Impact of fluid overload on body composition and nutritional status in hemodialysis patients: insights from a prospective study

Background: Chronic fluid overload (overhydration, OH) is common in maintenance hemodialysis (HD) and linked to adverse clinical and nutritional profiles. We investigated whether persistent OH selectively impairs lean tissue during long-term follow-up. Methods: In a single-center prospective cohort of 107 adults on thrice-weekly HD, body composition was assessed by multi-frequency bioimpedance spectroscopy at baseline, 12, 24, and 36 months. Lean tissue index (LTI), fat tissue index (FTI), phase angle (PhA), and OH were recorded. Patients were categorized into high vs. low OH groups by cohort mean relative OH. Multivariable linear regression (adjusting for age, sex, Kt/Vurea, high-sensitivity C-reactive protein, and FTI) and linear mixed-effects models were performed for cross-sectional and longitudinal analyses. Results: Mean age was 64.0 ± 11.9 years; 54.2% were male. The high-OH group had lower LTI (12.7 ± 3.0 kg/m2 vs. 14.7 ± 3.2 kg/m2, p = 0.001), PhA (3.76 ± 0.73° vs. 4.95 ± 0.89°, p < 0.001), and body cell mass index (6.89 ± 2.09 kg/m2 vs. 8.32 ± 2.25 kg/m2, p < 0.001), with similar FTI (9.0 ± 4.1 kg/m2 vs. 9.2 ± 5.3 kg/m2, p = 0.770). Weight loss >10% was more frequent in the high-OH group (20.4% vs. 3.8%, p = 0.008). Relative OH was independently and inversely associated with LTI cross-sectionally (β = -0.114, p < 0.001) and longitudinally as a time-varying covariate (β = -0.039, p = 0.020). Mixed-effects models showed persistent between- group differences in LTI and PhA over 36 months. Conclusion: Sustained OH was independently associated with lower lean tissue mass, impaired cellular integrity, and greater weight loss, but not fat mass. Routine body cell mass monitoring may help identify patients at risk of sarcopenia and support timely fluid and nutritional interventions.