Dietary isoflavones or isoflavone-rich food intake and breast cancer risk: A meta-analysis of prospective cohort studies

Previous studies implied that dietary isoflavone intake may reduce the risk of developing breast cancer, but some have shown ambiguous results. This study aimed to systematically evaluate and summarize available evidence on the effect dietary isoflavone intake has on the risk of developing breast cancer.PubMed, Embase, and the Cochrane Library were searched for prospective cohort studies published through April 2017 that evaluated the effect of dietary isoflavone intake on the development of breast cancer.Sixteen prospective cohort studies, involving 11,169 breast cancer cases and 648,913 participants, were identified and included in our data analysis. The pooled relative risk (RR) of breast cancer was 0.99 for high versus low intake of isoflavones (95% confidence interval [CI], 0.91-1.09; P = 0.876) and 0.99 for moderate versus low intake of isoflavones (95%CI, 0.92-1.05; P = 0.653), with insignificant heterogeneity (P = 0.187 for high versus low, and P = 0.192 for moderate versus low). While a moderate consumption of soy-based foods did not significantly affect breast cancer risk, a high intake of soy-based foods associated with a lower risk of developing breast cancer. Considering specific foods, an increased the risk of developing breast cancer was seen with a moderate intake of formononetin, but no significant associations were found between breast cancer risk and other isoflavone-rich diets.The present meta-analysis indicates that women with a high dietary intake of soy foods may experience a statistically significant reduction in breast cancer risk. However, moderate formononetin consumption may increase the risk of developing breast cancer.