Phytoestrogens and breast cancer

Abstract

Phytoestrogens, which are widely distributed in plants, are structurally similar to mammalian estrogens and can thus bind weakly to estrogen receptors (1). The 3 major classes of phytoestrogens are isoflavones, which are concentrated in soybeans and soy products but are also found in other legumes; lignans, which are distributed in seeds, whole grains, berries, fruit, vegetables, and nuts; and coumestans, which are found in broccoli and sprouts. Although their medical importance has been less extensively studied, lignans occur in higher concentrations in US and European diets than do isoflavones. The daily dietary intake of phytoestrogens in white US women has been estimated to be <1 mg, with ≈80% from lignans, 20% from isoflavones, and <0.1% from coumestans (2).