Results at 1 year: low-carb, low-fat diets show similar weight loss.(Clinical Rounds)

New data show that after 1 year, low-carbohydrate dieters don't maintain the greater weight losses that they have at 6 months, compared with conventional low-fat, low-calorie dieters.

Results from a 1-year follow-up study by Dr. Linda Stern of the Philadelphia Veterans Affairs Medical Center and colleagues extended 6-month data reported by coauthor Dr. Frederick F. Samaha. The researchers followed patients who had been randomized to either a diet containing 30 g or less of carbohydrates per day or a conventional diet with less than 30% of total caloric intake from fat and a deficit of 500 calories per day (Ann. Intern. Med. 140[10]:778-85, 2004).

After 1 year, total weight loss was similar in the two groups. The mean weight loss was 5.1 kg among the 44 people in the low-carbohydrate group and 3.1 kg among the 43 people in the conventional-diet group, a non-significant difference.

Most of the weight loss in the low-carbohydrate group took place during the first 6 months of the diet; the results caught the public's attention when they were published (N. Engl. J. Med. 348[21]:2074-81, 2003). But the weight-loss differences between the two groups were not significantly different between 6 months and 1 year. Participants in the low-carbohydrate group who dropped out of the study lost less weight than those who completed it. Those in the conventional-diet group lost about the same amount of weight whether they dropped out or completed the study.

Triglycerides decreased significantly in the low-carbohydrate group, compared with the conventional-diet group. Decreases were associated with assignment to the low-carbohydrate group and greater weight loss during the study.

One person in the low-carbohydrate group was hospitalized for noncardiac chest pain during the third month of the study. Also, two people in the low-carbohydrate group died, one of complications from hyperosmolar coma at 5 months into the study and one of sudden severe ischemic cardiomyopathy at 10 months into the study. Laboratory analysis 14 days prior to the cardiomyopathy patient's death showed no abnormalities in electrolytes.

The two most important limitations of the study were the high dropout rate and the fact that most people did not consistently meet the daily dietary goals of consuming less than 30 g of carbohydrates or consuming 500 fewer calories. Only 44 of 64 people in the low-carbohydrate group and 43 of 68 people in the conventional-diet group completed the study.