Resting Energy Expenditure and Organ-Tissue Body Composition 5 Years After Bariatric Surgery

Introduction Bariatric surgery-induced weight loss may reduce resting energy expenditure (REE) and fat-free mass (FFM) disproportionately thereby predisposing patients to weight regain and sarcopenia. Methods We compared REE and body composition of African-American and Caucasian Roux-en-Y gastric bypass (RYGB) patients after surgery with a group of non-operated controls (CON). REE by indirect calorimetry; skeletal muscle (SM), trunk organs, and brain volumes by MRI; and FFM by DXA were measured at post-surgery visits and compared with CON (N = 84) using linear regression models that adjusted for relevant covariates. Ns in RYGB were 50, 42, and 30 for anthropometry and 39, 27, 17 for MRI body composition at years 1, 2, and 5 after surgery, respectively. Results Regression models adjusted for age, weight, height, ethnicity, and sex showed REE differences (RYGB minus CON; mean +/- s.e.): year 1 (43.2 +/- 34 kcal/day, p = 0.20); year 2 (- 27.9 +/- 37.3 kcal/day, p = 0.46); year 5 (114.6 +/- 42.3 kcal/day, p = 0.008). Analysis of FFM components showed that RYGB had greater trunk organ mass (similar to 0.4 kg) and less SM (similar to 1.34 kg) than CON at each visit. REE models adjusted for FFM, SM, trunk organs, and brain mass showed no between-group differences in REE (- 15.9 +/- 54.8 kcal/day, p = 0.8; - 46.9 +/- 64.9 kcal/day, p = 0.47; 47.7 +/- 83.0 kcal/day, p = 0.57, at years 1, 2, and 5, respectively). Conclusions Post bariatric surgery patients maintain a larger mass of high-metabolic rate trunk organs than non-operated controls of similar anthropometrics. Interpreting REE changes after weight loss requires an accurate understanding of fat-free mass composition at both the organ and tissue levels.