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CRUCIFEROUS VEGETABLES, SOY & BREAST CANCER RISK

The role of soybean-derived isoflavones in cancer prevention is not entirely clear at this time.  However, there has been intense interest in tofu, and other soy-derived foods, as potential breast cancer prevention agents.  At the same time, because genistein, and other soy isoflavones, are known to variably act as both inhibitors and mimics of estrogen (the primary female sex hormone), cancer experts remain divided regarding the safety of regularly consuming soy isoflavones by women who are at an increased risk of developing breast cancer (chronic estrogen stimulation of the breast is a known risk factor for breast cancer).  Meanwhile, the high level of tofu consumption among women in the Far East, coupled with the much lower incidence of breast cancer in those countries when compared to the United States and other western countries, has fuelled speculation that tofu and other soy-derived foods may actually be associated with a reduced risk of breast cancer. 

In addition to soy isoflavones, there is also research data available suggesting that the frequent consumption of cruciferous vegetables, like broccoli and cauliflower, may also be associated with a decreased risk of at least some types of cancer, including breast cancer.

A newly published public health study from Singapore evaluated the impact of the regular intake of vegetables, fruit, and soy-derived foods on the risk of breast cancer within the large Chinese population in that country.  This enormous prospective epidemiological study, which began in 1993, and which appears in the current issue of the American Journal of Clinical Nutrition, included more than 34,000 women volunteers.  All of the 34,018 women in this study underwent detailed evaluation of their diets when they entered into this prospective public health study.  Among this very large group of women, 629 new cases of breast cancer were diagnosed during the course of this ongoing study. 

Based upon their self-reported dietary patterns, the women participating in this large epidemiological study were divided into two groups.  The first group consisted of women who regularly consumed cruciferous vegetables, fruit, and tofu.  The second group of women generally favored meat and starchy foods (such as dim sum), and consumed far fewer portions of vegetables, fruit, and tofu when compared to the first group.

The results of this study indicated that increasing levels of vegetable, fruit and tofu intake were associated with a significant decrease in breast cancer risk in postmenopausal women.   Among the women reporting the highest levels of intake of these foods, there was, on average, a 30 percent reduction in the risk of breast cancer when compared to the women who rarely ate these healthy foods.  Moreover, among the postmenopausal women who frequently consumed vegetables, fruit, and tofu, and who were observed for 5 or more years in this study, the apparent reduction in the risk of breast cancer grew even stronger, and these women were found to be 43 percent less likely to develop breast cancer when compared to women who rarely consumed vegetables, fruit, and tofu in their diets.

Therefore, in this large diet survey-based, prospective public health study,  a diet rich in vegetables (and cruciferous vegetables, such as broccoli and cauliflower, in particular), fruit, and tofu was strongly associated with a significant reduction in breast cancer risk in postmenopausal Chinese women living in Singapore.

Although there remains some concern that soy isoflavones may, under some conditions, actually stimulate the growth of either new or previous breast cancers (or cancers of the ovary or uterus), this public health study’s favorable findings are additive to a growing body of research data suggesting that both cruciferous vegetables and soy-derived isoflavones may be associated with a substantial decrease in the risk of breast cancer in women. 

To learn more about the potential role of cruciferous vegetables and soy isoflavones as part of a cancer prevention lifestyle, look for the publication of my new landmark evidence-based book, “A Cancer Prevention Guide for the Human Race,” in the summer of this year.

Dr. Wascher is an oncologic surgeon, a professor of surgery, a cancer researcher, an oncology consultant, and a widely published author

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