Modifications of Resting Energy Expenditure after surgical or medical weight loss: Is there any difference?

Background/Aim: Resting energy expenditure (REE) tends to decline after caloric restriction more than what is expected according to body composition changes. This metabolic adaptation is considered one of the factors favoring weight regain and obesity recidivism. Weight maintenance is more common after bariatric surgery than after medical weight loss. Our Aim: was to evaluate if metabolic adaptation is different after surgical or medical weight loss. Methods: REE (indirect calorimetry) and body composition (fat-free mass or FFM, fat mass or FM by bioelectrical impedance analysis) were determined before and after a 12 months weight loss in 98 obese patients (mean BMI: 46.8 ± 8.0 kg/m2) treated with laparoscopic sleeve gastrectomy (LSG) and in 21 obese patients (mean BMI: 35.1 ± 15.0 kg/m2) reaching at least a 10% weight loss with a lifestyle modification program. Results: Weight loss was 28.3 ± 9.2% of the baseline body weight in the surgical group and 18.5 ± 6.2% in the medical group (p < 0.001), with corresponding relative reductions in FM (44.4 ± 18.0 vs 34.7 ± 13.0%, p < 0.05), FFM (13.1 ± 8.0 vs 6.1 ± 7.3%, p < 0.01), and REE (28.3 ± 12.6 vs 15.0 ± 17.0%, p < 0.01). In order to account for body composition changes, a predictive equation for REE was derived by using the baseline FFM and FM values. A predicted post-weight loss REE was then calculated by using this equation and by entering the individual body composition values measured after weight loss. Metabolic adaptation was defined as the difference between observed and predicted REE after weight loss. Metabolic adaptation was -182 ± 227 kcal/day in the surgical group and -86 ± 212 kcal/day in the medical group (p = not significant). Conclusion: Metabolic adaptation during weight loss, defined as any reduction of REE beyond what is can be expected by FFM and FM loss, was not significantly different in patients losing weight after LSG and in patients losing weight by lifestyle modifications. Weight maintenance after bariatric surgery seems not to be attributable to differences in REE adaptation during weight loss.