Context: The purpose of this review is to critically evaluate current research on the effect of soy protein and isoflavone supplements on plasma lipoproteins, and to place the potential role of soy in the prevention of CAD into a clinical perspective.

Evidence Acquisition: An extensive literature search was performed using a variety of medical and scientific databases including Medline, PubMed, Science Direct, Ovid, NIST, and Infotrac, to identify relevant articles. Journal articles were cross-referenced for additional sources of information. Articles were evaluated based on level of experimental control, as well as statistical, quantitative, and clinical analysis.

Evidence Synthesis: Soy and soy isoflavones have been the object of extensive research investigating their potential hypocholesterolemic effects and possible role in the prevention of coronary artery disease (CAD). It has been suggested that soy, especially the isoflavones contained in soy, improves lipoprotein levels, thus reducing the risk for CAD. This belief, however, is not uniformly accepted. Moreover, the experimental evidence in support of this notion is not as overwhelming as generally perceived, and the current available data reveals that the discrepancies observed are primarily statistical in nature rather than reflecting actual quantitative differences in the hypocholesterolemic effects detected.

Conclusion: A critical analysis of the investigations to date indicate the data are not quantitatively impressive and raise substantial questions about the clinical importance of the hypocholesterolemic effects observed.