Despite the popularity of the low-carbohydrate, high-protein, high-fat diet, no randomized, controlled trials have evaluated its efficacy. The conventional dietary approach to weight management, recommended by the leading research and medical societies, is a high-carbohydrate, low-fat, energy-deficit diet. The Atkins diet, originally published in 1973 and again in 1992 and 2002, may be the most popular of the low carbohydrate diets. More than 10 million copies of Atkins’s diet book have been sold, and four times as many dieters have read one of the Atkins books as have read any other diet book. Despite its longevity and popularity, no randomized trials evaluating the efficacy of the Atkins diet have been published.

The researchers of the current study conducted a one-year, multicenter, randomized, controlled trial to evaluate the effect of the low-carbohydrate, high-protein, high-fat Atkins diet on weight loss and risk factors for coronary heart disease in obese persons. The subjects were randomly assigned to follow either a low-carbohydrate, high-protein, high-fat Atkins diet or a high-carbohydrate, low-fat, energy-deficit conventional diet. Professional contact was minimal, so as to approximate the approaches used by most dieters.

A total of 63 persons (43 women and 20 men) participated in the study. All subjects completed a comprehensive medical examination and routine blood tests. Subjects in both test groups were instructed to take a daily multivitamin supplement and met with a registered dietitian for 15 to 30 min during the third, sixth, and twelfth months to review dietary issues.

The 33 subjects who were assigned to the low-carbohydrate, high-protein, high-fat diet met individually with a registered dietitian before beginning the program to review the central features of the diet, which involves limiting carbohydrate intake without restricting consumption of fat and protein intake. For the first two weeks, carbohydrate intake is limited to 20 g per day and is then gradually increased until a stable and desired weight is achieved. Each subject was given a copy of Dr. Atkins’ New Diet Revolution.

The 30 subjects who were assigned to the conventional diet also met with a registered dietitian before beginning the program to review the components of a high-carbohydrate, low-fat, low-calorie diet (1200 to 1500 cal per day for women and 1500 to 1800 cal per day for men, with approximately 60% of cal from carbohydrate, 25% from fat, and 15% from protein) and to receive instructions about calorie counting. Subjects were given a copy of the Learn Program for Weight Management, which provides 16 lessons covering various aspects of weight control.

A total of 49 subjects completed three months of the study (28 on the low-carbohydrate diet and 21 on the conventional diet), 42 subjects completed six months (24 on the low-carbohydrate diet and 18 on the conventional diet), and 37 subjects completed twelve months (20 on the low-carbohydrate diet and 17 on the conventional diet). The percentage of subjects who had dropped out of the study during the third, sixth, and twelfth months was higher in the group following the conventional diet, but the difference was not statistically significant. Subjects on the low-carbohydrate diet lost significantly more weight than did the subjects on the conventional diet during the third and the sixth months, but the difference in weight loss was not statistically significant at during the twelfth month. During the first three months, the percentage of patients who tested positive for urinary ketones was significantly greater in the group on the low-carbohydrate diet than was in the group on the conventional diet, but there was no significant difference between the groups after three months. Systolic blood pressure did not change significantly in either group during the study. Diastolic blood pressure decreased in both groups, but there was no significant difference between the groups. The area under the glucose curve did not change significantly during the oral glucose-tolerance test throughout the study. The area under the insulin curve decreased in both groups, without significant difference between the groups.

There were no significant differences between groups in the total or LDL cholesterol concentration, except on the third month, when values were significantly lower in the group on the conventional diet than in the group on the low-carbohydrate diet. In contrast, the relative increase in HDL cholesterol concentrations and the relative decrease in triglyceride concentrations were greater in the group on the low-carbohydrate diet than in the group on the conventional diet throughout most of the study.

The results of this multicenter, randomized, controlled trial demonstrate that the low-carbohydrate, high-protein, high-fat Atkins diet produces greater weight loss (an absolute difference of approximately 4%) than a conventional high-carbohydrate, low-fat diet for up to six months, but that the differences do not persist at one year. These data suggest that long-term adherence to the low-carbohydrate Atkins diet may be difficult. The differences in weight loss between the two groups in the first six months demonstrate an overall greater energy deficit in the low-carbohydrate group. The mechanism responsible for the decreased energy intake induced by a low-carbohydrate diet with unrestricted protein and fat intake is not known, but may be related to the monotony or simplicity of the diet, alterations in satiety factors, or other factors that affect appetite and dietary adherence.