The prevalence of obesity in the US has dramatically increased over the past four decades. There is no shortage of popular weight loss diets, but there is some controversy as to which diets are most effective. A number of popular diet books contend that the low-fat, high-carbohydrate diets recommended by organizations such as the American Heart Association and the American Cancer Society have contributed to the increase in obesity.

A new study in the January 4, 2006 issue of the Journal of the American Medical Association examined the relationship between weight changes and diet in postmenopausal women. The researchers found that a low-fat diet high in vegetables, fruits, and grains did not result in weight gain.

About the Study

This study included 48,835 postmenopausal women ages 50-79 participating in the Women’s Health Initiative (WHI) Dietary Modification trial. Forty percent of the participants were assigned to an intervention diet consisting of 20% fat, five or more servings of vegetables and fruit per day, and six or more servings of grains per day (whole grains were encouraged). The women were encouraged to maintain their usual calorie intake. The other participants were assigned to a control group, and received diet and health-related educational materials. The researchers followed the participants for an average of 7.5 years, used food frequency questionnaires to monitor dietary intake, and measured their weight annually.

The women in the intervention group lost an average of 4.8 pounds after one year, while those in the control group did not lose any weight. While the weight loss diminished over time, the intervention group maintained a significant 1.1-pound greater weight loss than the control group after nine years. Overall, the women who reduced their fat intake the most lost the most weight, and those who increased their fat intake by 3% or more gained weight. Greater weight loss was associated with greater increases in vegetables, fruits, fiber, and carbohydrates.

This study is limited because it only included postmenopausal women ages 50-79, so its results may not apply to other populations. In addition, the food frequency questionnaire required the participants to recall food intake throughout a three-month period, which could result in error.

How Does This Affect You?

This study adds to previous research that suggests that a low-fat diet rich in fruits, vegetables, and grains is not associated with weight gain. In fact, it may actually help prevent weight gain in postmenopausal women. This study was not designed to promote weight loss, and if the women in the study had reduced their calorie intake, they would have likely experienced more substantial weight loss.

But, the biggest challenge we face in the battle against the bulge today seems to be dietary adherence—not finding the optimum diet prescription. Evidence shows that, when strictly adhered to, different diet types (i.e., Atkins, Zone, Weight Watchers, and Ornish) all result in successful weight loss. But no diet has yet shown consistent success over the long term. Since the key is perseverance over the long haul, don’t waste your time with a diet you are unprepared to commit to for the rest of your life.