Six-Month Study Shows Low-Carb Diet Is More Effective Than Low-Fat Diet

News Author: Laurie Barclay,
MD CME
Author: Bernard M. Sklar,
MD, MS

April 29, 2003 — Women eating ad lib on a low-carbohydrate diet lost more weight than those on a calorie-restricted low-fat diet even though the calorie load was similar, according to the results of a randomized trial published in the April issue of the Journal of Clinical Endocrinology and Metabolism. There were no adverse effects from either diet during the six-month study period.

"Untested alternative weight loss diets, such as very low carbohydrate diets, have unsubstantiated efficacy and the potential to adversely affect cardiovascular risk factors,"write Bonnie J. Brehm, PhD, and colleagues from the University of Cincinnati and Children's Hospital Medical Center in Ohio.

Of 53 healthy obese female volunteers (mean body mass index, 33.6 ± 0.3 kg/m2), who were randomized to six months of either an ad libitum very low carbohydrate diet or a calorie-restricted diet with 30% of the calories as fat, 42 women (79%) completed the trial.

Both groups reduced caloric intake by comparable amounts at three and six months. Compared with the low-fat diet group, the low-carbohydrate diet group lost more weight (8.5 ± 1.0 vs. 3.9 ± 1.0 kg; P < .001) and more body fat (4.8 ± 0.67 vs. 2.0 ± 0.75 kg; P < .01).

(Michael's note: this means that the low carbohydrate diet group lost over twice as much bodyfat as the low fat diet. 4.8 pounds versus 2 pounds.)

Mean levels of blood pressure, lipids, fasting glucose, and insulin were within normal ranges in both groups at baseline and improved during the study, but there were no differences between the two groups at three or six months. Beta-hydroxybutyrate increased significantly in the low-carbohydrate group at three months (P = .001).

The authors warn that these results should not be extrapolated to subjects with cardiovascular risk factors at baseline, and that longer studies are needed. This study suggested some recidivism during the last three months, and low calcium and fiber intake could prove to be problematic over longer periods.

"Based on these data, a very low carbohydrate diet is more effective than a low fat diet for short-term weight loss and, over 6 months, is not associated with deleterious effects on important cardiovascular risk factors in healthy women," the authors write. "There are important, interesting, and poorly understood effects of severe carbohydrate restriction that warrant further investigation as we seek effective therapeutic strategies to manage the epidemic of obesity."

J Clin Endocrinol Metab. 2003;88:1617-1623