Phytoestrogens are plant derived compounds with binding affinity for the estrogen receptor and consequently have estrogen like activity. Phytoestrogens are found predominantly in eastern or soy-based diet compared to normal western diet. These compounds have manifold physiological effects in humans and their potency depends upon their ability to interact with estrogen receptors, ER-a and ER-b. In this review, (i) the structural relationships between phytoestrogens and physiological estrogens, and presence of phytoestrogens in our diet; (ii) proposed mechanisms of action of phytoestrogens; (iii) beneficial as well as detrimental effects of phytoestrogens; and (iv) present status of research to evaluate phytoestrogens in the prevention and treatment of different types of cancers and other diseases are examined. Exploring our floral diversity would be helpful in finding plants with potential estrogenic activity, which in turn could be used in the treatment of various ailments afflicting women.

Historically, many plants with potential estrogenic activity have been widely used in the treatment of ailments peculiar to women in folk medicine. Pomegranate is associated with fertility (Price and Fenwick, 1985), whereas hops were used by German clergy in the middle ages to lower fertility (Fuhrmann, 1986). Phytoestrogens, a term coined to describe plant derived chemicals that exert estrogenic activity, include a vast variety of structurally diverse compounds. The concept of phytoestrogens came to the fore when Allen Doisy published bioassay for estrogen (Allen and Doisy, 1923). Phytoestrogens gained importance in the 1940s due to infertility in sheep grazing on pastures rich in clover in Western Australia, later known as `clover disease' (Bennetts et al., 1946). By 1975, hundreds of plants were reported to have estrogenic activity. Based on epidemiological studies, Adlercreutz (1990) suggested that the reason for the reduced risk of diseases such as breast and prostate cancer and cardiovascular diseases in Asiatic and Mediterranean nations compared to Western countries could be attributed to their diet rich in phytoestrogens. Many industrially manufactured chemicals show weak estrogenic activity and are classified as xenoestrogens. These include organo chlorine pesticides, poly chlorinated biphenyls (PCBs), phenolic compounds and phthalate esters. Lack of biodegradability is a matter of major concern regarding xenoestrogens (Davis et al., 1993).

Phytoestrogens are naturally occurring non-steroidal plant compounds with structural similarity to principal mammalian estrogen 17 b-estradiol and have proven the ability to bind estrogen receptors in humans (Sirtori et al., 2005). They are widely seen in most plants, fruits and vegetables. Due to their structural similarity to human estrogen, they can bind both types of estrogen receptors a and b (Le Bail et al., 2000). Many phytoestrogens show higher affinity to the ER-b receptors, suggesting that they may mediate their actions through distinctly different pathways (Setchell, 1998). Phytoestrogens are much weaker than mammalian estrogen, with 10^_2 to 10^_5 times less activity (Price and Fenwick, 1985). Their activity primarily depends upon the amount of circulating endogenous estrogen and the number and type of estrogen receptors whether ER-a or ER-b (Cassidy et al., 1994). They are frequently present in the body in much higher concentrations than endogenous estrogens, rendering it more or less effective as endogenous oestrogen even though with less estrogenic activity (Adlercreutz et al., 1993).

Biotechnology Journal, phytoestrogens, Estrogen Receptors, ER, potential estrogenic, lower fertility, exert estrogenic activity, bioassay for estrogen, infertility in sheep grazing, breast and prostate cancer, cardiovascular diseases in Asiatic, estrogenic activity, xenoestrogens, organo chlorine pesticides, poly chlorinated biphenyls, PCBs, phenolic compounds, phthalate esters, biodegradability, non-steroidal plant compounds