The effect of protein intake on 24-h energy expenditure during energy restriction

OBJECTIVE: To investigate whether protein intake influences the decline in energy expenditure during energy restriction. DESIGN: Cross-over study of three diets of 4.2 MJ/d for 7 days: one diet with 36% energy as protein and two with 15% energy as protein, one high in carbohydrate and the other high in fat. SUBJECTS: Two men and six women aged 31-57 y, BMI 27.8-34.1 kg/m(2). MEASUREMENTS: 24-h energy expenditure (24-h EE), sleeping metabolic rate (SMR) and body weight on days 0 and 7 of each diet; 24-h urinary nitrogen excretion (24-h UN) on days 0-7 of each diet. RESULTS: 24-h EE and SMR declined on all three diets but the decrease was significantly less on the high protein diet than on the two low protein diets. Weight loss was similar on all three diets, 24-h UN was less than N intake on the high protein diet but greater than N intake on the two low protein diets, CONCLUSIONS: Maintaining protein intake reduces the decrease in energy expenditure during energy restriction.