There is controversy about the soy isoflavones, but the best information I have is that this a good substitute for HRT, with substantially less risk. The controversy is based upon the fact that soy isoflavones provide a weak estrogenic stimulation. This is their value. But in some very sensitive people, even weak stimulation has the potential to stimulate some cancer formation, though in most people it provides a protective effect.
To quote from a recent article in the peer reviewed “There is considerable epidemiological evidence, including a review of 21 studies on 26 different cancer sites, that soy isoflavones might provide protection from several types of cancer…Case-controlled, epidemiological , animal, and in vitro studies all point to the effectiveness of soy isoflavones for the prevention of breast cancer.”
There is recent concern that feeding soy to children may provide excessive estrogenic stimulation, but research studies have demonstrated that this is not the case. The best information on soy currently is that it is safe and effective both preventing estrogen-based cancers and in providing some of the bone-strengthening and other benefits associated with estrogens.