Untested alternative weight loss diets, such as very low carbohydrate diets, have unsubstantiated efficacy and the potential to adversely affect cardiovascular risk factors. Therefore, we designed a randomized, controlled trial to determine the effects of a very low carbohydrate diet on body composition and cardiovascular risk factors. Subjects were randomized to 6 months of either an ad libitum very low carbohydrate diet or a calorie-restricted diet with 30% of the calories as fat. Anthropometric and metabolic measures were assessed at baseline, 3 months, and 6 months. Fifty-three healthy, obese female volunteers (mean body mass index, 33.6±0.3 kg/m 2) were randomized; 42 (79%) completed the trial. Women on both diets reduced calorie consumption by comparable amounts at 3 and 6 months. The very low carbohydrate diet group lost more weight (8.5±1.0 vs. 3.9±1.0 kg; P< 0.001) and more body fat (4.8±0.67 vs. 2.0±0.75 kg; P< 0.01) than the low fat diet group. Mean levels of blood pressure, lipids, fasting glucose, and insulin were within normal ranges in both groups at baseline. Although all of these parameters improved over the course of the study, there were no differences observed between the two diet groups at 3 or 6 months. β-Hydroxybutyrate increased significantly in the very low carbohydrate group at 3 months (P= 0.001). Based on these data, a very low carbohydrate diet is more effective than a low fat diet for short-term weight loss and, over 6 months, is not associated with deleterious effects on important cardiovascular risk factors in healthy women.

THE INCIDENCE OF obesity in the United States has risen continuously over the last several decades, and the associated medical and economic costs to society are substantial (1–3). Despite considerable desire on the part of obese individuals to lose weight (4) and the clear health benefits of doing so (5), there are currently no proven, effective approaches for meaningful and long-term weight loss for most overweight individuals (2). Dietary strategies supported by the majority of physicians and dietitians, which emphasize restriction of fat intake, are associated with only modest weight loss and poor long-term compliance (6, 7). Given these difficulties and the popular demand for effective weight loss methods, it is not surprising that a number of diet plans have been developed outside the medical and nutritional mainstream that are marketed directly to the public as weight loss strategies.