RESTING METABOLIC-RATE AND POSTABSORPTIVE SUBSTRATE OXIDATION IN MORBIDLY OBESE SUBJECTS BEFORE AND AFTER MASSIVE WEIGHT-LOSS

OBJECTIVE: To investigate the changes of resting metabolic rate (RMR) and postabsorptive oxidation of carbohydrates (CHO), lipids (LIP) and proteins (PT) in morbidly obese subjects after long-term stable massiv e weight reduction. DESIGN: Longitudinal, intervention study of a bili o-pancreatic by-pass. SUBJECTS: Ten (Four men, six women) obese subjec ts (BMI: 53.7 +/- 2.1 kg/m(2), mean +/- s.e.m.) and 12 (three men, nin e women) control subjects (BMI: 21.4 +/- 1.0 kg/m(2)). MEASUREMENTS: R MR and substrates oxidation (indirect calorimetry), body composition ( bioelectrical impedance), plasma concentrations of glucose, FFA, insul in and thyroid hormones before (T0, prior to surgery), during (T1: 1-3 months, and T2: 9-16 months following surgery) and after (T3: 36-42 m onths following surgery) massive weight loss. RESULTS: At T3 BMI prove d to be stably reduced to 32.9 +/- 1.3 (P < 0.0001). The RMR progressi vely reduced both in absolute value (T3: -2566 kJ/24 h: P < 0.0001 vs T0) and normalized for fat-free mass (FFM; T0: 123 +/- 3.8. T1: 109 +/ - 3.3. T2: 112 +/- 7.1, T3: 105 +/- 4.6 kJ/kg-FFM 24 . h; P < 0.05). A t T3 the normalized RMR became significantly lower than the correspond ing value of a control group (118 +/- 2.5 kJ/kg-FFM 24 . h; P < 0.01). The long term trend in substrates oxidation showed that CHO oxidation increased while LIP oxidation decreased; PT oxidation did not signifi cantly change for the whole of the study. CONCLUSION: Previously morbi d obese subjects have an energy sparing metabolism and a normal postab sorptive oxidation of LIP and CHO.