Enhancement of Lower Limb Muscle Strength and Reduction of Inflammation in the Elderly: A Randomized, Double-Blind Clinical Trial Comparing Lacticaseibacillus paracasei PS23 Probiotic with Heat-Treated Supplementation

Background: As individuals age, there is a gradual loss of muscle mass and strength, which not only impairs physical functionality but also heightens the risk of falls and diminishes independence among older adults. Probiotics have emerged as a focus of recent research due to their potential role in enhancing muscle health via the gut–muscle axis. This study evaluates the effects of live and heat-treated Lacticaseibacillus paracasei PS23 (PS23) supplementation on muscle strength and mass in the elderly. Methods: This study recruited 119 participants, aged 65–85 years, and randomly assigned them to receive a placebo (0 × 10¹⁰ CFU/day), L-PS23 (live PS23, 2 × 10¹⁰ CFU/day), or HT-PS23 (heat-treated PS23, 2 × 10¹⁰ cells/day) for a duration of 12 weeks. Assessments of blood pressure, body composition, muscle strength, functional physical fitness, and biochemical parameters were conducted at baseline, 6 weeks, and 12 weeks. Results: Among the 100 subjects who completed the trial, supplementation with both L-PS23 and HT-PS23 significantly enhanced lower limb muscle strength and endurance compared to the placebo (p < 0.05), although no significant differences were observed in muscle mass or upper limb muscle strength across the groups. Additionally, while most muscle anabolism-related markers showed no significant changes, both supplements effectively decreased inflammatory markers related to aging—C-reactive protein (CRP: L-PS23, p = 0.016; HT-PS23, p = 0.013) and interleukin-6 (IL-6: L-PS23, p = 0.003; HT-PS23, p < 0.001)—and increased interleukin-10 levels (L-PS23, p = 0.014; HT-PS23, p = 0.005). Notably, only the HT-PS23 group demonstrated a significant increase in testosterone levels (p = 0.029). Conclusions: 12 weeks of supplementation with L-PS23 and HT-PS23 improved lower limb muscle strength and endurance but did not significantly enhance muscle mass in older adults. Both supplements also proved effective in reducing inflammatory markers and elevating testosterone levels. HT-PS23, administered as a heat-treated probiotic, provided more pronounced benefits to the elderly compared with its probiotic counterpart, L-PS23.