Level 1: Likely reliable evidence

The Dietary Intervention Randomized Controlled Trial (DIRECT) evaluated the long-term efficacy of three weight-loss diets in mostly male patients (N Engl J Med. 2008;359:229-241). Participants (N=322) were aged 40-65 years with BMI >27 or had type 2 diabetes or coronary artery disease. Each was randomly assigned to one of three diets for two years: the Mediterranean diet; the low-carbohydrate (<120 g/day), nonrestricted kilocalorie diet; or the American Heart Association low-fat diet. The Mediterranean and low-fat diets limited women to 1,500 kcal/day and men to 1,800 kcal/day.

Mean weight at baseline was 91.4 kg (201 lb). Mean weight loss at two years was 4.4 kg (9.7 lb) with the Mediterranean diet vs. 4.7 kg (10.3 lb) with the low-carbohydrate diet vs. 2.9 kg (6.4 lb) with the low-fat diet (P <.001 for low-fat diet vs. each other group). In the low-carbohydrate diet group, increases in HDL and decreases in total cholesterol-to-HDL ratio and triglycerides were significant compared with the low-fat diet.