In one study, Dr. Frederick Samaha, from the Philadelphia Veterans Affairs Medical Center, and colleagues found that obese volunteers who consumed a low-carbohydrate diet for 6 months lost 5.8 kg, compared with only 1.9 kg for people on a low-fat diet (p = 0.002).
In a second study, obese people on a low-carbohydrate diet lost nearly 4% more body weight after 6 months than volunteers on a conventional diet, lead author Dr. Gary D. Foster, from the University of Pennsylvania in Philadelphia, and colleagues note.
However, by the end of the 1-year study period, the weight loss differences between the two groups had largely disappeared, suggesting that low-carbohydrate diets are no better than conventional diets at helping obese people lose weight.
"The average weight loss was greater in the low-carbohydrate groups than in the low-fat groups, but the difference was no longer significant at 12 months in the trial in which follow-up lasted that long," Dr. James Ware, from Harvard University in Boston, wrote in a related editorial.
Dr. Ware also noted that the weight lost in each study was relatively small compared with the volunteers' size. The average starting weight among the volunteers in the first study was about 130 kg. The baseline weight of subjects in the second study was about 98 kg.
In the United States, about 45% of women and 30% of men are on a diet. More than 60% of Americans are overweight and more than 30% are obese.
Low-carbohydrate diets have been criticized because their high fat content may increase the risk of heart disease, kidney problems and cancer.
Findings from the 12-month study indicate, however, that triglyceride levels fell further and HDL cholesterol levels rose higher with the low-carbohydrate diet than with the low-fat diet.
Still, Dr. Samaha's team notes that further "studies evaluating long-term cardiovascular outcomes are needed before a carbohydrate-restricted diet can be endorsed."
Referrence: N Engl J Med 2003;348:2074-2090