Polyphenol-Rich Beverages Exert Beneficial but Variable Effects on Oxidative, and Inflammatory Markers in Metabolic Syndrome and Related Conditions: Evidence of Human Trials

Metabolic syndrome (MetS), one of the major global health concerns, represents a cluster of cardiometabolic risk factors along with chronic low-grade inflammation and oxidative stress as essential features. Lifestyle changes, including the health quality of the foods, are recommended as the initial interventions for the management and eventual reversal of metabolic syndrome. Considering the heterogeneity of the studies in evaluating the health benefits of polyphenol-rich foods, there is a lack of quantitative and even qualitative analysis of their potential impact on this pathophysiological condition. This review aimed to provide a coherent, clinically oriented appraisal of the potential role of polyphenol-rich juices and beverages in the management of metabolic syndrome and related cardio-metabolic conditions. Twenty-three human intervention studies, encompassing randomized controlled, crossover, and parallel-group designs, as well as non-randomized or uncontrolled intervention studies that prospectively evaluated a defined beverage. The collective evidence indicates polyphenols could improve anthropometric parameters and blood lipid levels, while data on insulin and blood pressure seemed inconsistent and limited. Regarding the antioxidant effects, most beverages beneficially affected lipid peroxidation and total antioxidant activity. Findings across the studies portray polyphenol-rich juices and beverages as consistent, though not uniformly potent, modulators of low-grade inflammation in cardiometabolic contexts. To draw any firm conclusions, future trials are recommended. These should adopt consistent polyphenol quantification and dosage applied, standardize analyzed parameters including inflammatory and oxidative stress panels, stratify participants by baseline status and medication use, and extend follow-up to evaluate reliability and clinical significance.