Featured article in the Summer 2015 Issue of Nutrition Close-Up; written by Beth H. Rice Bradley, PhD
The World Health Organization lists coronary heart disease (CHD) as the leading cause of death, globally. It is no surprise that policymakers, academicians, health professionals and health-conscious consumers are interested in ways to decrease the burden of CHD on society. For years, attention has been focused on decreasing saturated fat intake as a means to decrease the incidence of CHD. Recently, however, the tide has turned. The purpose of this article is to summarize the current knowledge on the link between saturated fat and CHD and to correct misperceptions that surround the topic.
CHD is the narrowing and hardening of the coronary arteries that supply oxygen-rich blood to the heart.1 It is a multifaceted disease caused by damage to the endothelial lining of the coronary arteries. When the endothelial lining is compromised as a result of smoking, high blood pressure, diabetes, oxidized small dense low-density lipoprotein cholesterol (LDL-C), or other factors, the inflammatory cascade that repairs the lining of the vessel can eventually become a site of plaque build-up and ultimately plaque rupture; causing heart attack.2
Saturated fatty acids contain no double bonds between the carbon atoms of the fatty acid chain, which means that carbon atoms are saturated with hydrogen. Sources of saturated fat include foods of animal origin, such as poultry, beef, lamb, pork, lard, and dairy products made from whole or 2% milk, as well as some plant-based oils, such as palm and coconut oil. Because baked and fried foods are made with fats and oils, these foods can also contain saturated fat.
Elevated LDL-C in the blood is associated with increased risk of CHD.2 Consuming saturated fatty acids tends to increase LDL-C levels in the blood. It is not surprising that for many years it was hypothesized that because saturated fats raised LDL-C, and because LDL-C was associated with CHD, that consuming saturated fatty acids caused heart disease. This hypothesis, however, is far too simplistic. Observational and clinical trials have since enhanced what we know about saturated fat consumption and risk of CHD. Fatty acids come in different chain lengths, and this makes a difference in how they are metabolized. For instance, stearic acid, C18:0, the most abundant fatty acid in milk, tends not to raise LDL-C to the extent that other saturated fatty acids do.3 Also, not all food sources of saturated fat are equal. Whole-milk dairy foods such as cheese and yogurt have been associated with a decreased risk of CHD in observational studies.4 Further, not all LDL-C is created equal. LDL-C comes in different sizes, with oxidizable small-dense LDL potentially being more atherogenic than large buoyant LDL. If these factors were not enough to poke holes in the saturated fat LDL-C CHD hypothesis, a recent and highly publicized meta-analysis of observational and clinical studies indicated that saturated fat consumption was not associated with elevated risk of CHD.5
Word has gotten out that saturated fats, in the collective sense, are not to blame for the leading cause of death among men and women in America. Time magazine recently published a cover story featuring a picture of butter under the headline Eat butter. Scientists labeled fat the enemy. Why they were wrong. Whereas Time got the message that the science around saturated fats and heart disease has evolved, the message that we eat foods (a diet), and not nutrients, was lost in the article. Whereas cheese and yogurt have been associated with a reduced risk of heart disease, the implication to eat butter is not based on any study that this author is aware of. Herein lies the issue of looking at the effect on CHD of a macronutrient, such as fat, and projecting it to the effect from food.
The PREDIMED study, designed to test the effect of a total diet on CHD, showed that among persons at risk for CHD, a Mediterranean Diet with extra-virgin olive oil or nuts reduced the incidence of major cardiovascular events compared to a control diet in which participants were advised only to reduce fat.6 The Mediterranean Diet used in PREDIMED contained saturated fat. It is an excellent example of a diet and disease trial that emphasized that saturated fat alone cannot be considered the culprit in the burden of heart disease.