Isoflavones bioavailability

Larkin, TA. WE. Price L.B. Astheimer. Increased probiotic yogmt or resistant starch intake does not affect isoflavone bioavailability in subjects consuming a high soy diet. Nutrition 2007, 23, 709-718. 

XU X, HARRIS K s, WANG H J, MURPHY p A and HENDRicH s (1995) Bioavailability of soybean isoflavones depends upon gut microflora in women. J Nutr 125, 2307-15. 

The mucosa of the GIT represents an interface between the external and internal environments. The expansive surface area is necessary for the efficient hydrolysis of foodstuffs and the absorption of energy and nutrients. The mucosa also influences the systemic availability of non-nutrient compounds in the diet, both beneficial and detrimental. Digestion and absorption of glucosinolates are critical determinants of health benefits (see Chapter 4) Similarly, the bioavailability and health benefits of phytoestrogens, such as genistein (see Chapters 5 and 10) are at least partly dependent on the carrier-mediated processes of absorption associated with the GIT (Oitate et al, 2001). Moreover, the metabolic activities of the mucosa can influence the systemic concentrations and forms of dietary phytochemicals, as exemplified by research with soy isoflavones (Andlauer et al., 2000). 

Since 1999, when the Food and Drug Administration allowed the first health claim for soy-fortified foods in the USA, there has been a large increase in the sales of food products claiming to contain soy isoflavones. At the same time, over-the-counter supplements have become widely available. However, concerns have been raised about the real health benefits of such supplements in the absence of adequate information about bioavailability, pharmacokinetics and safety. To fill this gap, an extensive study on pure isoflavones and commercial soy isoflavone supplements has recently been carried out (Setchell et al, 2001). A selection of 31 commercially available supplements showed a wide variation in isoflavone composition and in the amount provided by one tablet. Furthermore, a lower isoflavone content, with respect to the claimed levels, has been observed in almost 50% of the analysed products. In one case, no isoflavones at all could be detected (Setchell et al, 2001). 

Such evidence indicates that it might be unnecessary to reach the same intake of soy products as Japanese or other Asian populations to reach the same plasma levels of isoflavones. The rationale for such a difference could be a different bioavailability of the ingested isoflavones. Indeed, in most Asians a deficiency of an intestinal lactase, responsible for P-glucosides hydrolysis, might explain the lower isoflavones concentrations in the blood of the Japanese (Day et ai, 2000). 

SETCHELL K D, BROWN N M, DESAI P, ZIMMER-NECHEMIAS L, WOLFE B E, BRASHEAR W T, KIRSCHNER A s, CASSIDY A and HEUBI J E (2001) Bioavailability of pure isoflavones in healthy humans and analysis of commercial soy isoflavones supplements. . 1 Nutr. 131 (4 Suppl) 1362S-1375S. 

Vergne S, Titier K, Bernard V, Asselineau J, Durand M, Lamothe V, Potier M, Perez P, Demotes-Mainard J, Chantre P, Moore N, Bennetau-Pelissero C and Sauvant P. 2007. Bioavailability and urinary excretion of isoflavones in humans effects of soy-based supplements formulation and equol production. J Pharm Biomed Anal 43(4) 1488-1494. 

K.D.R. Setchell, N.M. Brown, P. Desai, L. Zimmer-Nechemias B.E. Wolfe, W. T.Brashear, A. S. Kirschner, A. Cassidy and J. E. Heubi, Bioavailability of pure isoflavones in healthy humans and analysis of commercial soy isoflavone supplements. J. Nutr. 131 (2001) 13625-13755. 

Setchell, K.D., Brown, N.M., Zimmer-Nechemias, L., et al. (2002a). Evidence for lack of absorption of soy isoflavone glycosides in humans, supporting the crucial role of intestinal metabolism for bioavailability. Am. J. Clin. Nutr., 2, 447-53. 

The metabolism and bioavailability of isoflavonoids is likely to be of crucial importance to their ability to help protect human health against disease. Many studies have been published on the metabolism and bioavailability of isoflavones in adults. The metabolism of isoflavones is of particular interest because the potency of isoflavone metabolites differs from that of the parent compounds. The daidzein metabolite equol is three times as potent as is daidzein in an endometrial tumor line. Equol is also a more potent antioxidant in vitro (see Sections 7.3.5 and 7.4.2) ° and the clinical significance of the ability to form equol has been considered in depth. ... 

Setchell KDR, Brown NM, Deal PB et al. Bioavailability, disposition and dose-response effects of soy isoflavones when consumed by healthy women at physiologically typical dietary intakes. J. Nutr. 133, 1027-1035,2003. 

Intestinal microflora plays a key role in the metabolism and bioavailibility of isoflavones [86]. After ingestion, soybean isoflavones are hydrolyzed by intestinal glucosidases, which release the aglycones, daidzein and genistein, Fig. (16). 

The basis for understanding the health benefits of isoflavones requires detailed knowledge on the absorption, distribution, metabolism, elimination, and bioavailability of these phytoestrogens that demands robust, precise, accurate, and affordable analyses from biological and other matrices. 

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