BACKGROUND Dietary phytoestrogens are ligands for the estrogen receptor and may mimic estrogenic effects in vivo. OBJECTIVE To assess the biological activity of isoflavone phytoestrogens, we analyzed the effect of dietary soy isoflavone supplementation on in vivo bioassays of estrogenicity. DESIGN Fifty healthy postmenopausal women aged 50-75 y participated in a double-blind, placebo-contro...