Both diets in the randomized, double-blind feeding trial carried a severe 30% calorie restriction, but both also followed current recommendations for healthy eating. The high-GI/high-carb diet was 60% carbohydrates, 20% protein, and 20% fat. The low-GI/low-carb diet was 40% carbohydrates, 30% protein, and 30% fat.

"If people consume a healthy diet that is calorie restricted, they are going to lose weight, and the quality of the carbohydrates doesn't really matter," said investigator Anastassios G. Pittas, MD, from Tufts–New England Medical Center in Boston, Massachusetts.

Dr. Pittas suggested in an interview that one reason analyses of the 12-month trial has not turned up any contrasts in outcomes so far between the two groups may have been because both diets reduced calories so much that subtle differences were lost.

He described an arduous regimen for the 34 overweight participants who were drawn from a large pool of volunteers in the Greater Boston area. About three quarters in both groups were women with an average age in the mid-30s and an average body mass index (BMI) at baseline of 27.6 kg/m2.

A metabolic kitchen at Tufts prepared all the meals, according to Dr. Pittas. Menus included microwavable entrees as well as salads. Patients picked up their diets every three days and were not supposed to eat anything outside of the trial.

Outcomes for the patients showed about a 10% reduction in BMI and a more than 20% increase in insulin sensitivity for both groups, according to Dr. Pappas. He said the investigators initiated the study because of concern that a carbohydrate-heavy diet with a high glycemic load could contribute to diabetes and insulin resistance.

Michael A. Hamilton, MD, MPH, former medical director of the Diet and Fitness Center at Duke University in Durham, North Carolina, said the study did not clear up confusion over high-GI and low-GI diets.

"There's nothing wrong with the study," Dr. Hamilton said. But "what do you do with this information, and what do you tell your patients? In the end what you tell your patients is to eat food in moderation and to exercise or to be more active physically," he said.

Source: Diabetes In Control.com: NAASO 2004 Annual Scientific Meeting: Abstract 40-OR. Presented Nov. 16, 2004.