The World's Healthiest Foods

Diet High in Soy Foods Lowers Breast Cancer Risk

A study published in the September 2002 issue of the American Association for Cancer Research (AACR) journal, Cancer Epidemiology, Biomarkers & Prevention, adds to growing evidence that consuming tofu and other soy-foods significantly lowers levels of a type of estrogen normally associated with breast cancer risk in postmenopausal women.

The study found a link between soy-rich diets consumed by Asian women in Singapore and reduced levels of estrone, the predominant form of estrogen in women after menopause. In postmenopausal women, higher levels of estrone have been linked to increased risk for breast cancer. In this study, researchers found that estrone levels were about 15% lower in women who consumed the most soy protein. No other modifiable lifestyle factors analyzed by the scientists yielded such a dramatic reduction in estrogen levels.

Practical Tips

The variety of soy foods now available in U.S. supermarkets makes adding this cancer-protective member of the World’s Healthiest Foods to your healthy way of eating simply a matter of choosing which products strike your fancy. In addition to a wide variety of baked and flavored tofu and tempeh choices, you can find soy burgers, soy hot dogs, soy milk and yogurt, soy nuts, and even soy ice cream.

Here are just a few of the World’s Healthiest Foods quick serving ideas to help you garner soy’s protective benefits:

  • Sprinkle roasted soynuts on top of green and grain salads.
  • Frozen soybeans (called edamame) are easy to prepare and make a great snack or addition to soups, stir fries or bean salads. Just add the edamame to lightly salted water and boil for approximately 10-15 minutes.
  • Use soymilk in place of cow’s milk as a beverage and cereal topper. Vanilla soymilk makes an especially delicious latté or cappuccino.

To learn more about the numerous health benefits of soy foods, truly some of the World’s Healthiest Foods, just click soybeans.

For some exceptionally fast, yet delicious recipes that will help you enjoy making soy foods a staple in your healthy way of eating, take a look at the World's Healthiest Foods' Recipes containing soy foods. Simply, click on the Recipe Assistant, select soybeans from the Healthy Foods List, and click on the Submit button. A list containing links to all our recipes containing soybeans will appear immediately below.

Research Summary

The participants in this study were 144 healthy postmenopausal Chinese women in Singapore who were enrolled in a population-based prospective investigation of the effects of diet on cancer risk. Information on diet and other lifestyle factors was gathered from a structured questionnaire given as part of direct interviews.

Each of the women, who ranged in age from 50-74 years, was asked to estimate her usual eating frequencies and portion sizes for 165 foods and beverages consumed during a year. Information was also obtained on demographics, lifetime use of tobacco, menstrual and reproductive history, medical history, and family history of cancer.

The Chinese population in Singapore (and elsewhere in Asia) is especially well suited for studies on the effects of soy-based foods since soy is a staple in the traditional Asian diet. In addition to soymilk, the questionnaire included six kinds of soy products (plain tofu, taupok, taukwa, foopei, foojook and tofu far).

Levels of the isoflavones daidzein, genistein and glycitein were measured in the main types of soy foods consumed in Singapore, enabling the researchers to also estimate the individual subject’s intake of isoflavones. Isoflavones, the primary active phytochemicals in soybeans, are believed to be responsible for the anti-cancer effects that have been observed in a growing number of human and animal studies.

“Results from this study support the hypothesis that high soy intake may reduce the risk of breast cancer by lowering endogenous (internally produced) estrogen levels, particularly estrone,” said Anna H. Wu, the study’s lead investigator and professor of preventive medicine at Keck School of Medicine of the University of Southern California, Los Angeles, CA.

Blood sample analyses showed lower estrone levels among those women consuming the most soy protein and also showed a similar lowering of estrone levels when correlated with the amount of isoflavones consumed. Estrone levels did not, however, decline in a linear fashion as soy intake increased; an apparent reduction in estrone was found only among those women in the top 25% of soy foods consumers.

No other dietary or lifestyle choices were found to affect hormone levels. These included consumption of alcohol, coffee, tea, fat, fiber and various micronutrients including vitamins A, C and E, calcium and carotenoids. Nor did physical activity significantly influence serum hormone levels.

The study also found an association between increased estrogen levels and a high body mass index (BMI), a measure of weight that takes height into account. “There is a suggestion that weight change (particularly weight increase) has a profound influence on breast cancer rates in Asian-American women,” said Hin-Peng Lee, co-principal investigator in the Singapore Chinese Health Study. “The same may now be happening to their relatives on the Asian side of the Pacific.”

This study may open new avenues of research to discover how soy foods work to reduce estrone levels on the molecular level. The scientific team has hypothesized that isoflavones may inhibit certain enzymes responsible for estrogen production and metabolism. “Our findings of a reduction of estrone levels in association with soy intake may represent a reduction in the production and/or an increase in the elimination of estrone,” said Dr. Stanczyk. “Future studies may offer new insights into this mechanism.”

“However, the effect of soy on the breast is controversial,” said Dr. Wu. “There are some in vitro studies of breast cancer cells – animal studies, as well as short-term soy intervention studies in women – suggesting that soy isoflavones may have stimulatory effects.”

“Aside from answering some basic questions about soy consumption and breast cancer, this study may provide some insight into the underlying increase in breast cancer in Asia,” said Dr. Stanczyk, a co-investigator and professor of research in obstetrics/gynecology at the Keck School of Medicine at USC. Historically, breast cancer rates among Asian women in Japan and China have been significantly lower than their Western counterparts. Until recently, low-risk Asian women had one-sixth the breast cancer incidence of high-risk whites in the United States and other parts of the West. Although the reasons for this difference are not fully known, it’s not due to genetics. Asian-American women have roughly the same breast cancer incidence as their Caucasian American neighbors.

Moreover, from the 1970s to the 1990s, breast cancer incidence more than doubled in Singapore and Japan. Reseachers theorize that earlier age at the onset of menstruation, increasing numbers of women without children and delay in childbearing may be part of the explanation, but also believe other changes in lifestyle play a role. One such change may be a movement away from the traditional soy-rich diet to one which contains lesser amounts of this beneficial food.

Reference: Wu AH, Stanczyk FZ, Seow A, Lee HP, Yu MC. Soy intake and other lifestyle determinants of serum estrogen levels among postmenopausal Chinese women in Singapore. Cancer Epidemiol Biomarkers Prev 2002 Sep;11(9):844-51

This page was updated on: 2002-10-08 03:39:17
© 2002 The George Mateljan Foundation