Researchers in the USA conducted a 1-year, multicentre, controlled trial involving 63 obese men and women who were randomly assigned to either a low-carbohydrate, high-protein, high-fat (Atkins) diet or a low-calorie, high-carbohydrate, low-fat (conventional) diet. Professional contact was minimal to replicate the approach used by most dieters. Subjects on the low-carbohydrate diet had lost more weight than subjects on the conventional diet at 3 months and 6 months, but the difference at 12 months was not significant. After 3 months, no significant differences were found between the groups in total or low-density lipoprotein cholesterol concentrations. The increase in high-density lipoprotein cholesterol concentrations and the decrease in triglyceride concentrations were greater among subjects on the low-carbohydrate diet than among those on the conventional diet throughout most of the study. Both diets significantly decreased diastolic blood pressure and the insulin response to an oral glucose load. These results show that the low-carbohydrate diet produced a greater weight loss (absolute difference, approximately 4%) than did the conventional diet for the first 6 months, but the differences were not significant at 1 year. The low-carbohydrate diet was associated with a greater improvement in some risk factors for coronary heart disease. Adherence was poor and attrition was high in both groups.