Weight and Metabolic Outcomes After 2 Years on a Low-Carbohydrate Versus Low-Fat Diet

Abstract

Previous studies have demonstrated that low-carbohydrate diets achieve greater short-term (6 months) weight loss than low-fat diets. Longer-term (1 to 2 years) data have been inconsistent. Weight loss obtained with either diet is generally minimal. Some investigators have attributed this suboptimal weight loss to the uniform lack of inclusion in most studies of behavioral interventions to change lifestyle. This randomized, parallel-group, controlled trial compared the effects of 2-year treatment with either a low-carbohydrate or low-fat diet combined with a behavioral intervention program on body weight and several other clinical endpoints. Between 2003 and 2007, 307 adults at a mean age of 45.5 years (SD, 9.7 years) and mean body mass index of 36.1 kg/m2 (SD, 3.5 kg/m2) were enrolled. A total of 153 of the study subjects (group 1) were assigned to a low-carbohydrate diet, which limited carbohydrate intake to 20 g/d for 3 months; unrestricted consumption of fat and protein was allowed. Carbohydrate intake after the first 12 weeks was gradually increased (5 g/d per week) until the desired weight was reached. Group 2 was comprised of 154 participants who were assigned to receive a low-fat diet limiting energy intake to 1200 to 1800 kcal/d, with ≤30% of the calories from fat. All participants received comprehensive behavioral treatment. Weight loss and most secondary outcomes (serum lipoproteins, blood pressure, urinary ketones, and symptoms were assessed at 3, 6, 12, and 24 months. Secondary outcomes of bone mineral density and body composition were evaluated at 6, 12, and 24 months. Both diet groups achieved clinically significant and almost identical weight loss at 1 year (11 kg [11%]) and at 2 years (7 kg [7%]. No differences were found between the groups in weight, bone mineral density, or body composition over the 2 years of the study. At 3 and 6 months, however, significantly greater reductions were found in the low-carbohydrate diet group than in the low-fat diet group for triglyceride levels, diastolic pressure, and very-low-density as well as low-density lipoprotein cholesterol levels. More adverse symptoms were observed in the first 6 months in the low-carbohydrate diet group. An increase of approximately 20% in high-density lipoprotein cholesterol levels was observed in the low-carbohydrate diet group at 6 months and persisted throughout the study; this increase was more than twice that found in the low-fat diet group. The investigators conclude from these findings that either a low-carbohydrate or a low-fat diet can achieve successful long-term weight loss if combined with a behavioral intervention program.