The soybean and its many derivative products are staple foods in many Asian countries. In addition, it has long been one of the shining stars of the health-food scene. Although commonly used in tofu, soy can be found in many other forms, including meat and dairy analogues. Soy protein is available as a powdered product, and soy and its specialty compounds are offered in dietary supplements.
Soy contains valuable constituents, including protein, isoflavones, saponins and phytosterols. Research indicates some of these constituents may provide some very specific benefits, including cancer prevention, cholesterol reduction, building bone density, mitigating menopausal symptoms and fighting diabetes.
Soy & Cancer
Soy isoflavones have phytoestrogenic and antioxidant properties. The isoflavone genistein, and possibly daidzein, has been proposed to contribute an important part of soy’s anti-cancer effects. Genistein was tested in a study of human breast cancer cell lines, and was found to inhibit the growth of each of these cancer cells.1 It seems genistein affects estrogen receptors in such a way as to prevent breast cancer growth.2 This estrogen-altering response was also apparent in another study examining the influence of total soy isoflavones in premenopausal women, in which isoflavone consumption delayed menstruation and reduced cholesterol concentrations.3
Furthermore, soy’s anti-cancer effects are not limited to breast cancer. In vitro work in human and animal bladder cancer cell lines, using pure soy isoflavones (genistein, genistin, daidzein and biochanin A) and soy phytochemical concentrate, found both inhibited growth of the human and animal bladder cancer cell lines.4 Animal research also demonstrated the ability of genistein, soy phytochemical concentrate and soy protein isolate to inhibit the growth of bladder cancer in vivo, reducing tumor size by 40 percent, 48 percent and 37 percent, respectively, as compared with controls.
That said, there is some conflicting research about genistein and breast cancer. Some research suggests genistein is beneficial, while other research suggests it may actually contribute toward the disease.5 Much of the negative research has been primarily in vitro, while in vivo study results have been mixed. For example, in one study, genistein given to rats early in their lives helped reduce the incidence of mammary tumors; however, in research where mice were implanted with human breast cancer cells, genistein seemed to promote the growth of tumors in a similar way to estrogen (estrodiol).6