Recent data shows that children consume 40 milligrams of soy isoflavone per day with an adult consumption range of 150-200 milligrams per day. This study suggests that these levels are safe and effective. The research, funded by the US Department of Agriculture, found that about 25 percent fewer rats in a test sample had mammary tumors when fed a soy protein diet as compared to a standard diet. Soy is rich in isoflavones which sometimes block estrogen's bad effects, which is how the popular breast cancer drug tamoxifen works. Tamoxifen blocks estrogen's bad effects on the breast, while stimulating its good side-effects such as protecting bone density.
Tumors depend on new blood vessels to grow and spread.
Without blood vessels, cancer cells have no oxygen or nutrient supply. Researchers feel that this anti-angiogenesis property may contribute to soy protein's known benefits. Lower levels of the body's own estrogen are associated with a reduced risk of breast cancer. A number of independent studies on small groups of women have shown that women who drank soy milk had lower levels of estrogen in their blood. Dr. Lee-Jane W. Lu, of the University of Texas medical branch in Galveston, reported on her investigation of the effect of soy consumption on breast cancer.