Despite the fact that more than one third of adults in the United States claim to be dieting at any given time, the incidence of obesity has doubled in the past two decades. Traditional dieting schemes have relied on low-fat, high-carbohydrate regimens to limit caloric intake. The Atkins-type diets that recently have become popular reverse this scheme by restricting carbohydrate intake and allowing high-fat consumption within an overall calorie restriction. Foster and associates conducted a randomized, one-year trial to evaluate the efficacy of a low-carbohydrate, high-protein, high-fat Atkins-type diet on weight loss and risk factors for coronary heart disease.
The study authors enrolled a total of 63 subjects (43 women and 20 men). There was no description as to how these persons were referred or recruited to the trial. Exclusion criteria included any current use of weight-loss or lipid-lowering medications, and type II diabetes, pregnancy, or lactation. To replicate the conditions under which most persons diet, the study design provided for only limited formal dietary instruction during participation. Participants were randomly assigned to follow either the low-carbohydrate, Atkins-type diet (33 participants) or the conventional diet (30 participants). Before beginning their diet program, subjects met with a registered dietitian to review their dietary assignment, and received either Dr. Atkins' low-carbohydrate diet book or a text that outlined a traditional low-fat diet approach, depending on their study assignment. Participants were assessed at baseline and 10 times during the year of the trial for body weight, blood pressure, and blood tests, but did not receive further individualized diet counseling.
As with most diet trials, the drop-out rate was substantial, with only 37 subjects completing the full 12 months. By the end of the one-year trial, 39 percent of participants on the Atkins-type diet had dropped out compared with 43 percent of those on the conventional diet.
Participants on the Atkins-type diet lost significantly more weight than those on the conventional diet at three months and six months, but there was no statistically significant difference in the average amount of weight loss after one year. There also were no significant differences between the two groups in blood pressure, total serum cholesterol level, glucose tolerance test results, or insulin sensitivity. Significant differences did persist after one year in a relative decrease in triglyceride concentrations and an increase in high-density lipoprotein cholesterol concentrations, which were greater in persons following the Atkins-type diet.
The authors conclude that the Atkins-type, low-carbohydrate diet does not significantly improve weight loss after one year compared with a traditional low-fat diet regimen. It also does not improve most obesity-related health parameters.