Low-Fat Dietary Pattern and Risk of Cardiovascular Disease: The Women???s Health Initiative Randomized Controlled Dietary Modification Trial

Abstract

There is not yet sufficient information to determine whether a diet that is low in fat and high in fruits, vegetables, and grains can lower the risk of cardiovascular disease (CVD). This hypothesis was tested in the Women's Health Initiative Dietary Modification Trial, a randomized, controlled study enrolling 48,835 postmenopausal women ranging in age from 50 to 79 years. The major dietary goal was to lower the intake of total fat to 20% of energy intake by eating 5 or more servings per day of fruits and vegetables and at least 6 servings of grains. Women assigned to the intervention were asked to attend 18 group sessions in the first year and then quarterly sessions conducted by specially trained, certified nutritionists. The group activities were supplemented by individual interviews. Forty percent of women were assigned to the intervention, whereas 60% in a comparison group were given written dietary guidelines and other health-related materials. The participants, seen at 40 U.S. clinical centers in the years 1993-1998 were followed up for 8.1 years on average. The demographic characteristics of this ethnically diverse study population were comparable in the intervention and comparison groups. After 6 years, the intervention group had an 8.2% lower mean total fat intake and a 2.9% lower mean saturated fat intake than at baseline. They ate less trans, monounsaturated, and polyunsaturated fat and cholesterol, but the ratio of polyunsaturated to saturated fat did not change. The dietary intervention was associated with small but significant reductions in body weight, waist circumference, and diastolic blood pressure. Serum levels of low-density lipoprotein cholesterol declined, but there were no significant changes in high-density lipoprotein cholesterol, triglycerides, or lipoprotein(a). The dietary intervention was not associated with significant changes in major coronary heart disease (CHD), which included myocardial infarction and death from CHD; composite CHD (CHD/coronary revascularization); or total, fatal, or nonfatal strokes. After excluding women with a history of CVD at baseline, the hazard ratio for CHD was 0.94 (95% confidence interval, 0.86-1.02), and that for stroke was 1.02 (95% confidence interval, 0.90-1.17). There was a trend toward greater reductions in CHD risk in participants with lower intakes of saturated fat or trans fat, and in those eating more vegetables and fruits. Hazard ratios did not change after considering adherence criteria based on participation in the interventional activities. The low-fat diet given to postmenopausal women in this study for approximately 8 years on average failed to appreciably reduce the risk of CHD or stroke. It may be that a more focused diet with greater changes in multiple macro-and micronutrients, along with alterations in behaviors that influence CVD risk factors, will be needed to achieve a substantial impact on manifestations of CVD.