many nutritionists cite the Shanghai Women's Health Study when defending soy as part of a healthy vegetable based diet

https://pmc.ncbi.nlm.nih.gov/articles/PMC2683002/

It was a prospective cohort studies on diet and chronic disease in Asian women. Launched in 1996-2000, it enrolled approximately 75,000 Chinese women aged 40-70 and has tracked them for decades through follow-up surveys and health record linkage.

It cites lower breast cancer risk with soy consumption and attempts to explain that Isoflavones (genistein and daidzein), which are phytoestrogens  may modulate estrogen metabolism and have anti-proliferative effects on breast tissue....

but the study really demonstrates that fermented soy products (Miso, Fermented Tofu, Tempeh)
not soy supplements like soy protein may be good in a traditional eastern diet 

Unfermented Soy (Tofu, Soy Milk, Soy Powders) are  highly processed soy protein isolates or  that  lack the fermentation byproducts found in whole or fermented soy foods and deliver  doses of isoflavones  2-3 times what you'd get from equivalent protein in tofu or tempeh