Olive leaf and pomace supplements: a GRADE-rated meta-analysis of cardiometabolic biomarkers
تحليل تلوي مُقيّم حسب GRADE لمكملات أوراق وزفالة الزيتون والمؤشرات الأيضية القلبية
Journal: Nutrition, metabolism, and cardiovascular diseases : NMCD
University: Multiple institutions
Study Type: meta-analysis
Evidence Level: high
Participants: 1726
Published:
30-Second Summary
This GRADE-assessed systematic review and meta-analysis pooled 30 randomized controlled trials (n=1726) evaluating olive leaf or olive pomace supplementation on 21 cardiometabolic and anthropometric biomarkers. The authors report heterogeneous, generally modest effects across outcomes, with certainty varying by outcome according to GRADE.
1-Minute Summary
The study synthesized data from 30 RCTs (total n=1726) testing olive leaf or olive pomace supplements against placebo or control on 21 standardized biomarkers including lipids, glycemic measures, blood pressure, inflammatory markers, insulin sensitivity, and anthropometrics. Meta-analyses used random-effects models and outcomes were graded using GRADE. Results were heterogeneous across biomarkers; some outcomes showed statistically significant differences while many showed small or inconsistent effects. The authors highlight variable certainty of evidence, with limitations related to heterogeneity, study quality, and outcome reporting.
3-Minute Summary
This GRADE-assessed systematic review and meta-analysis pooled 30 randomized controlled trials (n = 1,726) investigating olive leaf (OL) or olive pomace (OP) supplementation and effects on 21 standardized cardiometabolic and anthropometric biomarkers. Trials varied in population, extract type, dose, and duration. Random-effects meta-analyses found generally modest, heterogeneous effects: some lipid outcomes (eg, small reductions in LDL-cholesterol and total cholesterol) and selected glycemic measures (eg, modest improvements in fasting glucose or HOMA-IR in specific subgroups) reached statistical significance, while many inflammatory markers, anthropometric outcomes (weight, BMI, waist circumference), and blood pressure showed inconsistent or null pooled effects. The GRADE appraisal judged certainty as moderate for a subset of lipid and glycemic outcomes, but low or very low for many inflammatory and anthropometric endpoints, driven by inconsistency, imprecision, and study limitations (small sample sizes, short follow-up, variable preparations). Sensitivity and subgroup analyses (OL vs OP, dose, duration) suggested effect heterogeneity but were limited by sparse data. Overall, the evidence suggests olive by-product polyphenol supplementation may support modest improvements in certain lipid and glycemic markers, but conclusions are tempered by trial heterogeneity and methodological limitations; further well-powered, standardized trials with longer follow-up are needed.
Full Analysis
This meta-analysis synthesized 30 randomized controlled trials (total n = 1,726) assessing olive leaf (OL) or olive pomace (OP) supplementation effects on 21 predefined cardiometabolic and anthropometric biomarkers, including lipids, glycemic indices, inflammatory markers, blood pressure, and anthropometry. Inclusion criteria prioritized RCT design and standardized outcome reporting. Trials displayed substantial clinical and methodological heterogeneity: participant health status ranged from healthy volunteers to metabolic-risk groups, preparations varied from crude leaf infusions to concentrated phenolic extracts, doses and polyphenol content were inconsistently reported, and follow-up spanned weeks to months. Random-effects models were appropriate given heterogeneity; pooled effect estimates were generally small. Statistically significant pooled reductions were observed for selected lipid parameters (notably modest decreases in LDL-cholesterol and total cholesterol) and for some glycemic measures in subgroup analyses, but effect sizes were often clinically small and accompanied by moderate-to-high I2 values, indicating inconsistency. Many inflammatory markers (eg, CRP, IL-6) and anthropometric outcomes showed null or inconsistent pooled effects. Risk-of-bias concerns (allocation concealment, blinding, incomplete outcome data), small individual study sizes, short durations, and variable reporting undermined confidence. The authors applied GRADE: moderate certainty for a subset of lipid and glycemic outcomes, but low/very low certainty for many inflammatory and anthropometric endpoints due to imprecision and inconsistency. Publication bias was not definitively excluded. Mechanistic plausibility rests on olive phenolics’ antioxidant and anti-inflammatory properties and possible insulin-sensitizing effects, but translation to clinical endpoints is unproven. Future trials should standardize extract characterization, report polyphenol content, use adequate sample sizes and durations, assess clinically relevant endpoints, and explore dose–response and gut microbiome–mediated mechanisms.Health Implications
For daily habits, emphasize whole-diet approaches rather than single supplements. Incorporating polyphenol-rich foods (olive products, fruits, vegetables, tea) within a Mediterranean-style pattern, alongside high-fiber plant foods, regular physical activity, adequate sleep, and smoking avoidance, may support cardiometabolic health. If considering olive leaf or pomace supplements, choose well-characterized products, discuss with a clinician especially if taking medications, and view them as adjuncts to—not replacements for—established lifestyle measures. Regular monitoring of lipids, glucose, weight, and blood pressure remains important.
Key Findings
- The meta-analysis included 30 RCTs (n=1726) assessing 21 cardiometabolic and anthropometric biomarkers; pooled effects were heterogeneous and generally modest, with some statistically significant differences reported for select lipid and glycemic outcomes.
- GRADE assessment indicated variable certainty across outcomes—moderate certainty for some lipid and glycemic measures and low or very low certainty for many inflammatory and anthropometric outcomes—citing heterogeneity and study limitations.