The blog posting below from the same issue of AJCN reviews phytoestrogens generally. This is a great follow-up to the study that compares the two primary phtytoestrogens, isoflavones from soy and lignans from flaxseeds.
Estrogen is involved in the development and progression of several chronic diseases, including osteoporosis and hormone-sensitive cancers such as breast cancer. The structural similarity of the phytoestrogens enterolactone and enterodiol from flaxseed and genistein and daidzein from soy suggests that they may interfere with estrogen metabolism. Modulation of estrogen metabolism has the capacity to influence tissue estrogen exposure and therefore breast cancer and osteoporosis.
This study showed that supplementing the diet with about one ounce of ground flaxseed but not with one ounce of soy flour significantly alters the metabolism of estrogen in favor of the less biologically active estrogen metabolite (2OHE1) in postmenopausal women. So, it would seem far wiser to replace soy in the diet with freshly ground flaxseeds to achieve the benefits of phytoestrogens. Not only would this avoid the negative consequences of unfermented soy, but the omega-3 fats in flaxseeds (ALA) likely provide additional benefits as it balances out the higher order fats DHA and EPA and is necessary for optimum health.
American Journal of Clinical Nutrition February 2004;792 318-325