Phytoestrogens are a group of plant-derived molecules (Figure 4.1) that are so named because they possess an estrogen-like activity. In 1949, adverse effects on fertility were observed in animals that had been grazing on phytoestrogenrich plants (Shutt, 1976). In the early 1980s it became clear that phytoestrogens could produce biological effects in humans, but it was not until the early 1990s that interest around these compounds really soared. What caused such a stir was the observation of a lower incidence of hot flushes in Japanese menopausal women compared with their Western counterparts (Lock, 1993). Japanese women also appeared to have a lower incidence of breast cancer, cardiovascular disease, and osteoporosis. In addition, Japanese men have a low incidence of prostate cancer. The low incidence of these conditions appeared

to be strictly correlated with the consumption of the traditional diet (Nagata et al., 2002).