We found that soybean intake reduced the risk of breast cancer (OR = 0.500, 95%CI: 0.291–0.859) and that low soybean intake combined with OPRM1 hypermethylation increased the risk of breast cancer (OR = 5.592, 95%CI: 2.905–10.764). The gene discussed is OPRM1; the disease is breast carcinoma.