NEW YORK (Reuters Health) – By itself, maintaining a low-fat diet does not appear to reduce the likelihood that postmenopausal women will develop diabetes, according to a study published Monday. However, among women on a low-fat diet who lost weight over the 8-year study, fewer of them developed diabetes, the researchers report.

“Weight loss, rather than nutrient composition, may be the dominant predictor of reduced risk of diabetes,” the investigators conclude in the Archives of Internal Medicine.

Dr. Lesley F. Tinker at the Fred Hutchinson Cancer Research Center in Seattle and colleagues looked at the effects of eating a low-fat diet on diabetes risk in over 48,000 women ages 50 to 79 years who were free of diabetes when they entered the Women’s Health Initiative Dietary Modification Trial.

The women were randomly assigned to continue eating their usual diet (the control group), or to go on to a low-fat diet (20 percent of calories from fat) with increased amounts of fruits, vegetables and whole grains, during the study period from 1993 to 2005.

The diet was not intended to help participants lose weight, and neither the diet group nor the control group was given goals for weight loss or physical activity.

By the end of the study, diabetes developed in 7.1 percent of women on the low-fat diet and 7.4 percent of those in the control group — not a significant difference from a statistical standpoint.

However, among women on the low-fat diet, the investigators found there was a trend toward greater reduction in diabetes risk with greater decreases in total fat intake and weight loss. Further analysis showed that most of this effect was attributable to weight loss.

Women in the low-fat diet group lost about 1.9 kilograms or 4.2 pounds more weight over the course of the study than women in the control group.

In a related commentary published with the study, Dr. Mark N. Feinglos and Susan E. Totten from Duke University Medical Center in Durham, North Carolina, suggest that “the critical issue” in the development of diabetes may be total caloric intake and subsequent weight gain rather than the composition of the diet.

“We have to assume that calories trump everything else,” they write. “Our number 1 goal for the reduction of new cases of type 2 diabetes should be to reduce the intake of high-energy, low-benefit foods, particularly in young members of the most vulnerable populations.”

SOURCE: Archives of Internal Medicine, July 28, 2008.