Soy Isoflavones and Breast Cancer

Introduction It has been recognized for several decades that the use of legumes in traditional eastern diets has played a significant role in the incidence and mortality of certain disease states. Soy beans and products containing soy possess unique phytochemicals known as isoflavones which are thought to exert many biological effects in the human body. Scientists have proposed that these unique isoflavones have hormonal influences which can interact with many different cell types producing varied physiological responses. Epidemiological data, human cell line studies, randomized trails and review articles have consistently shown that certain population groups (Asians, vegetarians) who regularly consume a soy-based diet are afforded protection from breast cancer, endometrial cancer, prostate cancer, heart disease, osteoporosis, and symptoms of hormonal deficiency. Typically, Japanese women have higher levels of circulating and urinary isoflavones compared to Western women with concomitant lower rates of hormone-dependent cancers. Japanese women also have lower rates of osteoporosis, heart disease and menopausal complaints. Researchers have postulated that soy isoflavones may act as weak estrogen antagonists by influencing estrogenic metabolism and menstrual cycle length in premenopausal women but may concurrently act as weak estrogen agonists in postmenopausal women. Breast cancer has been associated with higher circulating levels of estradiol and prolactin with lower levels of progesterone. The proposition, therefore, has been made that soy isoflavones may modulate breast cancer risk in menopausal women but may also afford protection to the bones, cardiovascular and