My wife developed breast cancer two years ago. After a mastectomy and chemotherapy she has done well. Because the cancer was estrogen-sensitive, the doctor is adamant about avoiding soy. The estrogenic compounds can attach to estrogen-secreting tissue. It's what makes soy good for peri-menopausal women. But with the fear of stimulating more cancer to grow, soy is a no-no.

I thought soy is soy, no matter what form you get it. But I'm not an expert. It's the only vegetable protein source that has all eight essential amino acids.