Longitudinal changes in bioelectrical impedance-derived body composition after sleeve gastrectomy in patients with...

Weight loss after bariatric surgery is commonly reported using anthropometric parameters; however, these measures do not distinguish between changes in fat mass, lean tissue, and body water. Bioelectrical impedance analysis (BIA) enables a more detailed assessment of body composition and may provide additional information regarding postoperative physiological adaptations. The present study aimed to evaluate longitudinal changes in BIA-derived body composition over a 24-month follow-up after sleeve gastrectomy (SG) in patients with class III obesity. In addition, exploratory subgroup analyses according to sex and baseline body mass index (BMI) were performed to investigate potential differences in postoperative body composition trajectories.

This retrospective observational study included 49 patients who underwent laparoscopic SG at a tertiary bariatric center. Body composition was assessed preoperatively and at regular postoperative follow-up visits using standardized multifrequency BIA. Parameters included body weight, BMI, fat mass, fat-free mass, skeletal muscle mass, total body water, extracellular water-to-total body water ratio (ECW/TBW), phase angle (PhA), visceral adipose tissue estimate, and resting energy expenditure. Longitudinal changes were evaluated throughout the 24-month observation period. Subgroup analyses should be interpreted with caution because of the limited sample size.

Substantial reductions in body weight, BMI, fat mass, visceral adipose tissue estimate, fat-free mass, skeletal muscle mass, total body water, and estimated resting energy expenditure were observed during follow-up. The largest changes occurred during the first postoperative year and subsequently stabilized. Phase angle decreased during the early postoperative period before showing partial recovery over time. Exploratory subgroup analyses suggested differences in absolute body composition trajectories between men and women as well as between patients with baseline BMI below and above 50 kg/m²; however, these findings should be interpreted within the context of the observational study design and limited statistical power.

Sleeve gastrectomy was associated with marked longitudinal changes in BIA-derived estimates of body composition during the first 24 postoperative months. Besides the expected reduction in fat mass, decreases in fat-free mass and skeletal muscle mass as well as transient changes in phase angle were observed. These findings emphasize the importance of longitudinal body composition assessment following bariatric surgery. Future studies should investigate whether structured nutritional and exercise interventions may further improve postoperative body composition outcomes. Because body composition was assessed exclusively by BIA, the results should be interpreted as impedance-derived estimates rather than direct measurements of individual tissue compartments.