Fat and Heart Disease

For decades, the consumption of dietary fats, saturated fats in particular, has been associated with the risk of heart disease. Recently, however, this association has been strongly debated by many specialists.
Physiologically fats are long chains of carbohydrate molecules. The predominant fats in foods and in the body are triglycerides which are made up of three fatty acids attached to a glycerol molecule. Sterols, such as cholesterol and phospholipids, are also common types of dietary fat.

Fatty acids are chains of carbon and hydrogen, ending with a so-called carboxyl group. The chain lengths vary from 4 to 24 carbons. The term saturated implies that all hydrogen bonds are used (thus, the term saturated) and no more hydrogen atoms can therefore be incorporated into the molecule. The term unsaturated means that there is room for more hydrogen atoms, monounsaturated meaning that there is room for one such atom and polyunsaturated meaning that there is room for more than one atoms. Although so-called trans fats may be found in small amounts in nature, they are usually produced synthetically by partial hydrogenation of polyunsaturated fatty acids. This is done in food processing to make liquid oils more solid and to increase the shelf life of the product. Trans fatty acids have been shown to increase the risk of heart disease.

From a health perspective, there are certain fats that are considered important due to their proposed effect on heart disease. Polyunsaturated fatty acids, such as omega - 3 are considered healthy options. Usually, however, fats in food are a combination of saturated, monounsaturated and polyunsaturated fatty acids. We commonly tend to identify fat in the food based on the type of fatty acid that is predominant. Butter and steak for example predominantly contain saturated fatty acids and olive oil for example contains mainly unsaturated fatty acids.

The polyunsaturated omega - 6 and omega - 3 are building blocks for the so-called prostaglandins. The prostaglandins play an important role for inflammation in the human body. Omega-3 are building blocks for anti-inflammatory prostaglandins and the omega-6 are building block for inflammatory ones. Both these fats therefore play an important role. However, it has been suggested that the overabundance of omega-6 in the western diet compared to omega-3 may be undesirable.

Some studies indicate that consumption of saturated fats may increase blood levels of LDL-cholesterol (LDL-C). There is an association between blood levels of LDL- c and the risk of cardiovascular disease. Some studies have shown that replacing saturated fatty acids with polyunsaturated may decrease the risk of heart disease. Otherwise, there is indeed very weak scientific evidence linking saturated fat with increased risk for cardiovascular disease. For example, there is no evidence that that replacing saturated fats with carbohydrates is beneficial.

The main reason saturated fats are linked to an increased risk of heart disease is their tendency to elevate LDL-C. The lower the blood levels of this substance, the less risk of heart disease. This observation has been the main focus of dietary recommendations in heart disease prevention for decades. However, saturated fats seem to raise HDL-cholesterol (HDL-C) and lower triglycerides, which may actually reduce the risk of heart disease.

It is important not to confuse saturated fat with trans fat. Saturated fat is a natural fat found in animal products such as meat, milk and cheese. Saturated fat is also typically found in tropical oils such as coconut, palm and palm kernel oils. On the other hand, the majority of trans fats in our food are manufactured
Although saturated fats are often thought of as a group, it is important to keep in mind that they are not all the same. There are many different types of saturated fats and they may have different health effects. Grouping them all together is based on their chemical nature, not their effects on health. Saturated fats with carbon chain lengths of 14 (myristic) and 16 (palmitic), which are chiefly found in full fat dairy products and red meat, are most likely to increase blood levels of cholesterol. Stearic acid (18 carbon) which is also found in beef, and is the main fatty acid of cocoa butter, appears to increase cholesterol less.

A summary of available studies, recently published in The European Journal of Nutrition, indicated that dairy fat consumption does not increase the risk of heart disease. A metaanalysis, published 2010 in The American Journal of Clinical Nutrition, did not show an association between the intake of saturated fats and coronary artery disease.

Thus, the common assumption that saturated fats are associated with heart disease appears to lack scientific evidence.

Axel F Sigurdsson is an Icelandic cardiologist. He has a PhD degree from the University of Gothenburg, Sweden. He works at the Landspitali University Hospital in Reykjavik, Iceland and at the Heart Center just outside Reykjavik. He is a Fellow of The American College of Cardiology, The Swedish Society of Cardiolgy and The Icaelandic Cardiac Society.

He runs his own health blog, http://www.docsopinion.com, dedicated to health, nutrition, healthy lifestyle and prevention of disease.

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