Amultitude of substances are present in small amounts in plants that can affect mammalian biological processes relevant to cardiovascular disease and other common human diseases. 1 However, few of the thousands of bioactive molecules have been studied well in cells or animals, and still fewer in humans. This slim evidence base notwithstanding, a staggering array of these compounds are available for our use as pricey nutritional supplements. The phytoestrogens are arguably the most intensively studied of these substances, and as a result, conclusions about them can be drawn with good scientific support. Phytoestrogens are a subcategory of compounds called flavonoids, a group composed of hundreds or more types of molecules. The 2 classes of phytoestrogens are isoflavones, notably found in soy products, and lignans, present in nuts, fruits, cereal grains, tea, and coffee. 1–3 Because of their assumed health benefit, isoflavone content is advertised in many foods that contain soybeans, and isoflavones are sold as nutritional supplements.