Effects of four weeks of daily soy milk or dairy milk ingestion on the exercise induced inflammatory and oxidative responses in plasma and skeletal muscle in a post-menopausal female population.

The process of senescence is associated with increasing inflammation and subsequent oxidative stress in the body, both of which can exert negative health effects at local and systemic levels. Attenuation of such processes with novel dietary countermeasures has major public health implications. Soyfoods, as a source of high quality protein, minimal saturated fat, and unique composition of isoflavones may improve such indices, although such effects in healthy older women are not well delineated. To explore this supposition, a single-blind, randomized, controlled trial was conducted on 31 postmenopausal women at Baylor University, Waco TX. After a two week run-in period, subjects were randomly assigned to consume three servings of vanilla soy (n=16) or reduced-fat dairy (n=15) milk per day for four weeks. Parameters of systemic inflammation (TNF-α, IL-1β, IL-6) and oxidative stress (SOD, GPx, COX-2) as well as expression of local inflammation-responsive genes (TNF-α, IL-1β, IL-6, COX-2, NF-κB) were measured prior to supplementation, at four weeks post supplementation, and after an eccentric exercise bout performed to elicit an inflammatory response. A significant group by time effect for plasma TNF-α was observed (p = 0.04), with TNF-α values for the soy group appearing to stay consistent during the exercise period, while the TNF-α values for the dairy group increased post-supplementation, decreased from T2-T4, and then returned to baseline by T6. Significant time effects were observed for plasma SOD (p < 0.0001) and IL-6 (p < 0.0001), and muscle expression of IL-6 (p < 0.01) and IL-1β (p<0.01). Despite good dietary compliance, overall results from our study do not support the notion that four weeks of daily soy milk ingestion can attenuate systemic or local elevations in markers of oxidative stress or inflammation. However, data do suggest that the downhill running protocol utilized in this study can be effective at altering systemic and local markers of inflammation, and that ingestion of soy may help to maintain plasma TNF-α levels even when exposed to a stress inducing stimulus, although more data exploring this conjecture is certainly warranted.