Diets that are low in fat and high in carbohydrates from vegetables, fruits, and whole grains do not cause weight gain in postmenopausal women, reported Barbara V. Howard, Ph.D., and her associates in the Women's Health Initiative Dietary Modification Trial.
These results likely will hold true for younger women and for men of all ages, they said. So proponents of high-protein, high-fat, low-carb diets who blame the obesity epidemic on low-fat diets, are simply wrong, according to the WHI investigators.
“A number of popular diet books have suggested that increasing obesity may be attributed to the diets recommended for chronic disease prevention by various national health organizations,” the investigators wrote. Proponents of low-carb diets claim that the higher proportion of carbohydrates in these recommended diets actually promotes weight gain.
Dr. Howard and her associates found instead that a diet that replaces fat calories with calories from fruits, vegetables, and grains caused a modest weight loss. “Guidelines that restrict fat intake and advocate increases in complex carbohydrates have not been a contributing factor to the weight gain that has been occurring in the United States throughout the past several decades,” they noted (JAMA 2006;295:39–49).
The WHI dietary modification trial is a longitudinal study assessing the long-term effects of diet on breast and colorectal cancers and cardiovascular disease. Dr. Howard, of the MedStar Research Institute, Washington, and her associates used data from the trial to assess whether a low-fat diet caused weight gain.
The study followed 46,808 women of diverse ethnic and socioeconomic backgrounds, aged 50–79 years, for a mean of 7.5 years. Most of the subjects were overweight or obese, and all had a baseline fat intake that comprised at least 32% of their total daily calories.
A total of 27,994 subjects served as controls, adhering to their usual diets. In the intervention group, 18,814 women were encouraged to reduce their fat intake to no more than 20% of daily calories and to consume at least five servings of fruits and vegetables and at least six servings of grains daily.
The dietary intervention did not advocate caloric reduction and did not specifically aim to cause weight loss. Rather, the point was for the subjects to change to a healthier overall dietary pattern, the researchers said.
Nevertheless, mean weight decreased by 2.2 kg in the first year in the intervention group, and the women maintained a modest weight loss for the next several years. In contrast, weight did not change in the control group.
Women with the largest reduction in fat intake showed the greatest weight loss. Similarly, there was a statistical trend for greater weight loss in women who made the largest increases in the number of daily servings of fruits and vegetables, as well as in those who made the largest increases in fiber intake.