Weight loss and changes in energy metabolism in massively obese adolescents

OBJECTIVE: To investigate the energy metabolism modifications induced by en ergy restriction and weight loss in massively obese adolescents. SUBJECTS: Ten massively obese girls (179 +/- 31% of ideal body weight; age, 13.3-16.4 y) after 2-5 weeks on a low-energy diet and 4.5-11.5 months later , that is, after a substantial weight loss, and eight controls. MEASUREMENTS: Resting energy expenditure (REE) and carbohydrate-induced the rmogenesis (CIT) after a sucrose load (by indirect calorimetry), plasma glu cose sand insulin before and after the sucrose load. RESULTS: After 2-5 weeks on a low-energy diet, REE (7415 +/- 904 kJ/d) was lower than the expected value calculated from the regression equation ol:RE E on fat free mass in controls (P = 0.005). After a 37 +/- 17% reduction in excess weight, REE decreased (6405 +/- 613 kJ/d) and remained lower then t he expected value (P = 0.005). At the early stages of weight loss, the area under the plasma glucose response curve was negatively correlated with CIT (r = -0.80, P = 0.01) and was higher in the? six obese adolescents with lo w GIT than in the four with normal CIT (396 +/- 52 vs 283 +/- 26 mmol.l(-1) .min(-1), P = 0.01). After substantial weight loss, the area under the plas ma insulin response curve decreased by 32% (P = 0.02), and both CIT and the area under the plasma glucose response curve became similar in obese patie nts with low and normal CIT prior to weight loss. CONCLUSION: These results indicate that in massively obese adolescents, REE for fat-free mass is decreased at the very beginning of the process of los ing weight end remains decreased as long as energy restriction and weight r eduction carry on. They also indicate that the impaired CIT sometimes obser ved returns to normal after weight reduction suggesting that it is secondar y to a decrease in glucose uptake induced by obesity-associated insulin res istance.