570 Rev Méd Chile 2008; 136: 570-577 Correspondencia a: Dr. Fernando Carrasco. Independencia 1027. Santiago, Chile. Fono: 9786136. Fax: 7378778. E mail: fcarrasc@med.uchile.cl Gasto energético y composición corporal en mujeres con obesidad severa y mórbida sometidas a bypass gástrico Fernando Carrasco 1 , Pamela Rojas 1 , M anuel Ruz 1a , Anabella Rebolledo 1b , Juana Codoceo 1c , Jorge Inostroza 1c , Claudio Mizón 1 , Karin Papapietro 2 , Attila Csendes 2 , Jorge Rojas 2 , Fernando Pizarro 3c , Manuel Olivares 3 . Energy expenditure and body composition in severe and morbid obese women after gastric bypass Background: The effects of gastric bypass (GBP) on resting energy expenditure (REE) are not well known. Aim: To evaluate the changes in REE and its relationship with body composition in severe and morbid obese women before and six and twelve months after GBP. Patients and methods: Twenty three women aged 37 –10 years, with a body mass index of 44 –4 kg/m 2 , were evaluated before, six and twelve months after GBP. REE was measured in a Deltatrac indirect calorimeter and expressed as kcal/day. Fat mass (FM), and fat free mass (FFM) were determined by double beam X ray densitometry (DEXA). Results: Body weight reduction six and twelve months after GBP was 29.0 –4.3 and 35.8 –6.9%, respectively. The best predictor of weight reduction was initial weight (p <0.01). At six and twelve months, REE decreased by 291.7 –260.0 and 353.8 –378.4 kcal/day, respectively. In the same periods REE/kg body weight increased by 3.3 and 4.8 kcal/kg respectively, compared to baseline. REE/kg FFM was unchanged. Conclusions: GBP was associated with significant changes in body composition after six and twelve months. However, despite weight reduction, resting energy expenditure per fat free mass unit did not change significantly (Rev Méd Chile 2008; 136: 570-7). ( Key words: Energy metabolism; Gastric bypass; Obesity morbid) Recibido el 25 de enero, 2007. Aceptado el 17 de enero, 2008. Trabajo financiado por proyecto Fondecyt 1040765. 1 Departamento de Nutrición, Facultad de Medicina, Universidad de Chile. 2 Hospital Clíni- co Universidad de Chile. 3 INTA, Universidad de Chile. a Ph.D. b Nutricionista c Tecnólogo Médico A R T Í C U L O D E I N V E S T I G A C I Ó N