The Confusion Regarding Soy Products and Breast Cancer
I've been asked my opinion about this topic many times. And because I have several dear friends who are breast cancer survivors, I am intensely interested in any new information that might shed light on the consumption of soy foods and the risk of breast cancer recurrence.
Depending on who you talk to, you may hear that soy products are beneficial in reducing the risk of breast cancer or you may hear that soy products can have the opposite effect. I've always thought that soy should be beneficial. After all, according to the World Health Organization, in the U.S., where soy consumption is relatively low, 21.2 women per 100,000 have breast cancer. But in Japan, where the consumption of soy is much higher, the incidence is only 8.6 per 100,000 females.
Concern about eating soy foods comes from the fact that they are high in phytoestrogens which are chemically similar to the hormone estrogen. Estrogen is associated with breast cancer development so by connecting the dots one would easily come to the conclusion that soy might also increase the risk of this disease.
Results From a Recent Study
More than 5,000 women in China diagnosed with breast cancer participated in the Shanghai Breast Cancer Survival Study. It was found that women who ate in excess of 15 grams of soy protein a day had about a 30% lower risk of recurrence that those women who ate less than 5 grams per day. The most significant result of the study is that the benefits of soy foods were evident in both women with estrogen receptor positive and negative breast cancer. Most doctors presently tell women who have have estrogen receptor positive breast cancer to avoid soy products completely. This study may change that directive. The benefits of soy in reducing recurrence and death were also found in both women who used tamoxifen and those who did not.
Other Things to Note
Women in Asia generally consume soy in a very lightly processed form such as miso, soy beans, tofu and soy milk. They do not generally take soy supplements or eat highly processed soy found in fake meat products. They also consume soy foods throughout their life.
How Much Soy Protein is in Food
To find out how much soy protein is in food, check the label. If the food has an FDA-approved health claim on the label, it must contain a minimum of 6.25 grams of soy protein per serving. The FDA has approved the health claim that "25 grams of soy protein may help reduce the risk of heart disease".
For information on soybean nutrition, check out the National Soybean Research Laboratory. According to NSRL, the amounts of soy protein in commonly available foods are as follows:
* 1/2 cup (86 g) of cooked, mature (yellow) soybeans provides 14.3 grams of soy protein
* 1/2 cup (90 g) of edamame (green soybeans) provides 11.1 grams
* 1/2 cup (83 g) tempeh provides 15.8 grams
* 1/4 cup (43 g) soynuts provides 17.0 grams
* 1/2 cup (126 g) firm tofu provides 19.9 grams
* 1/4 cup (25 g) defatted soy flour provides 11.8 grams
* 1 cup (245 g) soymilk provides 7.0 grams
* 2 tablespoons (34.5 g) miso provides 4.1 grams
Talk to your Doctor
Although this study indicates that traditional soy foods may be both safe and protective against breast cancer reoccurrence, you should talk to your doctor about adding these products to your diet. To reference this study, See JAMA 2009 Dec 9;302(22);2437-43. Shu XO, Aheng Y, Cai H, et al. Soy food intake and breast cancer survival.