(Journal of the National Cancer Institute) -- Frequent consumption of miso soup and high intake of isoflavones may be associated with a reduced risk of breast cancer, according to a new study. Isoflavones, which are abundant in soy, have been shown in laboratory studies to inhibit breast cancer, but it is unknown whether soy consumption is associated with a reduced risk of breast cancer in women.

Seiichiro Yamamoto, Ph.D., of the National Cancer Center Research Institute in Tokyo, and colleagues surveyed 21,852 Japanese women between the ages of 40 and 59 about their frequency of soy consumption. After 10 years, 179 of women had been diagnosed with breast cancer.

Women who drank three or more bowls of miso soup per day or consumed 25.3 mg/day of isoflavones (in the form of genistein) had approximately half the risk of breast cancer compared with women who had less than one bowl of miso soup per day or who consumed 6.9 mg/day of genistein. The observed benefit was greatest among postmenopausal women. The authors found no association between the consumption of soyfoods such as soybeans, tofu, deep-fried tofu, or fermented soybeans and the risk of breast cancer.