I have been diagnosed with breast cancer that is estrogen-receptor positive (ER+). I hear conflicting recommendations about the safety of consuming soy at this point. I don't want to do anything that would increase my chance of recurrence or decrease the effectiveness of my cancer treatments (chemotherapy, radiation, Tamoxifen). Do you eat soy and why or why not?
This is a very short answer to your good question. You are correct that much information available to cancer survivors (and oncologists) is both confusing and conflicting. I have tried to sort through it all myself and come to some conclusions about what I will eat.
There are two questions that need answering:
The jury is still out on these questions about the consumption of soy for these patients, but there are very strong and consistent data showing Japanese women are not only diagnosed much less frequently with breast cancer but also, interestingly, if they do get breast cancer, they actually live considerably longer than women from westernized countries after a breast cancer diagnosis. There could be many reasons why that might be so, with intake of soy foods being only one possible reason. Those types of epidemiological research studies do not prove that soy is harmless, but I have seen no data showing that consumption of soy foods is related to increased cancer incidence or cancer recurrence.
My soy intake is comparable to the amount and type of foods that are common in Japan. I do not consume any soy pills or powders, which consist of only one or two of soy's compounds, like the phytoestrogen called genistein. There is actually one very good study in rats showing that the consumption of miso (soybean paste commonly consumed in Japan) actually greatly enhances the anti-cancer effects of Tamoxifen with ER+ breast cancer.
Some intriguing new research conducted in post-menopausal primates has shown that the highest dietary intake of soy isoflavones (i.e., phytoestrogens) had a beneficial or protective effect on various breast and uterine cancer risk markers when combined with a higher estrogen exposure similar to that found in an overweight, post-menopausal woman. (Dietary Soy Isoflavones Inhibit Estrogen Effects in the Post-menopausal Breast, CE Wood et al, Cancer Research 66:1241-1249, 2006)
However, a recently-held conference “Soy and Breast Cancer: Resolving the Controversy” concluded that definitive research was urgently needed to help guide clinicians and patients with safe dietary advice.
I have been consuming 1 - 3 servings of traditional soy foods (similar to a Japanese type and amount of soy food intake) since 1995 without a recurrence of my advanced and aggressive cancer during this time. There are many recipes on my web site to help you incorporate these foods into your diet.
There is not clear evidence for me to say that you should be eating soy foods to help combat your cancer at this time. Try to learn as much as you can about this issue. Ask your doctor and dietitian many questions, inquire about updates, and ask them to share references with you, so that you can make up your own mind about what is right for you.
I am not aware of any controversy regarding the consumption of soy foods by women with ER- breast tumors.
Thank you for writing me with your questions. I hope this brief explanation of my thought process and personal experience has been helpful to you.
faq posted 4/01, updated 1/05, updated 2/06
These questions and answers are intended to be of a general informative nature. Please consult with the Registered Dietitian in your cancer center or your health care provider for nutritional advice that can be individualized to your specific medical condition.
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