Answer by Dr Fernando, MD (oncologist) on Sat 29, Mar 2008 06:44pm:
Hi,
Before answering your question, I would just like to point out the misconception that breast cancer is caused by estrogen. Breast cancer, like other types of cancer, is caused by mutations in the genes that regulate the growth, maturation and multiplication of cells, resulting in a loss of control over these processes. Estrogen does not cause the mutation itself. This hormone stimulates the growth of breast tissue, whether normal or abnormal. Breast cancer cells, unlike normal cells, react to the stimulus provided by estrogen by growing in an uncontrolled fashion. While estrogen is responsible for the growth, the quality of this growth (whether controlled or uncontrolled) is due to the mutation of regulatory genes.
Back to your question: although soy products have been shown to contain estrogen-like substances called isoflavones, these have not been shown to have any physiologic effects similar to that produced by estrogen. In fact, a cross sectional study by Wu, et al (2002) on postmenopausal Singaporean women showed that 25% of the study population with the highest intake of soy products have 15% lower blood levels of estrogen compared to the rest of the study population.
So eating more soy products, at the very least, will not increase your risk of developing breast cancer. Wu's study even suggests that soy may have a protective effect, but additional research needs to be done to confirm this.
You can obtain a copy of the study using this link: http://cebp.aacrjournals.org/cgi/content/full/11/9/844
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