Polyphenol consumption and endurance exercise performance: A systematic review and meta-analysis of randomised controlled trials

Abstract

Introduction: Consumption of polyphenols is proposed to reduce oxidative damage and increase nitric oxide synthesis and availability, thereby inducing physiological effects that enhance endurance exercise performance. Thus, the objective of this study was to systematically review the literature to evaluate the effects of consuming polyphenol-rich foods on endurance exercise performance. Methods: This study comprised a subanalysis of a larger systematic review. Electronic searches of Scopus, Web of Science, Ovid Medline, EMBASE and SportDiscus databases were performed. Studies were included if they involved consumption of foods containing polyphenols, and a measure of endurance exercise performance was reported. Risk of bias was assessed using the Cochrane RoB 2.0 and random effects meta-analysis was conducted, with subgroup analyses performed based on food type, sex, fitness level, and supplementation dosage and duration. Results: Data from 58 studies met eligibility criteria, with 55 studies included in the meta-analysis. Meta-analysis identified trivial but significant benefits for the overall consumption of polyphenol-rich foods on endurance exercise performance (SMD= 0.17, p<0.001). When evaluated by food type, grape, (nitrate-depleted) beetroot, French maritime pine, Montmorency cherry and pomegranate exhibited significant ergogenic effects, while no significant effects were evident for New Zealand blackcurrant, cocoa, ginseng, green tea or raisins. Significant positive effects were evident following both acute and multiple-day supplementation and meta-regression indicated that total polyphenols consumed did not moderate effect size. No effect of polyphenol consumption on exercise performance was found in females (SMD= 0.01, p=0.95), but small to moderate effects (SMD=0.21-0.76, p<0.001) were found in males across a range of fitness levels (V̇O2max 41-71 ml.kg.min-1). Limited evidence supported polyphenol-rich foods enhancing nitric oxide availability, improving vascular function, reducing oxidative damage or other physiological indicators that may explain these ergogenic benefits. Considerable heterogeneity in effect sizes of included studies was present, which may reflect variation in polyphenol bioavailability between foods, differences in study designs and subject characteristics. Discussion: Foods rich in polyphenols provide benefits for endurance exercise performance in males, but not females. These sex-specific benefits were observed across a range of fitness levels, from untrained to well-trained athletes. There is limited direct evidence of the mechanisms underpinning these effects. Other: The review protocol was registered on the Open Science Framework (https://osf.io/u7nsj). My co-authors and I acknowledge that we have no conflict of interest of relevance to the submission of this abstract.