Soy Isoflavones and Health

DOERGE D R and SHEEHAN D M (2002) Goitrogenic and estrogenic activity of soy isoflavones. Environ Health Perspect. 110 (Suppl 3) 349-53. 

Reinwald, S. C.M. Weaver. Soy isoflavones and bone health A double-edged sword J. Nat. Prod. 2006, 69, 450-459. 

E. Ricci, S. Cipriani, F. Chiaffarino, M. Malvezzi, F. Parazzini (2010) Soy isoflavones and bone mineral density in peri menopausal and postmenopausal western women a systematic review and meta-analysis of randomized controlled trials. J. Womens Health, 19, 1609-1617. 

Ricci, E., Cipriani, S., Chiaffarino, F., Malvezzi, M., and Parazzini, F. 2010. Soy Isoflavones and Bone Mineral Density in Perimenopausal and Postmenopausal Western Women A Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Womens Health (Larchmt). 

SETCHELL K D (1998) Ph)doestrogens the biochemistry, physiology, and implications for hiunan health of soy isoflavones. Am J Clin Nutr. 68 1333-46. 

MESSINA M, GUGGER E T and ALEKEL D L (2001) Soy protein, soybean isoflavones, and bone health a review of the animal and human data. In Wildman REC, Handbook of Nutraceuticals and Functional Foods, Boca Raton, CRC Press EEC, 77-98. 

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). 

The Japanese diet differs in many aspects from its Western counterpart, not only in consumption of soy but also of fish. To date, however, soy alone appears to have attracted the attention of researchers. The structural similarity between the isoflavones contained in soy and estrogen has perhaps made it conceptually easier to associate soy consumption and the low incidence of hot flushes in Japanese women. This may prove to be too simplistic as it is highly likely that a combination of nutrients, rather than just one compound, may determine the favorable health effects of the diet. 

Interindividual variation in ability to metabolize daidzein to equol (more estrogenic and a more potent antioxidant than daidzein) could thus influence the potential health protective effects of soy isoflavones. The extent of gut microflora metabolism in humans is variable, approximately 35% of a Western population can produce equol. ... 

Although toxicity from isoflavones may arise from their action as alternative substrates for the enzyme thyroid peroxidase and people in southeast Asia would be protected by the dietary inclusion of iodine-rich seaweed products, a recent study has shown that isoflavone supplements do not affect thyroid function in iodine-replete postmenopausal women. Considerations of the safety of soy isoflavones is an area of great interest in relation to their potential benefits to human health and has recently been comprehensively reviewed. ... 

In 1999, the US FDA allowed health claims (on food labels) on the association between soy protein and reduced risk of coronary heart disease for foods containing >6.25 g of soy protein, assuming either four servings, or that a total of 25 g of soy protein are consumed daily. Furthermore, in 2002, the UK Joint Health Claims Initiative approved a health claim on the association between soy protein and cholesterol reduction, the inclusion of at least 25 g of soy protein per day, as part of a diet low in saturated fat, can help reduce blood cholesterol levels and it is important to note that this claim relates to soy protein that has retained its naturally occurring isoflavones. 

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