Polyphenol combinations improve quercetin absorption and inhibit carbohydrate digestion while reducing glucose...

High saccharide intake contributes to the development of obesity and type 2 diabetes. Polyphenols such as quercetin, kaempferol, and isoquercetin have been shown to reduce carbohydrate digestion and monosaccharide uptake. This study examined their individual and combined effects on α-amylase and α-glucosidase activity using spectrophotometry-based assays as well as on glucose and fructose transport and polyphenol absorption in differentiated Caco-2 cells. Quercetin (200 μM) significantly inhibited α-glucosidase activity by ∼94%, while ∼10% inhibition of α-amylase activity was observed. A three-polyphenol mixture (equimolar 1 : 1 : 1 quercetin : kaempferol : isoquercetin) significantly inhibited α-amylase by ∼30%. Quercetin and kaempferol (100 μM) significiantly reduced glucose absorption by ∼50% and ∼25%, respectively. A mixture of all polyphenols (100 μM) significantly reduced glucose absorption by ∼57%. None of the tested polyphenols altered fructose absorption compared to the control. The mixture doubled quercetin absorption compared to quercetin alone at equal doses, which could be explained by kaempferol's inhibition of efflux transporters. These findings suggest that multi-component polyphenol formulations can enhance α-amylase inhibition and quercetin bioavailability while maintaining strong α-glucosidase inhibition.