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

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 F 9 years, with a body mass index of 51 F 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 F 23 kg vs 121 F 21 kg, P b .05), waist (136 F 17 cm vs 123 F 17 cm, P b .05), and hip circumference (149 F 14 cm vs 137 F 16 cm, P b .05) occurred during the study. Mean RMR measured by indirect calorimetry (10.6 F 1.7 MJ/d; 2540 F 420 kcal/d) was 16% higher (P b .05) than that calculated by HarrisBenedict and World Health Organization equations (8.7 F 0.9 MJ/d; 2070 F 210 kcal/d and 9.0 F 1.4 MJ/d; 2161 F 344 kcal/d, respectively) at the beginning, but not at the end of the study. Lipid oxidation rate was 45% of RMR at the beginning of the study, reaching 59% at the end (P N .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 lowcalorie 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.