Flavanols, specifically flavan-3-ols, represent a major subclass of flavonoids featuring a 2-phenyl-3,4-dihydro-2H-chromen-3-ol backbone. These polyphenolic compounds occur naturally in cocoa beans, green tea, red wine, apples, and berries. They function as powerful antioxidants by scavenging reactive oxygen species and chelating metal ions. Epidemiological and clinical studies link dietary flavanol intake to improved vascular function, reduced LDL oxidation, lowered blood pressure, and potential neuroprotective effects. Procyanidins, oligomeric forms, contribute to astringency in foods. Bioavailability varies with polymerization degree and food matrix; monomers like (-)-epicatechin are absorbed in the small intestine while larger oligomers reach the colon for microbial metabolism. They are generally recognized as safe (GRAS) when consumed from food sources.