Objective: To review the sources, metabolism, potencies, and clinical effects of phytoestrogens on humans.
Data sources: The MEDLINE data base for the years 1980-1995 and reference lists of published articles were searched for relevant English-language articles concerning phytoestrogens, soy products, and diets with high-phytoestrogen content.
Methods of study selection: We identified 861 articles as being relevant. Human cell line studies, human epidemiologic studies (case-control or cohort), randomized trials, and review articles were included. Animal studies regarding phytoestrogens were included when no human data were available concerning an important clinical area.
Tabulation, integration, and results: Included were studies containing information considered pertinent to clinical practice in the areas of growth and development, menopause, cancer, and cardiovascular disease. When findings varied, those presented in this study reflect consensus. All studies concurred that phytoestrogens are biologically active in humans or animals. These compounds inhibit the growth of different cancer cell lines in cell culture and animal models. Human epidemiologic evidence supports the hypothesis that phytoestrogens inhibit cancer formation and growth in humans. Foods containing phytoestrogens reduce cholesterol levels in humans, and cell line, animal, and human data show benefit in treating osteoporosis.
Conclusion: This review suggests that phytoestrogens are among the dietary factors affording protection against cancer and heart disease in vegetarians. With this epidemiologic and cell line evidence, intervention studies are now an appropriate consideration to assess the clinical effects of phytoestrogens because of the potentially important health benefits associated with the consumption of foods containing these compounds.