High intake of diets rich in isoflavones, such as miso soup, may decrease the risk of developing breast cancer.

This study investigated the relationship between the consumption of isoflavone-rich foods, such as miso soup, and the incidence of breast cancer in Japanese females. Using self-administered dietary questionnaires, researchers examined the isoflavone and soy food intakes of 21,852 Japanese women between the ages of 40 to 59 years. The breast cancer hazard ratio was also assessed in all the subjects.

Researchers found a low prevalence of breast cancer among subjects who regularly consumed large servings of isoflavone-containing foods, such as miso soup. This breast cancer protective effect of isoflavone was found to be stronger in postmenopausal women. Accord to this study, high intake of soy foods had little or no effect on breast cancer risk. The results of this study show that increased consumption of diets high in isoflavones may confer significant protection against the development of breast cancer in Japanese women.