Objective: To investigate the influence of changes in energy balance and body composition on the rate of weight loss throughout 1 year of Roux-en-Y gastric bypass.
Methods: Variables were collected pre-, 6, and 12 months (M) post-surgery from 18 women (BMI ≥ 40 and ≤ 50 kg m-2, 20 to 45 years). Total energy expenditure (TEEm), fat-free mass (FFM), and fat mass (FM) were measured by doubly labeled water. Self-reported energy intake (EIsr) was obtained from three non-consecutive food diaries. Metabolic adaptation was assessed via deviations from TEE predictive equation, and the calculated energy intake (EIc) via the sum of TEE and change in body stores.
Results: BMI significantly decreased (mean ± SD) from 45 ± 2 kg m-2 to 32 ± 3 kg m-2 at 6 M, and to 30 ± 3 kg m-2 at 12 M after surgery. The TEEm reduced significantly at both time points when compared with pre-surgery (6 M: - 612 ± 317 kcal day-1; 12 M: - 447 ± 516 kcal day-1). At 6 M, a metabolic adaptation was observed and the energy balance was - 1151 ± 195 kcal day-1, while at 12 M it was - 332 ± 158 kcal day-1. Changes in the values of TEEm were associated with changes in body weight at 12 M post-surgery. A significant underreporting was observed for EIsr (1057 ± 385 kcal day-1) vs. EIc (2083 ± 309 kcal day-1) at 12 M post-operative.
Conclusion: The higher rate of weight loss at 6 M post-surgery was a response to energy imbalance, which was caused by high restriction in energy intake even with the presence of metabolic adaptation at this time. The EIsr was not sufficiently accurate to assess the energy consumption of this population.
Registration of clinical trials (observational study): Brazilian Clinical Trials Registry: RBR-8k5jsj. Universal Trial Number: U1111-1206-0858.
Keywords: Bariatric surgery; Body composition; Doubly labeled water; Energy balance; Metabolic adaptation.