Replacing fat in the diet with vegetables, fruits, and whole grains does not lead to increased body weight in postmenopausal women, according to results of the Women’s Health Initiative Dietary Modification Trial.

Some proponents of popular diets have low-fat and high-carb diets for the increased prevalence of obesity in the US over the past several decades, Dr. Barbara V. Howard and her associates note in their report, published in this week’s Journal of the American Medical Association.

To assess this premise, Howard, from MedStar Research institute in Washington, DC, and her colleagues evaluated long-term weight changes among nearly 49,000 women ages 50 to 79 enrolled between 1993 and 1998 in the WHI trial.

Abut a third of the women were randomly assigned to participate in group and individual sessions that promoted a reduction in total dietary fat to 20%, at least five servings daily of fruits and vegetables, and six servings of grains, but no restriction in calories. The other women received diet- and health-related educational materials only.

During the first year, mean weight decreased significantly in the intervention group by 2.2 kg (p < 0.001), but not in the control group. Although average weight in the intervention group tended to increase over time, it remained below baseline and significantly lower by 0.5 kg than the comparison group for nine years.

“A low-fat dietary pattern may help attenuate the tendency for weight gain commonly observed in postmenopausal women,” Howard’s team concludes.

However, editorialists from Tufts University, Dr. Michael L. Dansinger and Dr. Ernst J. Schaefer, call the study’s findings on long-term weight change “underwhelming,” and suggest that the intervention should have also included advice on caloric restriction for participants who were overweight or obese.

They reported in 2005 that cutting calories resulted in weight loss and heart disease risk factor reduction, regardless of diet type.

“Much more work needs to be done on the obesity front,” the Boston-based writers advise, “including a concerted collective effort focused on developing reliable methods of facilitating high long-term adherence levels to substantial lifestyle efforts - specifically calorie-reduced eating patterns and much more exercise.”

SOURCE: Journal of the American Medical Association, January 4, 2006.