A method to achieve control of dietary macronutrient composition in ad libitum diets consumed by free-living subjects

Abstract

Objective: To validate a shop system in controlling macronutrient composition during ad libitum dietary intervention. Design: Six months randomized intervention trial. Setting: A shop at the department from which all foods were collected free of charge and registered by a purpose-designed computer system. Subjects: Sixty-five free-living obese subjects (25 kg/m²<BMI<34 kg/m²) recruited through advertisement and from a waiting list at the Department. Total drop-out rate was 8%. Interventions: Ad libitum low-fat diets (30 energy-% (E%) fat): (1) High-protein (25 E% protein, HP) or (2) Low-protein, (12 E% protein, LP) or habitual diet (controls, C). Main outcome measures: Compliance was assessed by 24 h urinary nitrogen excretion (24 h UN). Results: After one month of dietary intervention 24 h UN increased significantly in the HP group and decreased significantly in the LP group (Group difference 95% CI):6.8 g (5.0–8.7 g), P<0.0001). This group difference remained throughout the trial. There was good agreement between protein intake as estimated by the shop computer and as estimated from 24 h UN in both first (r=0.86) and second half of the intervention (r=0.80). Conclusion: The high dietary compliance demonstrates the potential of this method to control macronutrient composition in ad libitum dietary intervention studies in free-living subjects. Sponsorship: This study was supported by The Federation of Danish Pig Producers and Slaughterhouse, Danish Dairy Research Foundation, The Danish Livestock and Meat Board and the Danish Research and Development Program for Food Technology 1990–1994.