Much of the early excitement about the potential role of soyfoods in reducing risk of breast cancer was based on the knowledge that soyfood-consuming countries such as China and Japan have had historically very low rates of this disease. However, as these countries have experienced Westernization of their cultures, including a change in diet, breast cancer rates have dramatically increased.
For example, since 2003, breast cancer has become the most common type of cancer among women in Taiwan and the fourth leading cause of female cancer deaths. In fact, the incidence of breast cancer has doubled within just two decades. The good news is that new research from Taiwan indicates that greater soyfood consumption could help stem this unwelcomed tide.
This suggestion comes from a study of 233 breast cancer patients and 236 women similar in age but without breast cancer. To determine dietary intake, each study participant filled out a questionnaire that included questions about the intake of 28 frequently-consumed food items. The women also indicated whether they were a vegetarian.
From the questionnaire, the researchers were able to identify 5 different dietary patterns: 1) high meat 2) high processed meat 3) high fruits and vegetables and soyfoods 4) high consumption of desserts and sugar and 5) high consumption of fermented food. The results indicated that the high meat and high processed meat dietary patterns were associated with an increased breast cancer risk. Conversely, a vegetarian diet was protective against breast cancer.
To determine the impact of soyfood intake on risk of breast cancer the investigators estimated the amount of isoflavones the women in this study consumed. Isoflavones, which are purported to be anti-cancer agents, are found in uniquely rich amounts in soyfoods. Women with breast cancer consumed significantly lower amounts of isoflavones than women without breast cancer. And most importantly, women who consumed more than 22 milligrams of isoflavones per day were 63% less likely to develop breast cancer in comparison to women who consumed fewer than 22 milligrams daily.
Twenty-two milligrams is the amount of isoflavones found in one serving of a traditional soyfood, such as one cup of soymilk or ½ cup of tofu or edamame. These results from Taiwan strongly indicate that consuming a more plant-based diet and as little as one serving of soy daily is protective against breast cancer.