycemic control, insulin sensitivity, blood pressure, and anthropometry. Random-effects meta-analyses found modest, outcome-specific improvements: small reductions in systolic and diastolic blood pressure in some trials, modest favorable shifts in certain lipid fractions, and limited improvements in markers of inflammation and glycemia in subsets of studies. Effect sizes were generally small and not consistent across all outcomes. The GRADE assessment rated certainty of evidence as low to moderate depending on outcome, with downgrades due to heterogeneity, risk of bias, imprecision, and variability in formulations, doses, and intervention duration. Subgroup and sensitivity analyses were limited by study reporting and heterogeneity. Overall, OL/OP supplementation may support modest improvements in select cardiometabolic risk markers, but current evidence is insufficient to draw definitive conclusions. Further well-powered, standardized trials using transparent reporting of olive by-product composition, dose-response, and long-term clinical endpoints are needed to clarify effects. Meanwhile, clinicians and consumers should interpret current findings cautiously and prioritize established lifestyle strategies for cardiometabolic health and prevention.
Full Analysis
Background and scope: This systematic review and meta-analysis synthesized randomized controlled trial evidence on olive leaf (OL) and olive pomace (OP) supplementation and 21 standardized cardiometabolic and anthropometric biomarkers. Thirty trials (n=1,726) were included, with interventions varying in extract source, phenolic content, dose, and duration. Main quantitative findings: Random-effects meta-analyses identified small, outcome-specific effects. Pooled estimates suggested modest reductions in systolic and diastolic blood pressure in some trials, and modest improvements in specific lipid fractions (for example, reductions in LDL-cholesterol or improvements in HDL-related measures in selected studies). Effects on fasting glucose, HbA1c, and insulin resistance indices were generally inconsistent and limited to subsets of trials. Inflammatory markers showed minor, heterogeneous changes. Overall effect sizes were small, often with confidence intervals crossing clinically important thresholds. Quality and heterogeneity: The GRADE assessment rated evidence certainty from low to moderate across outcomes. Common reasons for downgrading included study heterogeneity (I2 variability), risk of bias related to allocation concealment and blinding in several trials, imprecision from small sample sizes, and indirectness stemming from variable supplement formulations. Publication bias could not be excluded for some outcomes. Limitations of the evidence base: Trials differed substantially in OL/OP composition (total phenolics, oleuropein, hydroxytyrosol), dosage regimens, co-interventions, and participant baseline risk. Short duration in many trials limits inference about sustained cardiometabolic effects. Reporting gaps impeded dose–response assessment and subgroup exploration by baseline risk or concomitant medications. Implications for research: Future RCTs should preregister protocols, use standardized reporting of olive by-product composition, include adequately powered samples, longer follow-up, and prespecified subgroup and dose-response analyses. Mechanistic outcomes (e.g., bioavailability, microbiome interactions) would clarify pathways. Clinicians and policymakers should interpret current pooled estimates cautiously. Additional attention to participant dietary background, medication use, and validated outcome measurement would strengthen causal inference and improve external validity across populations, and longer intervention durations.Health Implications
For everyday habits, this evidence suggests that incorporating whole-food sources of olive phenolics—such as olives and extra virgin olive oil—within a varied, plant-rich dietary pattern may support cardiovascular and metabolic health markers alongside established behaviors. Regular physical activity, weight management, smoking cessation, and limiting processed foods and added sugars remain primary determinants of cardiometabolic risk. If considering olive leaf or pomace supplements, recognize product variability and consult healthcare professionals; supplements may offer modest benefits for specific biomarkers but should complement, not replace, balanced diet and proven lifestyle measures. Prioritize consistent sleep, stress management, and routine preventive care regularly with professionals.
Key Findings
- Pooled data from 30 RCTs (n=1,726) showed modest, outcome-specific improvements in some cardiometabolic biomarkers (e.g., certain lipid measures and blood pressure components), but effects were not consistent across all outcomes.
- GRADE assessment indicated variable certainty across outcomes (ranging from low to moderate); heterogeneity between trials and differences in supplement formulations, doses and durations limit confidence in some pooled estimates.