Influence of Energy Balance on the Rate of Weight Loss Throughout One Year of Roux-en-Y Gastric Bypass: a Doubly Labeled Water Study.

Abstract

To investigate the influence of changes in energy balance and body composition on the rate of weight loss throughout 1year of Roux-en-Y gastric bypass. Variables were collected pre-, 6, and 12months (M) post-surgery from 18 women (BMI ≥ 40 and ≤ 50kgm-2, 20 to 45years). 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. BMI significantly decreased (mean ± SD) from 45 ± 2kgm-2 to 32 ± 3kgm-2 at 6M, and to 30 ± 3kgm-2 at 12M after surgery. The TEEm reduced significantly at both time points when compared with pre-surgery (6M: - 612 ± 317kcalday-1; 12M: - 447 ± 516kcalday-1). At 6M, a metabolic adaptation was observed and the energy balance was - 1151 ± 195kcalday-1, while at 12M it was - 332 ± 158kcalday-1. Changes in the values of TEEm were associated with changes in body weight at 12M post-surgery. A significant underreporting was observed for EIsr (1057 ± 385kcalday-1) vs. EIc (2083 ± 309kcalday-1) at 12M post-operative. The higher rate of weight loss at 6M 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. Brazilian Clinical Trials Registry: RBR-8k5jsj. Universal Trial Number: U1111-1206-0858.