Beyond the Mediterranean Diet: The Role of Omega-3 Fatty Acids in the Prevention of Coronary Heart Disease

Charles R. Harper, MD, Terry A. Jacobson, MD

Disclosures

Prev Cardiol. 2003;6(3) 

In This Article

Structure

Fatty acids consist of a hydrocarbon chain with a hydrophobic methyl group at one end and a hydrophilic carboxyl group at the other (Figure 1).[2] The methyl end of the molecule is also referred to as the omega end while the carboxyl group is located at the delta end. Fatty acids are described using the omega numbering system. In this system carbon atoms are numbered in order starting from the methyl end. The length of the carbon chain along with the location and number of the double bonds determines the properties of the different fatty acids. A fatty acid can be saturated (no double bonds), monounsaturated (one double bond), or polyunsaturated (two or more double bonds).[3]

Important fatty acids. The number of carbon atoms is indicated before, and the number of double bonds is indicated after, the colon. The position of the first double bond counted from the methyl end is listed after the comma.

PUFAs may be divided into two subcategories, the n-3 and the n-6 fatty acids. The n-3 PUFAs have their first double bond located at the third carbon molecule (C-3) while the n-6 PUFAs have their first double bond located at (C-6). The n-6 and n-3 PUFAs are considered "essential" fatty acids because humans cannot synthesize them and they must be included in the diet. The n-3 fatty acid, ALA, and the n-6 fatty acid, linoleic acid (LA), are the predominant essential fatty acids in humans.[3] LA can be elongated and desaturated to arachidonic acid while ALA is elongated and desaturated into EPA and then into DHA (Figure 2). EPA and DHA are the major n-3 fatty acids found in fish and are thought to be responsible for their cardioprotective effect.[4] It is thought that ALA conversion to EPA is dependent on levels of the n-6 fatty acid LA because ALA and the n-6 fatty acids are competitive substrates for the rate-limiting enzyme 6 desaturase (Figure 2).[5] Leukotrienes, prostaglandins, and thromboxanes are eicosanoids that are derived from the above mentioned essential fatty acids. Eicosanoids derived from arachidonic acid are generally proinflammatory and proaggregatory agonists, while those derived from the n-3 fatty acids tend to inhibit platelet aggregation and be anti-inflammatory or cause less inflammation.[6] EPA and DHA are found predominately in selected fish while ALA is found in flaxseed grain, canola (rapeseed) oil, certain nuts, and certain vegetables.

The pathways for the desaturation and elongation of omega-3 and omega-6 polyunsaturated fatty acid and eicosanoid production.

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