Resting energy expenditure is associated with insulin resistance and inflammatory status before and after weight loss in patients with severe obesity

Introduction: Resting energy expenditure (REE) is mainly driven by body composition but tends to decline after caloric restriction more than what is expected according to body composition changes (metabolic adaptation). Determinants of REE beyond body composition values are less known. Our aim was to investigate the role of metabolic and inflammatory markers in determining REE and metabolic adaptation after weight loss. Methods: REE (indirect calorimetry), body composition (fat-free mass or FFM, fat mass or FM by bioelectrical impedance analysis), metabolic markers (fasting plasma glucose, fasting insulin, HOMA index, lipids levels) and adipocytokines (leptin, TNF-alfa, IL-6, hsCRP) were determined before and after weight loss in 175 patients with severe obesity (mean BMI:44.6 ± 7.4 kg/m2) treated with laparoscopic sleeve gastrectomy (LSG) or a lifestyle modification program. Results: At baseline, REE values were significantly related to sex (male = 1; female = 2; r = -0.593; p < 0.001), BMI (r = 0.600; p < 0.001), FFM (r = 0.758; p < 0.001), FM (r = 0.388; p < 0.001) waist (r = 0.664; p < 0.001), HDL-cholesterol (r = -0.225; p < 0.01), fasting glucose (r = 0.166; p < 0.05), fasting insulin (r = 0.301; p < 0.001), HOMA index (r = 0.305; p < 0.001), hsCRP (r = 0.214; p < 0.01). Only FFM, FM and HOMA index were independently related to baseline REE in a multiple regression model. Weight loss was 28.1 ± 11.2% of the baseline body weight. 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 was168 ± 230 kcal/day. Metabolic adaptation was significantly related to the reduction of hsCRP observed after weight loss (r = 0.172; p < 0.05). Conclusion: REE was independently associated with body composition values and insulin-resistance state in patients with severe obesity. Metabolic adaptation during weight loss, defined as any reduction of REE beyond what is can be expected by FFM and FM loss, was related to the improvement of inflammatory status after body weight reduction. Conflict of Interest: None Disclosed Funding: No Funding