Dietary isoflavones: Biological effects and relevance to human health

Substantial evidence indicates that diets high in plant-based foods may exp lain the epidemiologic variance of many hormone-dependent diseases that are a major cause of mortality and morbidity in Western populations. There is now an increased awareness that plants contain many phytoprotectants. Ligna ns and isoflavones represent two of the main classes of phytoestrogens of c urrent interest in clinical nutrition. Although ubiquitous in their occurre nce in the plant kingdom, these bioactive nonnutrients are found in particu larly high concentrations in flaxseeds and soybeans and have been found to have a wide range of hormonal and nonhormonal activities that serve to prov ide plausible mechanisms for the potential health benefits of diets rich in phytoestrogens. Data from animal and in vitro studies provide convincing e vidence for the potential of phytoestrogens in influencing hormone-dependen t states; although the clinical application of diets rich in these estrogen mimics is in its infancy, data from preliminary studies suggest beneficial effects of importance to health. This review focuses on the more recent st udies pertinent to this field and includes, where appropriate, the landmark and historical literature that has led to the exponential increase in inte rest in phytoestrogens from a clinical nutrition perspective.