The average weight of the women in this study was 200 pounds at the beginning. The women followed either a very low-carbohydrate diet or a calorie-restricted diet with 30% of calories derived from fat. Food consumption was assessed through self-reported diaries, and the researchers concluded that the low-fat dieters averaged 1,500 to 1,700 calories a day, while the low-carb dieters ate 1,600 to 1,800 calories a day. The findings are reported in the April issue of the Journal of Clinical Endocrinology and Metabolism.
In both diet groups, much of the total weight loss occurred within the first few weeks and there was very little weight loss during the last three months. Brehm says loss of water weight probably explains the former finding, and poor compliance with the diets may explain the latter. For the first three months the women in the study were monitored very closely, but for the last three months they weren't monitored at all.
"This study shows that a low-carbohydrate diet is effective in the short term in healthy overweight people, but it is important that we look at the long-term effectiveness of this diet and whether it is safe for people who are at risk for cardiovascular disease," she says.
American Dietetic Association spokeswoman Kathleen Tallmadge, RD, says short-term studies like this one and last summer's Duke findings prove little about the safety and long-term effectiveness of carbohydrate-restricted diets. She adds that it should come as no surprise that people who lost weight on these diets saw improvements in heart-disease risk, because that is what happens when people lose weight.
"The problem is when the weight loss stops, cholesterol and other cardiovascular risks are likely to skyrocket in people on low-carbohydrate diets that are high in saturated animal fats," Tallmadge tells WebMD. "The best way to lose weight permanently is to adopt a way of eating that can be maintained for a lifetime, and that is not possible with these very restricted diets."
She says it is good for everyone to limit their intake of sugar and white flour, but adds that the low-carb diet restrictions on fruits, vegetables, and whole grains make no nutritional sense.