Soy Consumption and Phytoestrogens: Effect on Serum Prostate Specific Antigen When Blood Lipids and Oxidized Low-Density Lipoprotein are Reduced in Hyperlipidemic Men

Purpose: Herbal remedies high in phytoestrogens have been shown to reduce serum prostate specific antigen (PSA) and have been proposed as a treatment for prostate cancer. Soy proteins used to lower serum cholesterol are rich sources of phytoestrogens. Therefore, we assessed the effect of soy consumption on serum PSA in men who had participated in cholesterol lowering studies.Materials and Methods: For 3 to 4 weeks 46 healthy middle-aged men with a range of starting PSA values took soy (mean 44 gm. soy protein daily, 116 mg. isoflavones daily) or control foods, and a subgroup of men took a lower level of soy supplements for 3 months. PSA was measured at the start and end of each treatment.Results: Soy had no significant effect on serum total or free PSA, independent of PSA starting value or isoflavone intake. The lack of effect on PSA was seen, although soy intake was sufficient to reduce low-density lipoprotein cholesterol (5.8 ± 2.2%, p = 0.012), the estimated coronary heart disease risk (6.1 ± 2.8% for ...