A low-calorie diet improves the rate of nutrient oxidation, lowers body fat, and maintains lean mass in morbidly obese Brazilian women

Abstract To assess the effect of a low calorie diet on the resting metabolic rate (RMR), substrate oxidation, body composition, and to compare measured and calculated RMR of obese Brazilian women, we selected 19 patients aged 31 ± 9 years, with a body mass index of 51 ± 8 kg/m 2 , for admission to the Metabolic Unit of the University Hospital for 8 weeks, who were then submitted to a 3.3 to 4.2 MJ/d (800-1000 kcal/d) diet. Weight, height, and circumferences were measured on the first and last days of the study. Body composition was assessed by bioelectrical impedance, and RMR and substrate oxidation rate by indirect calorimetry. A decrease in body weight (134 ± 23 kg vs 121 ± 21 kg, P P P P P > .05). Present data suggest that equations to estimate RMR of obese females are reliable after a low-calorie diet and weight loss. Resting metabolic rate was correlated with fat-free mass and body fat. A low-calorie diet with balanced macronutrients is effective for weight loss, leading to a maintenance of lipid oxidation rate and to a reduction of carbohydrate and protein oxidation rates. The low-calorie diet reduced body fat and maintained lean mass.