A Randomized Trial of Energy-Restricted High-Protein Versus High-Carbohydrate, Low-Fat Diet in Morbid Obesity

Objective: Conflicting evidence exists as to weight loss produced by diets with different carbohydrate/protein ratio. The aim was to compare the long-term effects of high-protein vs. high-carbohydrate diet (HPD, HCD), combined with cognitive behavior therapy (CBT). Design and Methods: In a randomized trial, 88 obese participants (mean age, 46.7; mean BMI, 45.6 kg m(-2)) were enrolled in a 3-week inpatient and 48-week outpatient treatment, with continuous CBT during the study period. All subjects consumed a restricted diet (1,200 kcal day(-1) for women, 1,500 for men; 20% energy from fat, <10% saturated fat). HPD derived 34% energy from proteins, 46% from carbohydrates; HCD 17% from proteins, 64% from carbohydrates. The primary outcome was 1-year percent weight loss. Secondary outcomes were attrition rates and changes in cardiovascular risk factors and psychological profile. Results: Attrition rates were similar between groups (25.6%). In the intention-to-treat analysis, weight loss averaged 15.0% in HPD and 13.3% in HCD at 1 year, without any difference throughout the study period. Both diets produced a similar improvement in secondary outcomes. Conclusions: The relative carbohydrate and protein content of the diet, when combined with intensive CBT, does not significantly affect attrition rate, weight loss and psychosocial outcome in patients with severe obesity.