Two Year Study: Low-carbohydrate vs. Low-fat Diets

In most previous studies of low-carbohydrate versus low-fat diets, investigators have focused on short-term weight-loss results. U.S. researchers now report results of a 2-year study in which 307 adults (mean body-mass index, 36 kg/m²) were randomized to a low-carbohydrate diet that allowed unrestricted consumption of fat or to a low-fat diet with approximately 30% of calories from fat. All participants received additional behavioral interventions, including self-monitoring and physical activity sessions. People with diabetes or hyperlipidemia were excluded.

In both groups, mean weight loss was approximately 11 kg at 1 year and 7 kg at 2 years. No significant between-group differences at 2 years were noted in mean triglyceride levels, LDL cholesterol levels, and total cholesterol/HDL cholesterol ratio; however, mean HDL cholesterol levels were significantly higher in the low-carbohydrate group (absolute difference, approximately 2 mg/dL). Attrition was approximately 50% at 2 years.

Half the participants in this long-term randomized study dropped out, a figure that underscores the difficulty of weight loss. These results support the findings of previous studies that have shown that patients can choose either a low-fat or low-carbohydrate diet and expect similar results. Mean weight loss was 7 kg at 2 years with either type of diet.

Foster GD et al. Weight and metabolic outcomes after 2 years on a low-carbohydrate versus low-fat diet: A randomized trial. Ann Intern Med 2010 Aug 3; 153:147.