Resting energy expenditure after Roux-en Y gastric bypass surgery.

BACKGROUND: The mechanisms by which Roux-en Y gastric bypass surgery (RYGB) provokes weight loss are incompletely understood. Enhanced energy expenditure may be one contributing mechanism. Previous results on changes in resting energy expenditure (REE) after RYGB are inconsistent.

OBJECTIVES: The aim of the present study was to assess changes in REE after RYGB and whether REE predicts weight loss (percentage weight loss).

SETTING: Obesity Clinic.

METHODS: REE was measured by indirect calorimetry (mREE) before and 1 year after RYGB in 233 patients with severe obesity (175 women; all body mass index ≥35.0 kg·m-2 ) and mREE was compared with predicted REE (pREE) and expressed as percentage of pREE (%pREE). For calculation of pREE, 2 new equations were developed from an independent reference group of overweight and obese patients (852 patients; body mass index range: 27.4-73.0 kg·m-2 ) that were examined in exactly the same setting as the bariatric patients that were followed-up after RYGB. The new equations were based on either anthropometric (pREE-BM, %pREE-BM) or body composition (pREE-BC; %pREE-BC) parameters.

RESULTS: After RYGB, absolute mREE was reduced by 20.4 ± 11.0% (-458 ± 277 kcal·d-1 ; P<.001). Compared with pREE-BM (post-%REE-BM) and pREE-BC (post-%REE-BC), mREE was 2.3 ± 9.4% and 1.6 ± 9.5%, respectively, higher (both P ≤ .03). Post-%pREE-BM and post- %pREE-BC after RYGB were positively correlated with percentage weight loss (r = .206 and r = .231; both P ≤ .003).

CONCLUSIONS: Data indicate a slightly higher mREE than pREE after RYGB. Although the underlying mechanisms of this observation remain to be elucidated our finding may play a role for weight loss outcomes after the surgery.