A government-sponsored Japanese study showed that women who have high intake of soybeans pose reduced risk of developing breast cancer.
Women who had high levels of genistein, a compound found in soybeans, had less of a chance of developing breast cancer than women with less of it, said the study by the National Cancer Center in Tokyo.
Soybeans in Japan are eaten as tofu, miso soup or Japanese fermented beans known as "natto."
The study followed approximately 25,000 women aged between 40 and 69 throughout Japan for an average of 10 and a half years.
The team studied the relationship between genistein concentration and breast cancer risk by comparing blood samples taken from a 144 women who had developed breast cancer and 288 who did not.
The risk of cancer for those with the highest level of genistein was one-third of that for the group with the lowest concentration, the study said.
Women who had the highest concentration of genistein in their blood consumed 100 grammes (3.5 ounces) of tofu or 50 grammes (1.75 ounces) of "natto" per day, it said.
However, the study warned that excessive consumption of genistein and other isoflavone compounds -- especially in the form of supplements -- may actually raise the risks of breast cancer.
"These results were limited to daily consumption of isoflavone at meal times. So if the consumption occurs within meals, there should be no problem," said Motoki Iwasaki, a team member at the Epidemiology and Prevention Division.
Another recent study showed older women who eat soy-based foods faced lower risks of heart disease.
The study was published in the US-based Journal of Clinical Oncology.