Soy foods and supplementation: a review of commonly perceived health benefits and risks.

In recent years, the impact of soy foods and supplements upon human health has become increasingly controversial among the general public. No one has conducted a broad evaluation of the scientific evidence supporting or refuting popular perceptions of the health effects of soy consumption. In this article, the authors have conducted a comprehensive assessment of the literature surrounding the health effects of soy consumption that are of greatest interest. This review has focused on 5 health benefits- relief of menopausal symptoms and prevention of heart disease, breast cancer, prostate cancer, and osteoporosis, and 5 health risks-increased risk of breast cancer, male hormonal and fertility problems, hypothyroidism, antinutrient content, and harmful processing by-products. Systematic reviews of human trials, prospective human trials, observational human studies, animal models, in vitro studies, and laboratory analyses of soy components were included for review. This literature review revealed that soy foods and isoflavones may provide relief from menopausal symptoms and protect against breast cancer and heart disease. Soy does not appear to offer protection against osteoporosis. The evidence on male fertility and reproductive hormones was conflicting; some studies demonstrated a deleterious impact caused by soy consumption and others showed no effect. Soy supplementation also appears to affect thyroid function in an inconsistent manner, as studies have shown both increases and decreases in the same parameters of thyroid activity. Soaking, fermentation, and heating may reduce problematic antinutrients contained in soy. The authors found that consuming moderate amounts of traditionally prepared and minimally processed soy foods may offer modest health benefits while minimizing potential for adverse health effects. However, additional studies are necessary to elucidate the variable thyroid response to soy supplementation, and more rigorous studies are required to assess dose-response relationships, the relationship between intestinal-flora composition and the response to soy, potential fertility issues among males, and the unknown long-term health effects of consuming highly processed modern soy foods.