flavanoles

Flavanols, also known as flavan-3-ols, are a subclass of flavonoids characterized by a saturated bond between carbon 2 and 3 and a hydroxyl group at carbon 3. They include monomeric units such as catechin and epicatechin and their polymers, known as proanthocyanidins or condensed tannins. Flavanols occur in both free and bound forms in various plant tissues.

In foods, flavanols are most abundant in cocoa and dark chocolate, tea (especially green tea), apples, grapes, berries, and some nuts. The monomer units can polymerize to form proanthocyanidins, which contribute to the astringency and color of fruits, wines, and other plant-derived products. The proportion of monomers, oligomers, and polymers varies with source and processing.

Bioavailability and metabolism of flavanols are variable. Monomeric catechin and epicatechin can be absorbed in the small intestine and enter systemic circulation in conjugated forms. Larger polymers, such as proanthocyanidins, are less readily absorbed in the upper gut and are metabolized by the colonic microbiota into smaller phenolic compounds that may be absorbed and later excreted in urine.

Health effects associated with flavanols have been investigated extensively. They possess antioxidant properties in vitro, and epidemiological studies link flavanol-rich diets with cardiovascular benefits. Randomized trials report modest improvements in endothelial function and blood pressure under certain conditions, but findings are inconsistent and dependent on dose, food matrix, and individual factors.

Safety considerations indicate that flavanols are generally safe as part of a balanced diet. Very high supplemental intakes can cause gastrointestinal discomfort or interact with medications; the long-term safety of concentrated extracts requires further study.