LOS ANGELES – A low-carbohydrate diet produced greater weight loss than did a low-fat diet and reduced systemic inflammation to a similar extent, according to results from a 6-month randomized trial.
The finding that both types of weight-loss diets produced similar reductions in inflammatory markers should help put to rest the concern that a low-carbohydrate diet’s higher fat content might have a negative impact on cardiovascular health, explained Kerry J. Stewart, Ed.D., at the annual scientific sessions of the American Heart Association.
Dr. Kerry J. Stewart
"The concern about the low-carbohydrate diet is coming from the biomedical community. That’s why we did this study, to challenge that whole bias against this approach," explained Dr. Stewart, professor of cardiology and director of clinical research on exercise physiology at Johns Hopkins University, Baltimore.
"We’ve been told for the last 30-40 years, especially by the AHA and other groups, that high fat in the diet raises cholesterol and that all the other things that go along with that have harmful effects on the vasculature," he noted. "But we’ve previously shown no adverse effects on endothelial function or vascular stiffness, [as well as] significant improvements in blood pressure and cholesterol levels, with a low-carbohydrate diet."
Dr. Stewart reported on 60 middle-age overweight or obese patients who participated in a lifestyle intervention consisting of an exercise program plus randomization to a low-fat diet or an isocaloric low-carbohydrate diet.
From a mean baseline body weight of 97.1 kg, patients in the low-carbohydrate-diet group lost an average of 13.1 kg over 6 months, compared with 8.2 kg in the patients on the low-fat diet. From a mean baseline of 43.3%, total body fat dropped by an absolute 6.8% in the low-carb group, a significantly better result than the 4.0% decrease in the low-fat group. From a baseline mean body mass index of 34.2 kg/m2, BMI improved by 4.7 kg/m2 in the low-carbohydrate diet group, compared with 2.9 kg/m2 with the low-fat diet.
High-sensitivity C-reactive protein levels fell by a mean of 1.8 mg/L in both groups, from 5.2 mg/L at baseline. The other markers of systemic inflammation measured in the study – levels of interleukin-6 and tumor necrosis factor-alpha – also improved to a similar degree in both study arms.
"It’s important to keep in mind that this was a weight-loss study. If someone is normal- or underweight and eats this kind of low-carbohydrate diet, I’m not exactly sure what would happen," Dr. Stewart observed. "But in the context of a weight-loss program, it seems like the weight loss is an overwhelming benefit that overcomes any possible risks from eating more fat."
One audience member who had helped run a study of an Atkins-type low-carb/high-fat diet said he and his coinvestigators found deleterious effects on arterial flow-mediated dilation over the course of a year. But Dr. Stewart was unconvinced.
"We’ve looked at that literature. It’s a real mixed bag. Some studies show just what you say, others show just the opposite," he replied. "It’s very hard to draw any conclusions from these feeding studies. We’ve done some of them ourselves and found just the opposite of what you said."
Also, as another audience member pointed out, the low-carbohydrate diet employed in this study wasn’t an Atkins-type diet that’s high in total and saturated fat. Dr. Stewart agreed. "The patients really didn’t eat more fat, compared to the typical American diet," he noted.
Indeed, the roughly 1,700 Kcal/day low-carbohydrate diet consisted of 28% of energy from carbohydrates, 29% from protein, and 39% from fat. The isocaloric low-fat diet was 49% carbohydrate, 21% protein, and 29% fat.
Dr. Stewart reported having no financial conflicts.