Purpose <p>Malnutrition affects up to 54% of hemodialysis patients and is associated with increased mortality. We evaluated the effects of probiotic and synbiotic supplementation on nutritional status in maintenance hemodialysis patients.</p> Methods <p>This single-blind randomized-controlled trial enrolled 60 hemodialysis patients randomly assigned to receive Lactobacillus plantarum (10 billion CFU twice daily), synbiotic (L. plantarum plus 3&#xa0;g oat fiber β-glucans daily), or standard care for 24&#xa0;weeks. Primary outcomes included triceps skinfold thickness, normalized protein catabolic rate (nPCR), and body mass index (BMI). Secondary outcomes included serum albumin, total protein, cholesterol, and leptin.</p> Results <p>All 60 patients completed the trial. Triceps skinfold thickness increased significantly in the probiotic group (3.3 ± 2.2&#xa0;mm) and synbiotic group (4.7 ± 2.2&#xa0;mm) compared to placebo (0.0 ± 1.6&#xa0;mm, <i>p</i> &lt; 0.001). BMI increased more in treatment groups (probiotic: 1.4 ± 1.0&#xa0;kg/m²; synbiotic: 1.7 ± 0.4&#xa0;kg/m²) than in the placebo group (0.7 ± 0.9&#xa0;kg/m², <i>p</i> &lt; 0.001). The probiotic group showed a significant within-group increase in albumin (0.25 ± 0.37 g/dL, <i>p</i> = 0.008), though between-group differences were not significant. No significant changes occurred in nPCR, total protein, cholesterol, or leptin. No serious adverse events were reported.</p> Conclusion <p>Probiotic and synbiotic supplementation safely and effectively improved anthropometric nutritional markers in hemodialysis patients, representing feasible adjunctive strategies for managing malnutrition.</p> Trial registration <p>ClinicalTrials.gov NCT06891105 (prospectively registered April 2025).</p>