Staying away from simple carbohydrates and eating plenty of fiber may help women avoid packing on pounds as they get older, a study by Danish researchers suggests.

Dr. Helle Hare-Bruun of Copenhagen University Hospital and colleagues found that normal-weight women who ate a diet with a relatively high glycemic index gained more weight, more fat, and more padding around the middle over a six-year period than women who ate a low glycemic index diet.

But larger, longer-term studies are needed to show how a low glycemic index diet affects weight regulation, Dr. Mark A. Pereira of the University of Minnesota in Minneapolis writes in an accompanying editorial.

Glycemic index is a measure of how quickly a food causes blood sugar, or “glucose,” to rise. Generally, foods with refined sugars and simple starches, like candy and white bread, have a high glycemic index, while those with more complex carbohydrates and greater fiber content, such as vegetables and whole grains, have a low glycemic index.

Theoretically, a high glycemic index diet could make a person feel hungry faster and eat too much as a result, Hare-Bruun and colleagues note. But studies of the effects of dietary glycemic index on weight loss have had mixed results, they report in the American Journal of Clinical Nutrition.

To see how dietary glycemic index might affect weight over time, the researchers evaluated 376 normal-weight men and women ages 35 to 65 years and followed-up with them six years later.

As mentioned, a high glycemic index diet correlated with greater waist circumference, body weight, and percentage of body fat in women, the researchers found, and the effect was strongest among inactive women. But glycemic index had none of these effects on men. The researchers suggest that gender somehow affects the influence of glycemic index on weight gain.

“A low glycemic index diet may protect against increases in body weight and general and abdominal obesity in women - especially in those who are sedentary - which suggests that physical activity may offer protection against diet-induced weight gain and obesity,” they conclude.

But given the relatively small size of the current study and the difficulty of accurately evaluating diet from self-reports, Pereira writes in his editorial, much larger, long-term trials are needed to answer the question of how dietary glycemic index affects body weight.

SOURCE: American Journal of Clinical Nutrition, October 1, 2006.