TUESDAY, Jan. 3, 2006 (HealthDay News) -- A diet low in fat and higher in fruits, vegetables and whole grains did not cause weight gain in postmenopausal women, new research found.
"Postmenopausal women are at an age where they get this little bump in weight," said Eva Obarzanek, a research nutritionist with the National Heart, Lung, and Blood Institute, which funded the study. "Following this diet isn't going to cause a weight gain."
The study is the largest randomized dietary intervention trial yet attempted and is part of the U.S. government-sponsored Women's Health Initiative (WHI).
It's not yet clear, however, if this is the best overall diet for women in this age group.
A growing number of people in the United States and around the world are becoming overweight or even obese. In searching for explanations, experts have focused on diet and nutrition. Some blame low-fat, high-carbohydrate diets that are advocated by many health and government agencies.
According to background information in the study, most government and disease-specific organizations now recommend diets in which fats represent 20 percent to 35 percent of calories, and total carbohydrates -- those derived from fruits, vegetables and grains, for instance -- represent 45 percent to 65 percent of total calories.
"People have been questioning whether low-fat diets are good," Obarzanek explained. "Just as the percentage of fat in diets has been decreasing since the late 1970s, at the same time the prevalence of obesity has gone up. Is there a connection?"
This trial, the WHI Dietary Modification Trial, was designed to look at the effects of a low-fat diet, high in vegetables, fruits and grains, on breast and colorectal cancers and cardiovascular disease in postmenopausal women. Those results are not in yet, so the current paper looks only at weight gain.
The findings appear in the Jan. 4 issue of the Journal of the American Medical Association.
For the trial, 48,835 postmenopausal women in the United States were randomly assigned to a low-fat dietary intervention or to a control group and then were followed for a mean of 7.5 years.
Women in the low-fat dietary group attended both group and individual sessions on how to decrease fat intake and increase vegetable, fruit and grain consumption. There were no instructions or guidelines on weight loss or calorie restriction.
The control group received diet-related education materials.
Women in the low-fat dietary group lost a mean of 2.2 kilograms (4.8 pounds) in the first year. After that, they maintained a lower weight than the women in the control group and did not exceed their baseline weight at any time during the study.
Women who decreased the amount of calories they were consuming from fat lost the most weight. Weight loss, albeit not as great, was also seen in women who increased vegetable and fruit servings. Weight loss was also seen among women who increased their fiber consumption, but this was not considered significant, the researchers said.
"These results do not support previous notions that a low-fat diet is the cause of the obesity epidemic," Obarzanek said. "This pretty much shows that certain things we do now are healthful, such as low saturated fat intake."
The question of whether such a diet has a beneficial effect on other health matters is still an open one.
"We really need to see the results of the trial to see whether following this diet is good for cancer or cardiovascular disease," Obarzanek said. "Let's see what happens."
More information
The U.S. Department of Agriculture has more on low-fat diets.
