Friday, June 26, 2009

Soy, Breast Cancer and Tamoxifen?

Dear Monique, Hi there, I wonder if you could help me with some advice. I'm not expecting that you provide a total solution, or that any advice you give would be held against you. It's just I can't seem to find the answer or guidance anywhere, and I keep finding conflicting, vague views.

My history is that I was recently diagnosed with breast cancer (Stage 1) - I have had the tumor removed, and am presently undergoing radiotherapy. The cancer was seen to be estrogen receptive and I have been put on Tamoxifen for 5 years. I am nearly 43.

My readings suggest that increased soy intake is good for preventing breast cancer, but does it help after the fact? I have also read that taking high levels of soy can interfere with Tamoxifen. I've spoken to my oncologist -- but he seems very traditional and his feeling is that it can neither harm nor help?

Could you give me some advice, or point me in a direction where I can do further reading. Many thanks, Vicki

Answer: Dear Vicki, Thank you for contacting me with your concern about using soy while on Tamoxifen. I know there is a lot of confusing information regarding soy and breast cancer. The main reason for this is because healthcare professionals have established two different recommendations for women when it comes to soy consumption. One for women without breast cancer and one for women with, or at high risk for, breast cancer.

Women who do not have estrogen receptor positive breast tumors, and who do not have a strong family history of breast cancer, may eat all the soy they wish. For these women, the weak soy estrogen may actually protect against breast cancer by fitting into the receptor sites on breast tissue where estrogen usually attaches. Thus, preventing the more powerful human estrogen from attaching and starting the cancer causing process.

However, women with or at risk for estrogen stimulated cancers are cautioned to limit their intake of soy until researchers know for sure that plant estrogen will not stimulate their cancer to grow. Although plant estrogen is much weaker than human estrogen, there is a concern that any form of estrogen may stimulate tumor development in these women.

Additionally, women on Tamoxifen therapy are also urged to limit their consumption of soy-based products. Tamoxifen which is given to many breast cancer patients, is also similar to the soy isoflavone genistein. Both are able to combat tumors that contain estrogen receptors, both work on strogen-positive and negative cells, and both work by attaching to estrogen receptor sites. In order to get the most benefit from Tamoxifen, it is recommended that the intake of weak plant estrogen be restricted.

While there have been no studies to confirm these assumptions, until there is documented proof that phytoestrogens will not contribute to cancers, doctors will continue to be cautious and recommend restricting foods with these compounds. Again, this applies only to women who are in the risk groups mentioned above.

Since you are on Tamoxifen, I would suggest that you reduce your soy intake until you are off of it. I don't think you need to completely eliminate it from your diet. However, it is also wise to consult your own doctor about this if you are still unsure. Scientists are only beginning to understand the potentially powerful health benefits of soy. They are continually working to formulate what may be protective in soy, and what may not, realizing that not all cancers are the same.

For more information about Tamoxifen, go to

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Monique N. Gilbert, BSc. has offered guidance in health, nutrition, fitness and stress management since 1989. Through her writings, Monique motivates and teaches how to improve your well-being, vitality and longevity with balanced nutrition, physical activity and healthy stress-free living.

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