Soy Foods Reduce Uterine Cancer Risk

Endometrial cancer begins in the lining of the uterus, called the endometrium. It is the fourth most common cancer in women, occurring mostly between 50 and 70 years of age. Estrogen and progesterone are steroid hormones that exist in a delicate balance in the body. When too much estrogen is present relative to the amount of progesterone, cells in the endometrium begin to divide more rapidly. This increases the risk of developing endometrial cancer.

Some factors that contribute to excess estrogen are menstrual periods beginning before age 12 and menopause after age 50, obesity (as estrogen is stored in fat tissue), diabetes, estrogen-replacement therapy (when taken without progesterone, estrogen is “unopposed” leading to a higher risk of cancer), never having been pregnant (progesterone increases during pregnancy, offsetting the negative effects of estrogen on the uterus), and irregular ovulation. Other factors that may increase the risk of endometrial cancer are a family history of colon or endometrial cancer, a personal history of breast or ovarian cancer, and taking the drug tamoxifen for breast cancer. Shifting the balance between estrogen and progesterone in the body may decrease the chance of developing endometrial cancer. Women who take oral contraceptive pills for a number of years have a lower risk of endometrial cancer. Maintaining a healthy weight can also decrease the risk.

Soy foods contain phytoestrogens, or plant estrogens, such as the isoflavones daidzein and genistein. Phytoestrogens can act as weak estrogens and also have anti-estrogen activity. They can decrease the amount or the effect of estrogen in the body by binding to estrogen receptors and blocking other (harmful) estrogens from binding, inhibiting the production of certain forms of steroid hormones that are linked to cancer development, and increasing the clearance of steroids from the body. Asian women who eat more soy foods than women in western countries have a lower rate of endometrial cancer.

The new study investigated the intake of soy foods and the risk of endometrial cancer among women living in China. The study included 832 women with endometrial cancer and 846 healthy women of similar age (control group). The participants answered a detailed questionnaire assessing risk factors for endometrial cancer and usual dietary intake for the previous five years, including the type, frequency, and amount of soy foods eaten. Participants’ height, weight, and waist and hip measurements were recorded.

Women with endometrial cancer tended to eat less soy foods than did women in the control group. Endometrial cancer risk was significantly lower among women who ate soy foods regularly than among those who did not. The inverse relationship between soy intake and decreased cancer risk was most pronounced in overweight women, supporting the theory that soy has an anti-estrogen effect in women who have excessive estrogen levels.

The rate of endometrial cancer among Asian women living in Asia is one-third to one-fifth of that among women in western countries. This study confirms the association between increased soy intake and lowered risk of developing endometrial cancer.

Kimberly Beauchamp, ND, received her bachelor’s degree from the University of Rhode Island and her Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. She is a co-founder and practicing physician at South County Naturopaths, Inc., in Wakefield, RI. Dr. Beauchamp teaches holistic medicine classes and provides consultations focusing on detoxification and whole-foods nutrition.

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