Omega-6 Vegetable Oils and Heart Disease
American Heart Association OKs Linoleic Acid and Arachidonic Acid
Feb 6, 2009
The modern shift to polyunsaturated fatty acids (PUFAs) was accompanied by the rise of inflammatory/degenerative diseases as the major medical killers in the Western world. Treatments for degenerative diseases associated with aging have improved, but these diseases have become more prevalent and the age of onset has decreased. And medical costs have skyrocketed. Omega-6 vegetable oils seem to be the problem, but the American Heart Association (AHA) has given these PUFAs a clean bill of health (reference below).
Experimental Basis for AHA Support for Omega-6 PUFAs
- Short PUFAs found in the diet, e.g. linoleic acid (LA), are inefficiently (1-10%) converted to the long PUFAs that serve as the precursors of cellular hormones.
- Omega-6 arachidonic acid (AA) is the starting point for the conversion to most of the inflammatory and anti-inflammatory cellular hormones, e.g. prostaglandins, leukotrienes and lipoxins.
- Increases in blood plasma AA are associated with anti-inflammation, not inflammation.
- Increases in dietary AA and/or LA result in a decrease in cardiovascular disease. Replacing dietary saturated fat with PUFA leads to a reduction of disease by 25-50%. Higher serum LA translates into less disease.
- Increases in dietary LA result in lower serum cholesterol and LDL, but paradoxically they also lead to a narrowing of arteries.
Inflammation is the Cellular and Tissue Response to Many Stresses
It is difficult to identify the sources of inflammation in experimental studies. In cardiovascular disease, the causes of inflammation leading to the disease symptoms are commonly not known in individual cases and the cardiac symptoms are treated. There are actually many different diseases, all with different sources of inflammation, pigeon-holed under the same symptom, a cardiac event. The most effective long term treatment for the diverse group is general suppression of inflammation. Any specific treatment of a root cause only works on a small subset of the group and would be considered ineffective. Statins, for example, are effective in reducing cardiovascular disease, because they reduce inflammation. The JUPITER study suggested that lowering LDL was of less importance in controlling cardiovascular disease.
Omega-6 Vs. Omega-3
Omega-6 and omega-3 fatty acids are not in opposition. Both types of PUFAs are needed for cells to respond to stress with inflammation and then return to normal. It is a cycle, not two opposite processes.
Omega-6 PUFAs are needed for both inflammation and restoration of normal cellular functions. Some of the enzymes produced during inflammation are needed to produce anti-inflammatory hormones from AA for cells to return to normal. The difficulty comes when inflammation is sustained, components, e.g. EPA, are depleted and the cycle cannot be completed. The result then is chronic inflammation, the symptoms of metabolic syndrome and degenerative diseases.
Why Have Omega-6 Vegetable Oils Been Condemned?
It seems wise not to trust medicine, dietitians and the food industry, because they have changed course so many times and made so many lamentable dietary suggestions. Professional societies like the AHA also frequently give advice that is even questioned by their members, because the advice doesn’t reflect the best information from the biomedical literature. So it makes sense to be skeptical.
In addition to reasonable skepticism, several major studies have concluded that omega-6 fatty acids, prominently found in common vegetable oils, increase the risk of cardiovascular disease.
The AHA Was Half Right
With its omega-6 promotion, the AHA appears to be at least partially right. Under many circumstances, an overabundance of omega-6 fatty acids permits a progression from inflammation and back to normal cellular and tissue physiology. However, an overabundance of omega-6 fatty acids with inadequate EPA and DHA may lead to problems. The result would be inadequate EPA conversion to anti-inflammatory prostaglandins and failure to return to normalcy. This would be a particular weakness in the presence of a large depletion of the EPA pools during sustained inflammation and chronic inflammation would result.
Thus, the AHA promotion of omega-6 PUFAs is half right. They should have said that omega-6 fatty acids are not a problem, if there is adequate EPA/DHA and no sustained inflammation. Unfortunately, the Western diet provides inadequate EPA/DHA and deficiencies that constantly produce inflammation. Of course, those enjoying an anti-inflammatory diet and lifestyle have biochemical tolerance for the AHA’s suggestions. Others eat vegetable oils at their peril.
Reference:
Harris WS, Mozaffarian D, Rimm E, Kris-Etherton P, Rudel LL, Appel LJ, Engler MM, Engler MB, Sacks F. 2009. Omega-6 Fatty Acids and Risk for Cardiovascular Disease. "A Science Advisory From the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention." Circulation. 2009 Jan 26. [Epub ahead of print]
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