Effects of Soy Pretzel Consumption on Blood Biomarkers and Muscle Soreness After Intense Resistance Exercise in Healthy, Trained Males: A Preliminary Study

Abstract

McClure, J, Sommer, A, Kraemer, WJ, and Vodovotz, Y. Effects of soy pretzel consumption on blood biomarkers and muscle soreness after intense resistance exercise in healthy, trained males: a preliminary study. J Strength Cond Res 40(4): 422-430, 2026-Intense resistance exercise can cause exercise-induced muscle damage (EIMD), resulting in inflammation and muscle soreness. Soy protein and its isoflavones have been hypothesized to reduce inflammation, enhance antioxidant capacity, and support recovery. This preliminary study examined the effects of a soy soft pretzel (SSP) on soreness and biomarkers of EIMD. Ten trained male athletes aged 19-29 years completed a double-blind, randomized, crossover trial with either SSP or a wheat pretzel (control). Muscle soreness was measured using a visual analog scale, and blood samples were analyzed for markers of inflammation and muscle damage. Urinary isoflavones were measured to confirm compliance. Serum testosterone was notably lower after SSP (14.54 ± 5.07 nmol·L -1 ) than wheat (16.35 ± 5.76 nmol·L -1 ; p = 0.0072; d = -0.60). Although interleukin-6 levels declined more quickly starting at 6 hours in the SSP group ( d ≈ -0.50), this difference was not statistically significant. Urinary daidzein, genistein, and glycitein levels were all significantly higher ( p < 0.001, 0.011, and 0.011; d > 1.0), indicating absorption of soy isoflavones. Soreness ratings showed no significant difference between treatments, likely because of high individual variability ( d < 0.20). These results suggest that while soy pretzel intake affects hormonal and isoflavone responses, its impact on soreness and inflammatory markers remains uncertain and requires further study with larger, adequately powered samples. Practically, soy-based recovery snacks could be a convenient, athlete-friendly option that is generally well tolerated; however, coaches and sports nutritionists should interpret these findings as preliminary until more definitive evidence becomes available.

Keywords: athletes; inflammation; nutrition; recovery.