Interest in the anti-cancer effects of soy spans more than two decades. Most of the attention has focused on potential protective effects of soy against breast cancer, due in part to the low rates of breast cancer in countries like Japan, where soyfoods are a regular part of the menu. More recently, though, research has put the spotlight on a possible role for soyfoods in reducing risk of endometrial cancer.
Cancer of the endometrium—which forms the inner lining of the uterus—is the fourth most common cancer in US women. In 2011, more than 46,000 cases were identified in the United States. Rates vary markedly throughout the world, though, suggesting that lifestyle plays a bigger role than genetics in risk for this cancer. One established risk factor is estrogen exposure. That’s why, unless a woman has had a hysterectomy and isn’t at risk for endometrial cancer, estrogen therapy combines estrogen with progesterone. Progesterone inhibits the harmful effects of estrogen on the uterus.
Since the isoflavones in soyfoods are related to estrogen, questions have been raised about their potential effects on endometrial cancer risk. To investigate those effects, researchers from the University of Hawaii Cancer Center analyzed the diets of 46,027 postmenopausal women living in Hawaii and compared them to the incidence of endometrial cancer. The women were enrolled into the study between 1993 and 1996 and at that time provided detailed information on their diets and other endometrial cancer risk factors. Over 13.6 years 489 women were diagnosed with endometrial cancer.
Women in the group consuming the highest amounts of isoflavones were about one-third less likely to develop endometrial cancer in comparison to women whose diets were low in soyfoods and therefore low in isoflavones. The results showed that the amount of isoflavones associated with protective effects is provided by about one serving of a traditional soyfood—one cup of soymilk, 1/2 cup of tofu or 1/4 cup of soynuts. Based on these findings, even small amounts of soyfoods could reduce risk for developing endometrial cancer.
Ollberding et al., Journal of the National Cancer Institute. 2011.