The Effects of Multi-Strain Probiotic SLAB51 Intake on Aerobic Performance and Oxidative Stress Responses in Elite Athletes: A Randomized Crossover Trial

Background/Objectives: Exercise performance and recovery depend on interactions between energy metabolism and redox regulation. SLAB51, a multi-strain probiotic, may influence oxygen-related metabolism and antioxidant responses, but evidence in elite athletes remains limited. This study aimed to evaluate the effects of SLAB51 supplementation on aerobic exercise capacity and oxidative stress responses in elite athletes. Methods: This randomized, double-blind, placebo-controlled crossover trial evaluated the effects of SLAB51 supplementation on aerobic exercise performance and oxidative stress in elite athletes. Participants received SLAB51 and placebo for one week each, separated by a two-week washout period. Assessments were performed at baseline, after a single intake, and after one week of intake. Exercise performance was evaluated using a treadmill-based Bruce protocol, and physiological and oxidative stress markers were measured. Data were analyzed using two-way repeated-measures analysis of variance (ANOVA), supplemented by post hoc linear mixed-effects models (LMMs) accounting for the crossover design. Results: The original ANOVA showed significant treatment × time interactions for exercise duration, duration above a respiratory exchange ratio (RER) of 1.0, and pre-exercise superoxide dismutase (SOD) activity, but not for maximal oxygen uptake, lactate removal, or malondialdehyde concentration. The additional post hoc LMM analysis also identified a significant treatment difference in exercise duration after one week (mean difference = 33.32 s, 95% CI: 17.42–49.22, p < 0.001), with significant differences in duration above RER 1.0 and SOD activity also observed after one week. Conclusions: These findings support the potential benefits of one-week SLAB51 supplementation for exercise duration in elite athletes, consistent with the additional crossover-adjusted analysis. Favorable differences in duration above RER 1.0 and pre-exercise antioxidant enzyme activity warrant further investigation.