Dietary isoflavones bioavailability

Vergne, S., Sauvant, P., Lamothe, V., Chantre, P., Asselineau, J., Perez, P., Durand, M., Moore, N., and Bennetau-Pelissero, C. 2009. Influence of ethnic origin (Asian v. Caucasian) and background diet on the bioavailability of dietary isoflavones. BrJNutr 102, 1642-1653. 

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). 

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. 

The bioavailability of active thyroid hormones depends on the activity of deiodinases in thyroid follicular cells and in target tissues. In vitro experiments with purified enzyme revealed that some dietary flavonoids in micromolar concentrations inhibited thyroid type 1 iodothyronine deiodi-nase activity (Ferreira et al, 2002). Among the compounds tested was an isoflavone metabolite, biochanin A. So far, a few reports using various cell cultures (Mori et ai, 1996) or animals (cats) (White et ai, 2004) have confirmed that genistein at least is capable of inhibiting 5 -deiodinases. 

Fig. 78.1 Phenolics in human nutrition A microbiological perspective. Bioavailability of dietary compounds depends on the sum of molecular mechanisms underlying liberation of the compounds from dietary matrices, absorption, distribution into body tissues via blood circulation, metabolism (in the GI tract or target tissues), and elimination from the body. The keypad shows parameters of relevance to phenolic bioavailability. The two enlarged windows illustrate the diversity of both phenolics in food and microbial functions involved in phenolic conversion, with a focus on isoflavones and hgnans. Estimates of blood concentration of daidzein, equol, and enterolignans are...

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