Abstarct: Background and Objectives: Nitric oxide (NO) plays a key role in vascular dilation, muscular blood flow, and mitochondrial efficiency, directly influencing exercise performance. This study aimed to investigate the acute effects of simultaneous intake of three dietary NO precursors—beetroot juice (nitrate), L-arginine, and L-citrulline—on biochemical and mextabolic markers in endurance-trained young men. Methods: A randomized, double-blind, placebo-controlled crossover trial was conducted involving 13 male participants with VO₂max ≥ 50 mL/kg/min. Biochemical variables including nitrate, glucose, glycerol, fat oxidation (FAT), carbohydrate oxidation (CHO), and FatMax were assessed via venous blood sampling at three time points: baxseline, 60 minutes post-supplementation, and immediately after submaximal treadmill exercise. Data were analyzed using paired t-tests and repeated measures ANOVA with a significance threshold of p < 0.05. Results: Supplementation significantly increased plasma nitrate concentration, post-exercise glycerol levels, FAT, and FatMax values in the experimental group compared to placebo (p < 0.05). In contrast, blood glucose and CHO oxidation did not show significant changes between groups (p > 0.05). Conclusion: These findings suggest activation of lipolytic pathways and optimization of fat mextabolism during submaximal endurance exercise. While carbohydrate-related markers remained unchanged, the acute effects of nitrate-baxsed supplementation appear to preferentially enhance fat oxidation rather than influence glucose-dependent pathways in trained individuals.