There is a 30% lower risk of developing breast cancer among women in Asian countries who are known for their high soya intake (compared to American women). Also, there is a 21% reduction in mortality among women with breast cancer who consumed more soya.

It’s difficult to isolate soya’s benefits conclusively:

Isoflavone can act either like estrogen in the body, or it's opposite.

Soya’s benefits depend on the type of soya we eat. The isoflavone content is higher in unprocessed soybeans, compared to processed soya foods. 

Soya doesn't affect testosterone levels in men. A review of evidence found that regular soya food intake was associated with an almost 30% reduction in the risk of developing prostate cancer.

Some research has found that the benefits that soya provides are mostly determined by a woman's ability to produce equol, a bacteria that around 30% - 50% of adults produce in their intestines after eating soy.

Soya contains a high content of isoflavones that have estrogenic properties. It means they act like estrogen, the primary female sex hormone, and bind to estrogen receptors in the body.