Frequently Asked Questions

Is there any new information for breast cancer patients who have ER+ tumors regarding the safety of eating soy foods?

The November 2001 issue of the Journal of Nutrition contains a lengthy article reviewing this very concern. It is entitled "Soy for Breast Cancer Survivors: A Critical Review of the Literature". The 2 authors, Mark Messina, PhD and Charles Loprinzi, MD examine this question in depth in the peer-reviewed article (Journal of Nutrition 131:3095S-3108S, 2001).

The article is an extensive review with 288 references. The historical perspective and background on both soy and isoflavones (particularly genistein, the phytoestrogen component of soy foods), along with in vitro, in vivo, and human data on the effect of soy and isoflavones on mammary tumor development, growth and metastasis are thoroughly reviewed by the two authors.

They also review information on soy and Tamoxifen. Two animal studies show significantly increased anti-cancer benefit from Tamoxifen when given with soy in the diet (these 2 studies are discussed in depth on my FAQ page at http://www.cancerrd.com/FAQs/FAQ30.htm). In addition, HRT for breast cancer survivors is discussed to compare with phytoestrogen data, including a recent epidemiological study that showed significant decreased risk of breast cancer recurrence and mortality among breast cancer survivors who took HRT versus those who did not. Of additional interest, other HRT observational data show the progesterone component in the HRT increases the risk of breast cancer more than the estrogen component.

Here are the concluding two paragraphs in the article:

"The available data, reviewed above indicate the lack of any convincing information to substantiate either of two extreme and opposing claims, each of which has been prominently and repeatedly put forth in both the lay and scientific literature. These two claims are as follows:
1.) Soy is protective against breast cancer and because of this should be recommended for consumption by healthy women and breast cancer patients
2.) Soy is harmful for women with a history of or at high risk for breast cancer and because of this should be avoided by such women.

The honest response to each of these diametrically opposed claims is that no convincing data exist to support either claim. In fact, there are strongly conflicting data regarding both. As such, if women (with or without breast cancer) enjoy partaking soy products, then it seems quite reasonable for them to partake of them. As with most things, moderation is intake is probably wise. In this regard, Asian soy intake may serve as a general guide for Western women."

Three references are cited in Dr. Messina's article to define what amount of soy comprises a typical Asian soy intake. Native Japanese adults typically consume ~30-40 mg (aglycone units) of isoflavones per day, which is roughly equivalent to between 1-1.5 servings (US measures) of traditional soy foods.

Mark Messina is a consultant to the soy industry but was one of the first health care professionals to publicly caution about the *soy will cure what ails ya* promotions in the media, particularly for breast cancer survivors and women at high risk for the development of breast cancer. He has consistently been very careful to base his stated views on the available science.

I have regularly been consuming 1-3 servings of soy foods per day since my diagnosis of breast cancer in 1995 without a recurrence of my ER+ breast cancer. I cannot say with any certainty that consuming soy has helped me remain cancer free during this time period, but I feel comfortable that it has been safe for me to consume during this time.

Diana Dyer, MS, RD

FAQ posted 02/02, updated 02/06

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Back to Main QandA Page Breast Cancer Is soy safe to consume for women with ER+ breast cancer? posted 4/01, updated 1/05 Is there any new information for breast cancer patients who have ER+ tumors regarding the safety of eating soy foods? posted 2/02 I am currently taking Tamoxifen. My daughter heard on TV that I should be eating soy to make it work more efficiently. Do you know of any studies verifying this information? posted 5/01, updated 1/05 I have read conflicting reports on the benefits vs. the dangers of Tamoxifen for breast cancer treatment. Have you found better nutritional alternatives? Should women with ER+ breast cancer avoid flaxseeds and flax oil that contain the phytoestrogens called lignans? Is weight gain common during breast cancer treatments? posted 8/00 What are some good breast cancer web sites? posted 4/04 Are there any foods I should avoid while taking Tamoxifen? posted 6/04 Does moderate alcohol consumption have a harmful effect on persons who have had breast cancer? posted 11/04 Should I be avoiding all caffeine to help fight my breast cancer? posted 11/04  Back to Main FAQ Page

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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.