Most epidemiologic research indicates that higher soyfood intake is associated with a decreased risk of breast cancer. However, most of this research consists of case-control studies, a type of study design that carries less scientific weight than prospective studies. In prospective studies, researchers enroll healthy participants into the study and follow them for a period of years in order to determine whether those with particular lifestyle habits are more or less like to develop a particular disease. A just-published Japanese prospective study confirms that high soy intake is associated with a lower risk of breast cancer.
The more than 15,000 women who participated in this research were from Takayma, a city in a mountainous region of Japan. At study enrollment they were at least 35 years of age. The women were followed for a period of about 16 years, between 1992 and 2008. During this time, 172 cases of breast cancer were reported. Participants filled out a dietary questionnaire that assessed their usual intake of 169 food items, including a number of different soyfoods such as miso soup, deep-fried tofu, dried bean curd, soymilk and fermented soybeans.
At the end of the study, the women who had gone through menopause were divided into four groups according to the amount of soyfoods they consumed. Those who consumed the most soy – about 1½ servings per day – were almost 40% less likely to have developed breast cancer. Soy was not protective against premenopausal breast cancer. Interestingly, women who consumed as little as about ¾ serving of soyfoods per day derived as much protection against breast cancer as women consuming twice that much. This means adding just a little soy to the diet could significantly reduce a woman’s chances of developing breast cancer.
Wada et al. Int J Cancer. 2013.
