Dietary Fat: At the Heart of the Matter
The role of dietary fat in the causation of coronary heart disease (CHD) has
long been a topic of interest and dispute. In his News Focus article, Gary
Taubes discusses what he calls "The soft science of dietary fat" (30 Mar., p.
2536). He reviews the history of the diet-heart issue and concludes that public
health recommendations regarding dietary fat have not been based on solid
science. He is primarily critical of the "low-fat" recommendation that has long
been made by authoritative bodies to the American public. Taubes covers many
aspects of the diet-heart issue, but he focuses on the question of whether
there has been an overemphasis on fat without sufficient evidence that dietary
fat is a major cause of CHD. He points out that recent trends in heart disease
mortality both in the United States and worldwide are not well correlated with
changes in dietary fat intake. Certainly he makes several astute observations,
but in some areas, particularly in cardiovascular epidemiology, he does not
appropriately recognize several other factors that confound the role of certain
dietary fats in causation of CHD.
In my view, Taubes does not rightly identify saturated fatty acids as the
predominant dietary factor contributing to the development of CHD. The
significance of saturated fatty acids has been demonstrated by an enormous
number of high-quality studies carried out with dietary fat in the fields of
animal research, epidemiology, metabolism, and clinical trials (1). Although
all questions have not been answered, a clear picture of the metabolic and
health effects of saturated fatty acids has emerged. One fact is
incontrovertible. As shown in multiple metabolic studies in humans, saturated
fatty acids as a class, compared with unsaturated fatty acids and carbohydrate,
raise serum low-density lipoprotein (LDL). Evidence is abundant that elevated
LDL is a major cause of CHD and that lowering serum LDL levels reduces CHD risk
(2). Even moderate reductions in LDL levels, such as those obtained by reducing
dietary saturated fatty acids, are projected to substantially reduce risk of
CHD in populations (3). Early prospective epidemiological studies gave results
that are consistent with these projections (4). For example, in Northern and
Eastern Europe, where intake of animal fats (mostly saturated fatty acids)
previously was very high, serum LDL levels and CHD rates also were high.
Conversely, in Southern Europe, where plant oils (mostly unsaturated fatty
acids) are the predominant fat source, serum LDL levels and CHD rates were much
lower. These relations were established more than 30 years ago, before
increasing social and cultural homogenization in Europe partially obscured the
relation of dietary fat to CHD (4). These population results, which in
themselves were suggestive although perhaps not definitive, have been confirmed
by results of controlled clinical trials. Several trials reveal that
substitution of unsaturated fatty acids for saturated fatty acids lowers the
incidence of CHD (1).
Although Taubes acknowledges the difference between saturated and unsaturated
fatty acids, he does not draw a clear enough distinction in his discussion of
dietary fats in general. Consequently, the article obscures the potential for
public health benefits of substituting unsaturated for saturated fatty acids in
the American diet. Such confusion does a disservice to the public health effort
to further reduce the incidence of CHD through a reduction in intake of
saturated fatty acids. On the other hand, Taubes does rightly note that other
nutritional factors, for example energy imbalance leading to obesity, excessive
carbohydrates, and insufficient intake of fruits and vegetables also influence
population risk for CHD (1, 2).
Scott M. Grundy
Center for Human Nutrition and the Departments of Clinical Nutrition and
Internal Medicine,
University of Texas Southwestern Medical Center,
Dallas, TX 75390-9052, USA.
E-mail: scott.grundy @utsouthwestern.edu
References and Notes
1.
Report of the Dietary Guidelines Committee on the Dietary Guidelines for
Americans, 2000
(U.S. Department of Agriculture, Agricultural Research Service, Washington, DC,
2000).
2. Expert Panel on Detection, Evaluation, and Treatment of High Blood
Cholesterol in Adults,
J. Am. Med. Assoc.
285, 2486 (2001).
3. M. R. Law, N. J. Wald, T. Wu, A. Hackshaw, A. Bailey,
Br. Med. J.
308, 363 (1994).
4. A. Keys et al.,
Am. J. Epidemiol.
124, 903 (1986).
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