April 15, 2003 -- There is new evidence that the popular but highly criticized very low-carbohydrate diets work and don't increase heart-disease risk factors -- at least in the short term.
In one of the first studies comparing low-fat and very low-carb approaches to weight loss, otherwise healthy obese women on carbohydrate restricted diets lost more than twice as much weight and significantly more body fat as women on a diet that restricted fat, even though both groups reported eating a similar number of calories each day.
Women eating the very low-carbohydrate diet lost an average of almost 19 pounds during the six-month study, compared with a loss of 8.5 pounds among the women eating a low-fat diet. Both groups saw improvements in blood pressure, cholesterol, and blood sugar and insulin levels.
Lead researcher Bonnie J. Brehm, PhD, RD, cautions that her short-term study, which included just 42 women, is far from the definitive word on whether a very low-carbohydrate diet is safe. But she says it is likely to spur more research into the diet made popular decades ago by the now famous diet guru Robert Atkins, MD.
"This study really produced more questions than answers," she says. "We don't know why the low-carb dieters lost so much more weight. We have no reason to believe that one group underreported their food consumption any more than another, and they reported eating about the same number of calories."
All the women participating in the study were told to maintain their pre-diet levels of exercise. But Brehm says the low-carb, high-protein dieters may have increased their activity levels without realizing it. Atkins proponents claim that people on the diet burn fat more quickly because carbohydrate restriction speeds up the metabolism. But Brehm, a University of Cincinnati dietitian, says there is little scientific evidence to back up the claim.
After decades of medical ridicule, the Atkins weight loss approach gained some credibility last summer with the release of widely publicized research from Duke University. Dieters in the Atkins-funded study lost an average of 20 pounds in six months, and also saw improvements in cholesterol and other cardiovascular risk factors.
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.
"When people start to fear whole food groups, no matter what they are, they are setting themselves up for an eating disorder" she says. "Successful dieters develop habits that they can maintain over a lifetime. Simple changes can really make a difference."