Changes in body composition over 5 years after Roux-en-Y Gastric Bypass and Sleeve Gastrectomy

Abstract

Background and aim: Bariatric surgery produces extensive weight loss unrivalled by non-surgical obesity treatments. However, there is limited evidence comparing the effects of different procedures on body composition beyond the first year. Findings are often further limited by body composition assessment methods with unreliable or unproven validity in individuals with obesity. This thesis aimed to compare changes in body composition over five years following two types of bariatric surgery: Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). Secondly, it aimed to assess the validity of bioimpedance techniques for measuring body composition in a population with obesity using dual-energy x-ray absorptiometry (DXA) as a reference standard. Methods: This thesis analysed data collected from participants randomised to undergo either RYGB or SG. Data was collected two days before surgery, one year after surgery, and five years after surgery. Body composition was measured using DXA, single-frequency bioelectrical impedance analysis (SF-BIA) and multi-frequency bioimpedance analysis (MF-BIA). Assessment outcomes included body weight, fat-free mass, appendicular skeletal muscle mass, fat mass, visceral adipose tissue mass, and android adipose tissue mass. Results: Body composition assessment information was available for 91 participants. Compared to the SG group at five years, the RYGB group had more significant reductions in body weight measured as percentage excess weight loss (%EWL) (p<0.0001), total body fat (p<0.0001), body fat percentage (p=0.002), android fat mass (p<0.001), and visceral fat mass (p<0.001), and a more significant increase in fat-free mass percentage (p=0.003). Fat mass and fat-free mass derived from five BIA equations were compared against DXA measurements. Bias ranged from -8.2% to 10.23% of DXA values, and Pearson correlation coefficients exceeded 0.94. However, the limits of agreement were large for all five equations. Conclusions: Greater weight loss was achieved following RYGB due to greater initial weight loss and lower weight regain. Qualitative changes in body composition appear similar between the groups, and differences are likely associated with the extent of weight loss. Factory BIA equations and equations extracted from pre-existing literature failed to estimate body composition in a population with obesity accurately. Without derivation and validation of specific equations for obesity, SF-BIA & MF-BIA applications remain limited by poor individual accuracy and large limits of agreement.