Effects of high- and low-isoflavone (phytoestrogen) soy foods on inflammatory biomarkers and proinflammatory cytokines in middle-aged men and women

This study sought to determine effects of high- and low-isoflavone soy protein foods on acute-phase proteins and proinflammatory cytokines and whether isoflavone phytoestrogens might act as estrogens, which enhance the immune response. Forty-one hypercholesterolemic men and postmenopausal women underwent three 1-month diets consisting of a low-fat dairy food control phase and high- and low-isoflavone soy food test phases (50 g/d and 52g/d soy protein, respectively, and 73 mg/d and 10 mg/d isoflavone, respectively). Diets were low in saturated fat (<5% of energy) and cholesterol (<50 mg/d). Fasting blood analytes and blood pressure were measured at the start and end of each phase. For the entire group of subjects, no treatment differences were observed for acute-phase proteins or proinflammatory cytokines. However, a significant interaction was noted between diet and sex. Assessing the results of men and women separately, women showed significantly higher interleukin-6 (IL-6) values after the high-isoflavone soy diet (P = .013) compared to control values. For women, the difference between the high- and low-isoflavone IL-6 values was significant using the unadjusted data (P = .048) but not after adjustment. No significant effects were seen for men or women in C-reactive protein (CRIP), serum amyloid A (SAA), or tumor necrosis factor-alpha (TNF-alpha). Thus, high levels of isoflavone intake appear to increase serum concentrations of IL-6 in women. This finding may indicate an estrogenic effect of soy isoflavones in enhancing the immune response and provide a possible explanation through enhanced immune surveillance for lower incidence of certain cancers in soy-eating parts of the world. Copyright 2002, Elsevier Science (USA). All rights reserved.