The Low‐Fat Diet That “Wasn't”

The subject of this column, of which all are aware, is the recent report from the Women's Health Initiative (WHI) that a “low”-fat diet does not reduce cardiovascular and other diseases.1 The study, which may be viewed as a problem of method rather than concept, confirms that “less is less” in regard to the benefits of a low-fat diet. Although the intent was to study a diet in which fat consumption comprised 20 percent of calories, actual fat intake during the study was 29 percent of calories, only a modest reduction from the average American diet (consumed by the control group) that is associated with the continuing epidemic of coronary heart disease. The impact of diet on LDL cholesterol is directly related to the reduction of calories supplied in the form of fat. The following relationships have been demonstrated for the influence of percent dietary fat and reduction of LDL cholesterol2: NCEP Step I diet (<30% total fat, <10% saturated fat), −9%; NCEP Step II diet (<30% total fat, <7% saturated fat), −15%; low fat diet (15% fat), −24%; very low fat (<10%), −35%. Reduction of saturated fat, the food element most related to heart disease, was not a component of the study, nor was a decrease in trans fats. That the participants did not lose weight indicates that any reduction in calories from decreased fat intake was likely replaced by sources such as carbohydrates. The detrimental effects of excess simple carbohydrates are well known. It is acknowledged that these issues were not as clear at the inception of the WHI as they are at present, but to meaningfully assess the effects of low fat consumption in a large, long-term trial, these factors must be addressed. The benefits of major restriction of saturated fat on blood lipids and coronary heart disease have been well documented in epidemiologic studies and smaller clinical trials. As it stands, the WHI studies may be viewed as “the low-fat diet that wasn't.” A more detailed analysis of the WHI studies will be presented in the Summer issue of Preventive Cardiology.