Role of Intestinal Flora on the Metabolism, Absorption, and Biological Activity of Dietary Flavonoids

Abstract

Much attention has been focused on flavonoids because of their beneficial effects on human health. Flavonoids are the most abundant dietary polyphenols. Quercetin is one of the major flavonoids and is contained in many foods. Soybean and soy foods are rich sources of isoflavones. Recent research has shown that they are beneficial to human health. The two major sites of flavonoid metabolism are the liver and the intestinal flora. Intestinal flora play an important role in the absorption and metabolism of flavonoids. Many of the flavonols including quercetin occur in food in the form of Oglycosides, with D-glucose as the most common sugar residue. With respect to the bioavailability of flavonoid glycosides, intestinal flora are known to have an important role in hydrolysis. Colonic flora are known to catalyze the breakdown of flavonoids. It was also found that suppressing the breakdown of quercetin by intestinal flora is important for achieving higher concentrations of quercetin in the plasma. Soy isoflavone aglycone is absorbed faster and in higher amounts than glucosides in humans. Some dietary components are also known to affect the absorption of isoflavones. Human metabolism and excretion of isoflavones following the consumption of soy products show considerable variation. The bioavailability of soybean isoflavones to women is dependant on gut microflora. Equol is a metabolite of daidzein produced by intestinal flora. Equol has many biological activities relates to human health, and its production might be affected by dietary composition and intestinal floral composition. To achieve higher production of equol from daidzein in the gut, control of the metabolic activity of intestinal flora might be of importance.