21 Jun 2010 --- Obese women with insulin resistance lose more weight after three months on a lower-carbohydrate diet than on a traditional low-fat diet with the same number of calories, according to a new study. The results will be presented Saturday at The Endocrine Society's 92nd Annual Meeting in San Diego.

"The typical diet that physicians recommend for weight loss is a low-fat diet," said the study's lead author, Raymond Plodkowski, MD, chief of endocrinology, nutrition and metabolism at the University of Nevada School of Medicine, Reno. "However, as this study shows, not all people have the same response to diets."

People with insulin resistance, a common precursor for Type 2 diabetes, metabolize carbohydrates, or "carbs," abnormally, which may affect their rate of weight loss. For them, Plodkowski said, "the lower-carb diet is more effective, at least in the short term."

At 12-weeks, the study funded by Jenny Craig and using prepared calorie-controlled meals as part of a behavioral weight loss program, found that the insulin resistant women on a lower-carb diet lost 3.4 pounds more than those on a low-fat diet.

Forty-five obese women between the ages of 18 and 65 years participated in the study, and all had insulin resistance, as found by fasting blood levels of insulin. The researchers randomly assigned the women to either a low-fat or lower-carb diet. The groups did not differ significantly in average body weight, the authors reported. On average, women in the low-fat diet group weighed 213 pounds, while women in the other group weighed 223 pounds.

The composition of the low-fat diet was 60 percent of calories from carbs, 20 percent from fat and 20 percent from protein. Although the lower-carb diet also had 20 percent of calories from protein, it had 45 percent from carbs and 35 percent from primarily unsaturated fats, such as nuts. Menus included a minimum of 2 fruits and 3 vegetable servings a day.

Use of prepared meals helped make the structured diets easier and more palatable for the dieters, according to Plodkowski. "We wanted to make this study real-world—anyone could follow this plan by making moderate changes as part of a healthy menu," he said.

Both groups lost weight at each monthly weigh-in, but by 12 weeks, the insulin resistant group receiving the lower-carb diet lost significantly more weight, 19.6 pounds versus 16.2 pounds in the low-fat diet group – approximately 21 percent more on average.

"These data have potential widespread applications for clinicians when counseling people with insulin resistance to help improve weight loss as part of a calorie-restricted diet," Plodkowski said. "They should at least initially lower their carbohydrate intake."