(Poly)phenols: Mechanisms of action and efficacy of contemporary supplements for exercise recovery and performance.

(Poly)phenols are a diverse group of bioactive chemical compounds present in a wide range of plant- and animal-based foods. Several thousands of (poly)phenols exist; many have potent biological effects, most notably antioxidant, anti-inflammatory and vasodilatory. As such, they are of growing interest as nutritional interventions for health maintenance and disease prevention, but also for athletes aiming to enhance recovery and performance. Although most of their recovery and performance benefits are ascribed to their antioxidant actions, they are unlikely to function as antioxidants in vivo. Rather, they might upregulate the transcription factor nuclear factor-erythroid-2-related factor (Nrf2), which, by upregulating various endogenous antioxidants, could modulate cellular redox balance. Likewise, their anti-inflammatory functions are likely to be driven by their effects on the transcription factor nuclear factor kappa B, which regulates numerous pro-inflammatory genes. Although receiving far less attention, (poly)phenols might also increase mitochondrial biogenesis and fat oxidation, both of which could enhance endurance exercise performance. These biological effects have consistently been demonstrated in vitro, but there is less mechanistic support for them in human studies, despite several clinical trials reporting, albeit inconsistently, improved recovery and exercise performance. Translating the findings from in vitro and animal models to humans is challenging, in large part owing to the poor bioavailability of most (poly)phenols and thus the limited amount of the intact metabolites available for biological effects. This brief review outlines the primary mechanisms through which (poly)phenols might influence exercise recovery and performance and highlights some of the evidence from research that investigates popular (poly)phenol supplements on key performance and recovery outcomes.