The soy bean have compounds called isoflavones, which are a subclass of flavonoids and are called phytoestrogen compounds due to their structural similarity with human hormone estradiol. These soy isoflavones are made of 12 isomers 3 aglycons (diadzein, genistein, glycitien) and 9 glucosides (diadzin, genistin, 6'-0-acetysdiadzin, 6'-0-acetysgenistin and 6'-0-acetysglycitin, 6'-0-malonysdiadzin, 6'-0-malonylgenistin and 6'-0-malonylglycitin. These are know for their many chemical reactions, such as antioxidative properties, anticancer, antiestrogenic , estrogenic and apoptosis. Traditional non fermented soybean foods have greater levels of glycosides whereas greater levels of aglycans in fermented foods.
It is known that women living in Asia have lower risks of heart disease, breast cancer and meno-pausal symptoms than western women. These differences in risks, however, disappear with in a generation or two after Asian women emigrate to west. In recent years, researchers have attributed these differences in disease and symptoms risk to diet factors, particularly on phytoestrogens. It is reported that Phytoestrogens were weak estrogens that bind to estrogen receptors and exert hormonal and anti hormonal effects. Isoflavones is a class of Phytoestrogen that is present more in soybeans. Phytoestrogens were alternative to hormone replacement therapy (HRT) for peri- and post–menopausal women. Primary claims of it were reduced menopausal symptoms, improved cardiovascular, bone and breast health.
In women, menopausal hormonal changes leads to uncomfortable vasomotor and others physical and psychological symptoms, the most widely experienced vasomotor menopausal symptoms are hot flushes and night sweats. Estrogen is main effective treatment but women avoiding due to its side effects and increased cancer risk. 85% of women in North American had reported incidence of hot flushes.15-25 % of women in Asia had reported incidence of hot flushes. Soy protein does not appear to be required and the greatest benefit may be realized when the supplement is taken in divided doses throughout the day and in subjects with more severe symptoms. Unlike estrogen therapy, soy isoflavones do not appear to stimulate the endometrium and should therefore not increase risk of endometrial cancer, as does exogenous oestrogen
An average soy protein intake of 47 g/day compared with animal protein lead to significant average decrease of 9% to 13% respectively in concentration of total cholesterol and low density lipoprotein (LDL) cholesterol as well as small non-significant increase in high density lipoprotein HDL cholesterol epidemiological studies have suggested that changes of this magnitude could result in 25-50% decrease in cardiovascular disease risk. In order to determine whether isoflavones are responsible for soy’s lipid lowering effects, a few studies have compared the effects of an isoflavone-rich protien isolate with an isoflavone-depleted soy protein isolate. Results showed that isoflavone-rich isolate exerts greater effects than the isoflavone-poor isolate suggesting that isoflavones are required, the highest isoflavone dose resulted in beneficial effects on lipoprotein profiles with up to 10% decline for LDL cholesterol and 14% increase of HDL.
Comparative study performed on women living in Asia and us have shown increased bone mineral density (BMD) in women consuming greater quantities of isoflavones.
The epidemiological data supported an inverse association between phyto-estrogens and breast cancer risk.
Wang, H.J.; Murphy, P.A. Mass balance study of isoflavones during soybean processing. J.Agric.Food Chem. 1996, 44, 2377-2383.
Wang, H.; Murphy, P.A. Isoflavone content in commercial soybean foods. J.Agric.Food Chem. 1994, 42, 1666-1673.
Lee, C.H.; Yang, L.; Xu, J.Z.; Yeung, S.Y.V.; Huang,Y.; Chen, Z.Y. Relative antioxidant activity of soybean isoflavones and their glycosides. Food Chem. 2005, 90, 735-741.