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Synopsis: The low-carbohydrate diet produced a greater weight loss than did the conventional diet for the first 6 months, but the differences were not significant at 1 year.
Sources: Samaha F, et al. N Engl J Med. 2003;348:2074-2081; Foster GD, et al. N Engl J Med. 2003;348:2082-2089.
The marked increase in the number of people who are obese and the alarming increase in the incidence of type 2 diabetes have resulted in an amazing number of new books on diet. A great deal of controversy has arisen over the benefits of a low-carbohydrate, high-protein diet. The Atkins diet in particular has received much attention despite limited long-term controlled studies relating to its benefit.
Two recent studies examining the benefits of a high- protein, high-fat, low-carbohydrate diet vs a high-protein, low-fat, high-carbohydrate diet, appeared in the same issue of the New England Journal of Medicine.
Bonow and Eckel succinctly summarized these studies in their accompanying editorial.1 "Each group of investigators randomly assigned obese subjects to either a low-carbohydrate diet (with high protein and fat content) or a more standard, reduced-fat diet (with fat constituting less than 30 % of the total caloric intake but more than in some extremely low-fat diets). Each study was designed to follow subjects for more than 90 days. Samahah and colleagues followed severely obese subjects (mean body-mass index, 43) with a high prevalence of diabetes (39%) or of the metabolic syndrome without diabetes (43%), whereas Foster and associates studied subjects with less severe obesity (mean body-mass index, 34), none whom had diabetes. Samaha et al used fixed-carbohydrate restriction (30 g or less per day), and Foster et al used the Atkins diet.
Despite these differences in study population and dietary approaches, both studies demonstrated significantly greater weight reduction with the low-carbohydrate diet than with the reduced-fat diet during the first 6 months (average reduction, 6 to 7 kg vs 2 to 3 kg); however, the magnitude of the weight loss difference (4 kg in both studies) was relatively small and adherence in the 2 diet groups was low. In addition, in the study by Foster et al, there was no longer a significant difference in the weight loss between the subjects in the low-carbohydrate group and those in the reduced-fat group at 12 months.
Comment by Ralph R. Hall, MD, FACP
The dropout rate in both studies was significant—53 of 132 patients in the Samaha et al group and 24 of 63 patients in the Foster et al group. The patients who dropped out were not followed in order to determine their ultimate weight loss or gain. Some studies have shown that a number of subjects who drop from a study continue to follow the diet and lose weight.
The subjects on the low-carbohydrate diet, in both groups, had a reduction in risk factors for coronary heart disease, ie, drops in triglycerides and insulin resistance, and the Foster et al group had a rise in the high density cholesterol level. Subjects on the low-fat diet had a drop in their LDL cholesterol.
Another important diet study which Eckel, one of the authors of the editorial, was involved, was just reported at the American Diabetes Association meeting.2 Cornier and Eckel examined insulin-sensitive (IS) and insulin-resistant (IR) female obese subjects’ response to both a high-carbohydrate, low-fat (HC/LF) and a low-carbohydrate, high-fat diet (LC/HF), (400 kg/d deficit). The study lasted 16 weeks. IR women in the HC/LF diet lost a significantly greater amount of weight than those randomized to the LC/HF diet (11.47 kg vs 6.12 kg; P < 0.01). IR women randomized to the LC/HF lost significantly more weight than those randomized to the HC/LF diet (11.46 kg vs 6.12 kg; P = 0.05).
Triglycerides decreased significantly in all groups except the IR women on the HC/LF diet. In summary, obese IS women lose more weight on a diet that is low in fat content, while IR women lose more weight on a diet that is low in carbohydrate and high in fat. Insulin sensitivity was determined by a fasting, blood insulin.
The marked differences in weight loss when women, and likely men, are given a diet matched to their insulin sensitivity has great potential. The remaining problem is how long can we keep patients on a high-fat diet without increasing the risk of vascular disease? The ill effects of long-term, high-fat diet have been repeatedly demonstrated. The paucity of fruits and vegetables in the high- fat diet removes nutrients that have long been demonstrated to have significant health benefits.
1. Bonow R, Eckel R. N Engl J Med. 2003;348:2057-2058.
2. Cornier MA, et al. 2003 American Diabetes Association Meeting, Abstract 313.