Changes in Total Energy Expenditure and Body Composition After Bariatric Surgery

Background: Bariatric surgery (BS) is the most effective obesity treatment for patients with class III obesity. Some investigators have interpreted slowing body weight (BW) loss with time after BS and later BW regains as evidence of decreased total energy expenditure (TEE). We aimed to measure energy expenditure and analyze within-subject correlations between changes in adjusted TEE and body composition after BS. Methods: Eighteen women with class III obesity (age = 29.5 ± 5.3 years; BMI = 44.7 ± 2.4 kg/m2) who underwent Roux-en-Y gastric bypass (RYGB) participated in the study. Total energy expenditure and body composition were measured using doubly labeled water (DLW) at baseline, and 6m and 12m after RYGB. Adjusted TEE was calculated as measured TEE divided by predicted TEE (adjusted for FFM, FM, age, and the number of steps/BW) and multiplied by 100. A mixed linear model has analyzed the adjusted TEE changes after BS, and the RMCORR package analyzed the repeated measures correlation. Results: The measured TEE reduced significantly at 6m (2292 ± 446 kcal/d) and 12m (2538 ± 336 kcal/day) after RYGB when compared with baseline (2904 ± 547 kcal/d). Adjusted TEE was 94.5% and 106.4%, at 6m and 12m (ß = -11.8; 95% CI = -21.5; 2.2). Our repeated measures correlation analysis showed positive withinsubject associations between changes in BW (rrm = 0.47; 95% CI = 0.00; 0.77) and FFM (rrm = 0.56; 95% CI = 0.11; 0.82) with measured TEE. There was no significant correlation between changes in FM (kg and %) with measured TEE. Conclusions: The decrease in measured TEE partially explains the slowing BW loss rate at 6m, but not at 12m. Metabolic adaptation in the adjusted TEE at 6m contributed to the decrease; however, this adaptation no longer existed at 12m, contributing to increases in measured TEE are associated with rates of BW and FFM losses during the first year after surgery. Thus, in terms of energy balance, the downregulation of the measured TEE is not the major driver of slowing rates of weight loss and body composition throughout 12m after surgery.