Objective: We investigated the effect of hypocaloric mixed diets with different proportions of carbohydrate, protein, and fat on resting metabolic rate and the thermic effect of food in obese women.
Methods: Three mixed hypocaloric diets were consumed in random order during separate periods lasting 7 d each. Between each dietary period there was a washout period of 10 d. Diet 1 had a higher proportion of energy from carbohydrate (72%), diet 2 had a higher proportion of energy from protein (43%), and diet 3 had a higher proportion of energy from fat (68%). Indirect calorimetry and lung function tests were done after the completion of each 7-d diet. Seven obese women, ages 22 to 45 y and with body mass indexes of 32 to 59 kg/m(2), participated in the study. Oxygen consumption, carbon dioxide production, resting metabolic rate, and the thermic effect of food by indirect calorimetry were measured. Lung function tests included spirometry in the seated and upright positions, arterial blood gas analysis, and maximal inspiratory and expiratory pressures.
Results: There were no statistically significant differences in the resting metabolic rate and the thermic effect of food resulting from the three diets. The mean resting metabolic rates (kJ/d) were 7453 +/- 1446 for diet 1, 7461 +/- 1965 for diet 2, and 7076 +/- 2048 for diet 3. The mean thermic effects of food (kcal/min) were -0.02 +/- 0.07 for diet 1, -0.01 +/- 0.25 for diet 2, and 0.05 +/- 0.13 for diet 3. Lung function tests were normal before and after the hypocaloic diets: partial pressure of oxygen (mmHg) values were 81 +/- 13, 77 +/- 8, and 78 +/- 11 for diets 1 to 3, respectively; and partial pressure of carbon dioxide (mmHg) were 37 +/- 4, 37 +/- 3, and 37 +/- 4 for diets 1 to 3, respectively.
Conclusions: Obese women with normal lung function tests and consuming mixed hypocaloric diets showed no alteration in resting metabolic rate and a reduced or absent thermic effect of food independently of the macronutrient composition.