Olive leaf and pomace supplements: a GRADE-assessed meta-analysis on cardiometabolic markers
مكملات ورق ومخلفات الزيتون: تحليل تلوي مُقَيَّم بـGRADE لعوامل صحية قلبية أيضية
Journal: Nutrition, metabolism, and cardiovascular diseases : NMCD
University: Not specified
Study Type: meta-analysis
Evidence Level: high
Participants: 1726
Published:
30-Second Summary
This is a GRADE-assessed systematic review and random-effects meta-analysis of 30 randomized controlled trials (n=1,726) examining olive leaf and olive pomace supplementation across 21 cardiometabolic and anthropometric biomarkers. The review reports variable, generally modest effects on some lipid, glycemic, inflammatory and body-measure outcomes, with heterogeneity and varying certainty across outcomes.
1-Minute Summary
The paper pooled data from 30 randomized controlled trials (total n=1,726) to evaluate the impact of olive leaf (OL) and olive pomace (OP) supplementation on 21 standardized biomarkers related to inflammation, lipids, glycemic control, insulin sensitivity, anthropometry, and blood pressure. Analyses used random-effects models and outcomes were rated using GRADE. Across outcomes the authors report modest improvements for some lipid, glycemic and inflammatory markers and small changes in anthropometric measures, but effects were heterogeneous and certainty varied by outcome. The authors emphasize the need to interpret results cautiously due to between-study heterogeneity and varying evidence certainty.
3-Minute Summary
This GRADE-assessed systematic review and meta-analysis synthesized evidence from 30 randomized controlled trials (n = 1,726) that evaluated olive leaf (OL) or olive pomace (OP) supplementation on 21 standardized cardiometabolic and anthropometric biomarkers. Trials were pooled using random-effects models and certainty of evidence was appraised with GRADE. Overall, the effects of OL/OP supplementation were generally modest and heterogeneous. Some trials and pooled estimates suggested small improvements in selected lipid parameters (for example, LDL cholesterol and triglycerides in subsets of studies), markers of glycemic control and insulin sensitivity (fasting glucose, insulin-related indices), markers of systemic inflammation (e.g., CRP), and anthropometric measures (body weight and BMI). However, effect sizes were typically small, between-study heterogeneity was often substantial, and the GRADE certainty for most outcomes ranged from low to moderate. Key limitations across the evidence base included short intervention durations, small sample sizes, variable extract preparations and dosages, inconsistent comparator conditions, and risk-of-bias concerns. The review concludes that while OL/OP polyphenol-rich preparations may support modest improvements in some cardiometabolic markers, current evidence is insufficiently consistent or certain to make firm recommendations. Larger, longer, and better‑standardized RCTs are needed to clarify efficacy, dose–response, populations most likely to benefit, and mechanisms of action.
Full Analysis
Design and scope: This review pooled 30 randomized controlled trials (n = 1,726) that tested olive leaf or olive pomace supplements against placebo or control on 21 predefined cardiometabolic and anthropometric biomarkers. Meta-analyses used random-effects models and evidence certainty was graded using GRADE domains (risk of bias, inconsistency, indirectness, imprecision, publication bias). Strengths of the synthesis include a focus on RCTs, standardized outcome selection across metabolic, inflammatory, lipid and anthropometric domains, and transparent GRADE appraisal. Main findings: Across outcomes, pooled effects were generally modest and heterogeneous. Several pooled estimates and individual trials suggested small favorable shifts in some lipid parameters (LDL-C and triglycerides in certain subgroups), glycemic markers (fasting glucose, insulin indices), inflammatory markers (CRP, to a lesser extent cytokines), and modest reductions in body weight or BMI. However, few outcomes reached high-certainty evidence; most were judged low-to-moderate certainty. Sources of uncertainty: Heterogeneity was driven by variable extract types (leaf vs pomace), differing extraction methods and standardization (oleuropein/hydroxytyrosol content), wide dose ranges, short trial durations (often weeks to a few months), and small sample sizes. Some trials lacked rigorous allocation concealment, blinding, or complete outcome reporting, increasing risk of bias and imprecision. Potential mechanisms: Polyphenols such as oleuropein and hydroxytyrosol have plausible antioxidant, anti-inflammatory and metabolic effects; modulation of lipid metabolism, glucose handling and gut microbiota are candidate pathways, but clinical mediation remains speculative. Implications and research needs: While OL/OP supplementation may support small improvements in selected cardiometabolic markers, evidence heterogeneity and limited certainty preclude strong recommendations. Future RCTs should use standardized extracts with known polyphenol content, adequate power, longer follow-up, prespecified clinical endpoints or validated surrogate markers, and exploration of dose–response and mechanistic biomarkers including microbiome changes.Health Implications
Practical daily habits that align with the evidence: emphasize whole-food patterns rich in polyphenols rather than relying on a single supplement. Favor a Mediterranean-style diet with extra-virgin olive oil, olives, fruits, vegetables, legumes, whole grains and nuts. These choices may support cardiometabolic health alongside regular physical activity, adequate sleep, smoking avoidance, and limiting processed foods, added sugars and excess sodium. If considering olive leaf or pomace supplements, discuss with a healthcare provider—especially if you take medications—as preparations vary in potency and long-term impacts are not established. Focus on weight management and blood‑pressure friendly habits, which have the largest proven health effects.
Key Findings
- Pooled analysis of 30 RCTs (n=1,726) assessed 21 cardiometabolic and anthropometric biomarkers for OL/OP supplementation using random-effects models and GRADE.
- The review found generally modest and heterogeneous effects across outcomes — some lipid, glycemic, inflammatory, and anthropometric markers showed small improvements, but effect sizes, heterogeneity, and certainty varied, limiting confidence in firm conclusions.