Effects of 28 days of dairy or soy ingestion on skeletal markers of inflammation and proteolysis in post-menopausal women

Background: Aging is associated with increased local inflammation and resultant proteolysis in skeletal muscle. In animal models, soy supplementation is a beneficial countermeasure against muscle inflammation and proteolysis; however, the effect on aging humans is not clear. Methods: A single-blinded, randomized, controlled trial was conducted on 31 post-menopausal women. Volunteers were randomly assigned to consume three servings of soy (n=16) or dairy (n=15) milk each day for 28 days. The expression of inflammation- responsive (TNF-α, IL-1β, IL-6) and proteolytic (calpain 1, calpain 2, ubiquitin, E2, atrogin-1, muRF-1) genes in skeletal muscle was determined using real-time polymerase chain reaction before and after supplementation, and then after a downhill run performed to elicit muscle damage. Results: While no group by time interactions were observed, significant main effects for time were observed for IL-1β, IL-6, calpain 2, and atrogin-1 mRNA post exercise. Further analysis revealed that, compared with post-supplementation values, calpain 2 and atrogin-1 mRNA significantly increased at 4 h post exercise (p=0.01 and p<0.01, respectively), whereas IL-1β and IL-6 mRNA significantly decreased at 4 h post exercise (both p<0.01). Conclusions: Soy or dairy milk supplementation at the amount ingested for 28 days does not appear to preferentially inhibit the expression of inflammation-responsive and proteolytic genes that were assessed, and does not attenuate the eccentric exercise-induced upregulation in the proteolytic genes.