Soymilk supplementation does not alter plasma markers of inflammation and oxidative stress in postmenopausal women

Aging is associated with increasing levels of systemic inflammation and oxidative stress, both of which contribute to the progression of cardiovascular disease. Attenuation of such processes via dietary intervention has significant public health implications. Soyfoods, as a source of high-quality protein and isoflavones, may improve such indices, although such effects in healthy aging women are not well delineated. The purpose of this study was to test the hypothesis that 4 weeks of daily soymilk consumption would improve systemic markers of inflammation and oxidative stress in postmenopausal women when compared with a dairy control. In September 2009, a single-blind, randomized, controlled trial was conducted on 31 postmenopausal women at Baylor University, Waco, Tex. Subjects were randomly assigned to consume 3 servings of vanilla soy (n = 16) or reduced fat dairy (n = 15) milk per day for 4 weeks. Plasma markers of inflammation (tumor necrosis factor α [TNF-α], interleukin [IL]-1β, IL-6) and oxidative stress (superoxide dismutase [SOD], glutathione peroxidase [GPx], cyclooxygenase-2 [COX-2]) were obtained before and after supplementation. No significant differences were observed for any of the plasma inflammatory (TNF-α, P = .08; IL-1β, P = .14; IL-6, P = .26) or oxidative stress (SOD, P = .68; GPx, P = .58; COX-2, P = .99) variables by dietary treatment group. Despite good dietary compliance, our study failed to show a significant effect of soymilk consumption on markers of inflammation and oxidative stress in this postmenopausal female population. Potential reasons for this nonsignificant finding are discussed, and future research directions are presented.