Changes in LDL ('bad') cholesterol levels were not significant. In both studies, at six months, the low-carb group had lost more weight than the low-fat group, but at the end of the 12-month study, both the low-carb and low-fat groups had lost about the same amount of weight.
For one year, researchers at the Veterans Affairs Medical Center in Philadelphia followed 132 obese adults randomized into two groups. One restricted carbohydrate intake to less than 30 grams per day (low-carbohydrate diet); the other restricted caloric intake by 500 calories, with 30 percent of calories from fat (conventional diet). Eighty-three percent of the study group had diabetes or other risk factors for heart disease.
In the low-carb group, triglyceride levels decreased more and HDL ('good') cholesterol levels decreased less than in the low-fat group. (High levels of trigylcerides, a fat in the blood, are associated with heart disease.) People with diabetes on the low-carb diet had better control of blood sugar.
At the six-month mark, the low-carb group had lost more weight than the low-fat group, as reported in a previously published article. However, by the 12-month point, both groups had lost about the same amount of weight (11 to 19 pounds for the low-carb group and 7 to 19 pounds for the low-fat group). The low fat group continued to lose weight from 6 to 12 months, whereas the average weight in the low-carb group remained steady after 6 months.
This twelve-month study is the longest study comparing low-carb vs. low-fat diets using subjects who have a high prevalence of diabetes.
"Americans are overweight because we're eating too much food and ingesting too many calories," said Linda Stern, MD, the lead author of the study and an internist at the Philadelphia VA Medical Center.
"I think a low-carbohydrate diet is a good choice because much of our overeating has to do with consumption of too many carbohydrates," Stern said.
Stern said that she was impressed that the low-carbohydrate group lost the weight in the first six months of the twelve-month study and didn't gain it back, but she cautioned, "More research is needed to see if a low-carbohydrate diet remains safe and effective for the longer term."
The second article in the May 18, 2004, issue of Annals of Internal Medicine involved 120 overweight people followed for six months. Researchers from Duke University found that participants on the low-carb diet lost an average of 26 pounds, compared to an average of 14 pounds lost by those on the low-fat diet.
The low-carbohydrate group had more beneficial changes in blood triglyceride levels and HDL cholesterol levels than the low-fat diet group. In this study, the low-carb diet groups also received vitamins and other nutritional supplements.
Patient summaries, prepared by Annals of Internal Medicine staff to accompany each article, point out limitations of the studies: limited number of participants, a high drop-out rate in one, nutritional supplements given to one diet group, limited length of studies (six months and 12 months) and difficulty in ascertaining exact food intake because participants prepared and ate their meals at home.
"We can no longer dismiss very-low-carbohydrate diets," said Walter C. Willett, MD, DrPH of the Harvard School of Public Health, in an editorial accompanying the two articles.
"(W)e can encourage overweight patients to experiment with various methods for weight control, including reduced carbohydrate diets, as long as they emphasize healthy sources of fat and protein and incorporate regular physical activity. Patients should focus on finding ways to eat that they can maintain indefinitely rather than seeking diets that promote rapid weight loss," Willet said.