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A method to achieve control of dietary macronutrient composition in ad libitum diets consumed by free-living subjects
1Research Department of Human Nutrition, Royal Verterinary and Agricultural University, Frederiksberg, Copenhagen, Denmark.
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.
