Soy & Breast Cancer Michelle Sulprizio Student Dietitian Community Servings Spring 2013

What is Soy?  A subtropical plant native to Southeastern Asia.  It contains protein, isoflavones and fiber.  Isoflavones are phytochemicals believed to affect hormonal signaling.

Common Sources of Soy  Processed soy foods (e.g., veggie burgers, meatless dinner entrees, chicken-free nuggets, soy "ice creams" and energy bars) are usually high in protein, and typically contain lower levels of isoflavones. Soy Beans Edamame Soybean flour Tempeh Tofu Miso Bean curd Soy milk Soy yogurt Soy ice cream Soy butter Soy cheese Soy noodles Soy hotdogs Soy Protein Powders

Estrogen & Breast Cancer  Some breast cancers are sensitive to your body's naturally occurring female hormones, estrogen and progesterone.  Estrogen receptor (ER) positive is a type of breast cancer is sensitive to estrogen.  Breast cells contain estrogen receptors, and when the "key" (estrogen) joins with the "lock" (the estrogen receptor), a series of signals are sent which can cause ER positive breast cancer tumors to grow.

Isoflavones  Compounds that in some ways mimic the action of estrogen under certain conditions.  Levels vary in different types of tofu and soy milk products.  Your body's estrogen is much, much stronger than the estrogen-like isoflavones in soy.

The Controversy  The relationship between soy and breast cancer has become controversial because of concerns that isoflavones may stimulate the growth of existing ER positive breast tumors.  On the other hand, if the weak soy substance replaces the natural high-strength estrogen in cells, then maybe the soy will protect against cancers that would prefer a stronger estrogen signal.

Soy & Breast Cancer Risk  Studies of healthy women in the U.S. have either shown no association between soy and breast cancer, or a protective association, meaning that people who ate more soy had less breast cancer.  Studies of Asian women have found a lower risk of breast cancer with eating more soy.

Soy & Breast Cancer Survivors  A recent study looked at soy consumption in the diets of more than 9,000 breast cancer survivors o Women from both the U.S. and China who consumed 10 mg/day or more of soy foods had a 25% lower risk of breast cancer recurrence.  3 oz. serving of tofu: 28 mg of soy  8 oz. of soy milk: 10 mg of soy  Soy burger: 50 mg of soy  Single soy bar: 60 mg of soy

Challenges with this Topic  Women in Asia eat about 10 times the quantity of soy foods as the average American in the U.S, yet East Asian women have lower rates of ER positive breast cancer than women in the U.S.  Evaluating the risk of breast cancer with high levels of soy consumption is difficult.

Guidelines  Current research finds no harmful effects to the general population or breast cancer survivors from moderate consumption of soy foods, 1-3 servings of soy a day (a serving is about ½ cup).  Recommend avoiding soy supplements as they contain much higher isoflavone concentrations than what you would normally find in foods. The 2012 American Cancer Society Guidelines on Nutrition and Physical Activity:

Food for Thought  Remember that breast cancer survivors (and the rest of the population) are also at risk for other cancers and cardiovascular disease.  Tofu and other soy foods are linked to lower rates of heart disease because they are excellent sources of protein, may replace other less healthy foods in the diet (e.g. animal fats, red and processed meats), and may help lower cholesterol.  If you are taking hormonal therapy to fight off ER positive breast cancer, and are concerned about any phytoestrogen effects, ask yours doctor or R.D. how much soy you can eat.

Sources       2/08/02/the-bottom-line-on-soy-and-breast-cancer-risk.aspx 2/08/02/the-bottom-line-on-soy-and-breast-cancer-risk.aspx  cancer-survivors.html cancer-survivors.html  and-soy-milk/ and-soy-milk/ 