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 massive weight reduction.

DESIGN

Longitudinal, intervention study of a bilio-pancreatic by-pass.

SUBJECTS

Ten (Four men, six women) obese subjects (BMI: 53.7 +/- 2.1 kg/m2, mean +/- s.e.m.) and 12 (three men, nine women) control subjects (BMI: 21.4 +/- 1.0 kg/m2).

MEASUREMENTS

RMR and substrates oxidation (indirect calorimetry), body composition (bioelectrical impedance), plasma concentrations of glucose, FFA, insulin 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 months following surgery) massive weight loss.

RESULTS

At T3 BMI proved to be stably reduced to 32.9 +/- 1.3 (P < 0.0001). The RMR progressively 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). At T3 the normalized RMR became significantly lower than the corresponding 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 significantly change for the whole of the study.

CONCLUSION

Previously morbid obese subjects have an energy sparing metabolism and a normal postabsorptive oxidation of LIP and CHO.