Associations between preoperative resting energy expenditure and postoperative weight loss after metabolic bariatric surgery - a mid-term observational study

The mechanisms of body weight control after metabolic bariatric surgery (MBS) are complex, involving changes in calorie intake and energy expenditure (EE). Resting energy expenditure (REE), a significant component of total EE, is influenced by body composition. Body mass index (BMI) does not differentiate between fat-free mass (FFM) and fat mass. This study examines changes in REE before and after laparoscopic Roux-en-Y Gastric Bypass (RYGB) and laparoscopic adjustable gastric banding (LAGB) and assesses REE`s association with long-term weight loss. A retrospective, monocentric study analyzed data from 195 RYGB and 94 LAGB cases over 24 years from a Swiss outpatient obesity clinic. Measurements of REE, body composition, and comorbidities were taken at baseline and up to 10 years postoperatively. Linear regression models and Pearson correlations were used to assess correlations between baseline values and total body weight loss (TWL%) at different time points. Given increasing attrition over time, long-term analyses were considered exploratory. There was a significant decrease in BMI, REE, fat mass (FM), and body cell mass (BCM) after both types of surgeries. Preoperative REE did not correlate with TWL at any time point after RYGB, however, it showed a low (R = -0.29), but significant inverse correlation with TWL at 2-years after LAGB. Multiple linear regressions using baseline body composition parameters as dependent variables did not identify any consistent and significant predictor of TWL. Follow-up above 5-years decreased below 50%. This study confirmed a reduction in REE after MBS proportional to weight loss. While preoperative REE may influence short- and mid-term weight loss, its predictive potential for long-term weight loss, especially after RYGB, appears limited, indirectly confirming that decreased caloric intake via reduced meal size and by dietary changes are the main drivers of post-bariatric energic deficit. - REE decreases significantly after metabolic bariatric surgery (MBS). - Higher preoperative REE is linked to lower TWL at 2 years post-surgery after LAGB, but it is not associated to post-RYGB weight loss. - Preoperative REE is not a reliable predictor of long-term weight loss after MBS.