Legume Consumption Improves Cellular Health and Autonomic Function in Competitive Swimmers

<b>Objective:</b> This study evaluated whether higher adherence to the Mediterranean Diet (MD), specifically through increased legume consumption, is associated with improved functional, autonomic, and performance parameters in adolescents and young adult competitive swimmers. <b>Methods</b>: Thirty-nine swimmers (mean age 19.7 ± 2.3 years; 22 men, 17 women) monitored over a five-month period under standardized training conditions. Based on baseline dietary assessment, participants were allocated into three groups according to habitual legume intake: Control group (<1 serving/week, no dietary modification), 3Legumes group (~2 servings/week, increased to 3/week), and 6Legumes group (~3-4 servings/week, increased to 6/week). Functional evaluation encompassed bioelectrical impedance parameters (phase angle, extracellular and intracellular water, ECW/ICW ratio), heart rate variability (HRV), cardiac coherence, and critical swimming speed test (CSS) results. <b>Results</b>: After 5 months, the 6Legumes group showed an increase in phase angle (Δ = +0.34 ± 0.35°, <i>p</i> = 0.004), a reduction in extracellular water (Δ = -1.77 ± 0.93%, <i>p</i> < 0.001), and an increase in intracellular water (Δ = +1.77 ± 0.93%, <i>p</i> < 0.001), resulting in a lower ECW/ICW ratio (Δ = -0.051 ± 0.028, <i>p</i> < 0.001). HRV (Δ = +6.92 ± 5.02, <i>p</i> = 0.0003) and cardiac coherence (Δ = +0.40 ± 0.35, <i>p</i> = 0.0015) also demonstrated statistically significant improvements, whereas CSS exhibited a positive trend (Δ = +0.011 ± 0.019 m/s, <i>p</i> = 0.067) without reaching statistical significance. Between-group comparisons confirmed significant differences in phase angle and water-distribution parameters (all <i>p</i> < 0.01). <b>Conclusions</b>: In this cohort of adolescents and young adult competitive swimmers, increased legume consumption within a Mediterranean dietary framework was associated with beneficial adaptations in cellular hydration status, autonomic regulation, and functional performance.