Phytoestrogens are secondary metabolites of plants displaying both estrogenic and antiestrogenic activity. Moreover, they can also act through other estrogen-independent mechanisms. Soya is their main source in human nutrition. Population-based studies have suggested that consumption of a phytoestrogen-rich diet protects from civilization diseases. The evaluation of their beneficial effects is rather confusing due to individual sensitivity of humans to biological effects of phytoestrogens.