World-wide statistics indicate that Japan enjoys a 75% decreased incidence of breast cancer and an 80% decreased incidence of prostate cancer compared to the United States, Canada and many other developed countries. Many epidemiological studies suggest that much of the variation in breast and prostate cancer incidence between Asian countries and modern Western countries may be explained by the higher consumption of soy foods and soy isoflavones, which are staples of the Japanese and Asian diets. A high ingestion of soy foods is also associated with lower cholesterol levels and a decreased incidence of cardiovascular disease. (1,2) In 1991, the US Food and Drug Administration awarded a health claim for the cholesterol-lowering properties of soy protein, concluding that 25 gm of soy protein was sufficient to lower serum cholesterol levels to a modest degree. (3)
In regards to the prevention and management of reproductive organ cancers soy isoflavones were first shown to have anti-estrogenic effects in rodents in 1966. Most recently, isoflavones have been shown to bind to beta-estrogen receptors. Some data indicates that when these receptors are activated by isoflavones, it inhibits the replication of estrogen-stimulated growth of breast cells and breast cancer cells. (3) Many other anti-cancer mechanisms for isoflavones have also been reported in the scientific literature. For example, soy isoflavones have been shown to lower estrogen levels, stimulate the production of sex hormone-binding globulin by the liver (which in turn leads to more estrogen-bound and less free estradiol, reducing the amount of estrogens available for binding with estrogen receptors). The result is less stimulation of reproductive tissue by estrogen, which is associated with a lower risk of breast and uterine cancer.
Soy isoflavones also inhibit the enzymes that promote cell replication (protein tyrosine kinase, DNA topoisomerase and ornithine decarboxylase), and inhibit angiogenesis (which prevents the building of life-supporting blood vessels in and around malignant tumors). Soy isoflavones also provide antioxidant defence and encourage cell maturation – all of these effects are associated with a lower risk of reproductive organ cancers. Further, the weak estrogenic potential (more than 1,000 times weaker than estradiol) of soy isoflavones does not elicit a strong estrogenic response and thus has an anti-estrogenic effect that tends to inhibit the growth and proliferation of estrogen-dependent cancer cells, as demonstrated by the research of A. Molteni et al. (5,6,7)
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