Past research linking soy, an exclusive dietary source of a plant-derived estrogen known as isoflavones, to endometrial cancer has been inconsistent, requiring further exploration into this possibility. A recent study published in BJOG: An International Journal of Obstetrics and Gynaecology has revealed that women who eat food containing soy do not increase their risk of developing endometrial cancer.

"Our study found that intake of soy and isoflavones were not associated with the risk of endometrial cancer,” said Dr. Motoki Iwasaki, Epidemiology Division, Epidemiology and Prevention Group, Research Center for Cancer Prevention and Screening, National Cancer Center in Tokyo, in a statement. “Although the incidence of endometrial cancer is much lower in Asian countries, the incidence rate has been increasing. We also know that the consumption of soy foods among Japanese people is very high. We need further studies with a greater number of cases to verify these findings and add to the research base."

The research team led by Iwasaki issued two surveys to 49,121 women between the ages of 45 and 74 over the course of five years. Participants answered a questionnaire regarding lifestyle, demographic factors, and medical history in addition to a food frequency survey at the beginning of the study and a follow-up survey five years later. The food frequency survey focused on eight soy food items, including miso soup, tofu, and soymilk. Researchers also tracked the total dietary intake of two different types of isoflavones: genistein and daidzein.

At the five year follow-up questionnaire, 112 women were diagnosed with endometrial cancer. After adjusting for factors such as age, alcohol consumption, smoking, BMI, menopausal status, coffee intake, and number of deliveries, the research team found no link between high consumption of soy foods or isoflavones and an increased risk of endometrial cancer. Women who did report a higher consumption of isoflavones were older, nonsmokers, regular coffee and alcohol drinkers, had higher dietary intake of fruits and vegetables, and were more likely to have a history of diabetes.

"This large population-based study found no evidence of a protective association of soy food or isoflavone intake and previous studies have been inconsistent,” said BJOG Deputy-Editor-in-Chief John Thorp. “Confirmation of these results needs further investigation and larger more diverse studies."

According to the American Cancer Society, endometrial cancer, also known as uterine cancer, forms in the tissue lining of the uterus. An estimated 52,630 new cases of endometrial cancer are expected in the United States by the end of 2014, and 8,590 women will die as a result of their diagnosis. Women have around a one in 37 chance of developing endometrial cancer. Thanks to detection and treatment advancements, over 500,000 women have survived this type of cancer.

Source: Sawada N, Yamaji T, Iwasaki M, et al. Soy food and isoflavone intake and endometrial cancer risk: the Japan Public Health Center-based prospective study. BJOG. 2014.