Higher dietary soy intake appears inversely related to breast cancer risk independent of estrogen receptor breast cancer phenotypes

The relationship between soy intake (SI) and breast cancer (BC) has been widely investigated with limited information on the significance of hormone receptor status of BC on the association. This study assessed the relationship between SI and BC risk in the context of oestrogen receptor (ER) status of BC. We meta-analyzed data from published studies on SI and BC after a methodical search of EMBASE, PubMed and Cochrane Library through December 2019. Summary estimates with 95% confidence intervals (CI) were presented using a random-effects model. Eighteen (5 cohorts and 13 case-control) studies, were included in this meta-analysis and SI was inversely associated with BC risk [OR (95%) for highest vs. lowest soy food intake = 0.88 (0.84–0.92), P < 0.001, I(2) = 76.1%, Egger's p-value = 0.425] among all women. The inverse relationship was stronger among premenopausal women [OR (95%) = 0.79 (0.71–0.87), P < 0.001, I(2) = 77.3%, Egger's p-value = 0.644]. In addition, SI was inversely associated with BC risk among ER-negative (–) BC women [OR (95%) = 0.71 (0.57–0.90), P = 0.013, I(2) = 72.0%, Egger's p-value = 0.355] and among ER-positive (+) BC women [OR (95%) = 0.87 (0.79–0.96), P = 0.008 I(2) = 74.6%, Egger's p-value = 0.061]. SI appears inversely associated with BC risk, with a stronger inverse association among pre-menopausal and ER-negative BC women.