The purpose of this research study is to examine the safety of specific soy components, known as isoflavones, and to find out what effects (good and bad) these components have on tissues that are sensitive to the hormone estrogen in healthy, post-menopausal women. Isoflavones are compounds that occur naturally in soybeans and can be extracted to put in to capsule form or add to foods. The capsule formulation being used in this study is considered an investigational drug. This research is being done because many scientists believe that isoflavones may play a role in the prevention of some kinds of cancer. While isoflavones have been safely consumed in foods for centuries, we need to know if these soy components are safe to take in higher doses when they are extracted from foods and provided in a supplement form. We plan to test the safety and effects of the soy isoflavones known as genistein, daidzein and glycitein.