Secondary Hypogonadism due to Excessive Ingestion of Isoflavone in a Man

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A 54-year-old man had been drinking approximately 1.2 L of soy milk (equivalent to approximately 310 mg of isoflavones) per day for the previous 3 years. He then developed erectile dysfunction and gynecomastia. On an examination in our department in May, blood tests showed low gonadotropin and testosterone levels, indicative of secondary hypogonadism. He stopped drinking soy milk on his own in June of that year. When he was admitted in August, blood tests showed an improved gonadal function. Secondary hypogonadism caused by the excessive intake of isoflavones in soy milk was diagnosed. In men, an excessive intake of isoflavones may cause feminization and secondary hypogonadism.