The long-awaited results of the Women's Health Initiative Dietary Modification Trial are finally in. In this comprehensive research, 49,000 women aged 50 to 79 were followed for eight years. This is probably the first time that a study this large and this long has attempted to change eating behavior and track the results, so the medical community has been pretty excited. This is why it has been called “The Rolls Royce of Studies.”
The women in the study had to go to educational and support groups to help them make the change. After 8 years of following the diet as best they could (although they drifted upwards in fat consumption during the study, they continued to eat less fat than those in the comparison group), the women on the low-fat diet had essentially the same amount of breast cancer, colon cancer, heart disease, and stroke as the comparison group.
The women also were instructed to increase their consumption of fruits, vegetables, and grains. They ate on average only one more serving of fruits and veggies than the control group (4.9 servings compared to 3.8) and about half a serving of grain more (however, both groups were actually eating less grain by the end of the study). It is possible that if they ate more fruits and vegetables, which has been shown to be beneficial in other studies, their diet would have been more protective, but that might also have muddied the waters in looking at the effects of cutting fat.
Critics of the study, including low-fat guru Dean Ornish, insist that the reason no results were obtained was that the women were still eating too much fat (29% by the end of the study), and that the study was not long enough. But science writer Gina Kolata in her New York Times article, interviewed impartial statistician David Freedman who stated that the studies were well-designed and the results should be taken seriously. He also said, “We, in the scientific community, often give strong advice based on flimsy evidence. “
Update 2/15/06: My Opinion on the Media Response to This Study
Regina Wilshire, who writes a low-carb science blog, has an interesting commentary: Low-Fat Diets at the Crossroads
More Details about the Women's Health Initiative Dietary Modification Trial
- 48,835 women were enrolled, most between the ages of 50 to 69, with the mean age being 62.3 in both groups.
- 40% were in the intervention group, which received education and support with a goal of eating 20% of their diet from fat and 5 servings of vegetables and fruits per day.
- The groups were matched on the following characteristics: age, race/ethnicity, education, income, body mass index, family history of “premature” heart disease, hormone therapy, smoking history, blood pressure, cholesterol history, treatment for diabetes, history of cardiovascular disease alcohol use, colonoscopy history, history of polyps in colon, and aspirin use. Additionally, they were “retrospectively screened” for metabolic syndrome, which affected 36% in both groups.
- The following were tracked: weight, BMI, waist circumference, physical activity, blood pressure, cholesterol, triglycerides, blood glucose, blood insulin, insulin resistance, and a few other things. While there were a few statistically significant differences, they were so small that they seem unimportant, such as the low-fat group had a waist circumference that was slightly less than one centimeter less than the comparison group.
- The low-fat group ended up eating more carbohydrate (54% of calories) than the comparison group (46%) This is less than is usually advised.
- The low-fat group ate slightly more fiber (2.5 grams) but neither ate the recommended levels.
- Source of fat (saturated, trans, etc) was not specified; however the low-fat group ate less of all kinds of fat.
- The low-fat group exercised a bit more then the comparison group.
- The low-fat group ended up about 1.5 lbs lighter, on average, than the comparison group.
