Bioactive Isoflavones in Functional Foods: The Importance of Gut Microflora on Bioavailability

Abstract

Isoflavones present in soy may have risk and benefits to human health. Human gut microflora have been shown to exert metabolic activities on isoflavones, which influences bioavailability and bioactivity. Absorption of isoflavones is likely to occur in the small intestine where there is a diverse range of microfloral species able to hydrolyze conjugated isoflavones, releasing the bioactive aglycone for absorption or further metabolism and reconjugation. The identification of gut microbes that metabolize isoflavone aglycones is not well established. Such information may lead to a better understanding of the bioavailability of isoflavones in functional foods.

Genistein Regulated Serotonergic Activity in the Hippocampus of Ovariectomized Rats under Forced Swimming Stress

“…[21][22][23] Genistein is widely present in plants, including leguminous plants, mainly as many types of glucosides, and some as aglycone. 24) When genistein glucosides are consumed, they are first deglucosidated in the alimentary tract, and become genistein aglycone.…”

Dietary combination of soy with a probiotic or prebiotic food significantly reduces total and LDL cholesterol in mildly hypercholesterolaemic subjects

“…Of human gut microflora, lactobacilli and bifidobacteria are exclusively beneficial (Gibson, 1998) and thus termed 'probiotic bacteria ' (O'Sullivan, 2001). These bacteria have high b-glucosidase activity (Gibson, 1998;O'Sullivan, 2001;Turner et al, 2003), an enzyme necessary for the initial hydrolysis of the soy isoflavone glucosides and consequent absorption of the bioactive aglycones (Turner et al, 2003). These probiotic bacteria can be introduced to the gastrointestinal tract as live cultures contained in food matrices, such as yoghurt (Cummings et al, 1997) or alternatively, prebiotic dietary components can selectively stimulate the growth and/or activity of specific probiotic bacteria already resident in the gut (Gibson, 1999).…”

Mammalian lignans enterolactone and enterodiol, alone and in combination with the isoflavone genistein, do not promote the growth of MCF‐7 xenografts in ovariectomized athymic nude mice

“…8 Isoflavones are primarily found in soy products, which are the richest known dietary source. 9 Soy isoflavones, daidzin, glycitin, and genistin, are metabolized in the intestine to their aglycone forms, daidzein, glycitein, and genistein (GEN), respectively. 10 In experimental studies, feeding flaxseed, 11 the purified mammalian lignan precursors SDG 11 and hydroxymatairesinol, 12 or ENL 13 to rodents following administration of the mammary carcinogen 7,12-dimethylbenz[a]anthracene (DMBA), resulted in tumor growth inhibition, suggesting a protective effect of lignans or lignan-rich diets on breast cancer.…”