Longitudinal Changes and Persistence of Extracellular Water Distribution After Sleeve Gastrectomy

Background Bioelectrical impedance analysis (BIA) is increasingly used to assess body composition after bariatric surgery. However, longitudinal changes in the extracellular water-to-total body water ratio (ECW/TBW) after laparoscopic sleeve gastrectomy (LSG) and their clinical implications remain poorly understood. This study aimed to characterize perioperative changes in ECW/TBW following LSG and to explore its associations with body composition and clinical parameters. Methods This retrospective single-center study included patients with severe obesity who underwent LSG between 2019 and 2025. Of the 23 patients who underwent surgery during the study period, 16 with complete body composition and laboratory data at all scheduled time points were analyzed. Body composition was assessed preoperatively and at 3, 6, and 12 months postoperatively using multifrequency BIA. Longitudinal changes were evaluated using the Friedman test, and correlations were assessed using Spearman’s rank correlation coefficient. Results The median preoperative body mass index was 46.1 kg/m². Body weight, body mass index, and body fat mass decreased significantly during follow-up (p < 0.001). ECW/TBW increased at 3 months after surgery (median 0.401 vs. 0.390 at baseline) and then decreased slightly at 6 and 12 months (both 0.399), remaining marginally higher than baseline (p < 0.001). Preoperative ECW/TBW correlated positively with body mass index (ρ = 0.566, p = 0.022). At 12 months, ECW/TBW showed a modest inverse correlation with serum albumin (ρ = −0.514, p = 0.042) but was not associated with weight-loss metrics or body composition parameters. A strong positive correlation was observed between preoperative and 12-month ECW/TBW values (ρ = 0.695, p = 0.003). Conclusions ECW/TBW showed a characteristic temporal pattern after LSG, with a transient early postoperative increase followed by partial normalization. Baseline ECW/TBW strongly correlated with postoperative values, suggesting persistence of individual fluid distribution characteristics despite substantial weight loss.