Clinical Question: Do low-fat, high-carbohydrate diets increase the risk of obesity among postmenopausal women?
Setting: Outpatient (any)
Study Design: Randomized controlled trial (single-blinded)
Synopsis: Controversy exists about whether diets with a lower proportion of fats increase the risk of obesity. The investigators randomly assigned (uncertain allocation concealment) 48,835 postmenopausal women between 50 and 79 years of age to a low-fat dietary intervention (n = 19,541) or a self-select dietary control group (n = 29,294). Women in the intervention group attended a series of sessions designed to promote a decrease in total dietary fat (to 20 percent) and an increase in the consumption of fruits, vegetables, and whole grains. Participants were informed that the diet was not intended to promote weight loss. Women in the control group received general dietary educational information and were allowed to select their diet. Patients self-monitored their diet using a food-frequency questionnaire.
The completion rate for the questionnaire was 81 percent at eight years. Individuals blinded to treatment group assignment performed anthropometric assessments. Using intention-to-treat analysis, women in the intervention group lost weight in the first year (mean = 4.9 lb [2.2 kg]) and maintained significantly lower weights than women in the control group (difference of 4.2 lb [1.9 kg] at one year and 0.9 lb [0.4 kg] at 7.5 years). There was no evidence of weight gain over baseline values among women in the intervention group at any time during follow-up. In addition, no trend toward weight gain was observed in any stratification of age, ethnicity, or body mass index.
Bottom Line: Following long-term recommendations to reduce dietary fat and increase consumption of fruits, vegetables, and whole grains does not cause weight gain among post-menopausal women. (Level of Evidence: 2b)