Principles of Biochemistry

6.3.2.5 Omega-3 and Omega-6 Fatty acids

6.3.2.5 Omega-3 (ω3) and omega-6 (ω6) fatty acids

Omega-3 (ω3) and omega-6 (ω6) fatty acids are unsaturated “Essential Fatty Acids” (EFAs) that need to be included in the diet because the human metabolism cannot synthesis them from other fatty acids.

Since these fatty acids are polyunsaturated, the terms n-3 PUFAs and n-6 PUFAs are applied to omega-3 and omega-6 fatty acids, respectively. These fatty acids use the Greek alphabet (α,β,γ,...,ω) to identify the location of the double bonds.The “alpha” carbon is the carbon closest to the carboxyl group (carbon number 2), and the “omega” is the last carbon of the chain because omega is the last letter of the Greek alphabet.

Linoleic acid is an omega-6 fatty acid because it has a double bond six carbons away from the “omega” carbon. Alpha-linolenic acid is an omega-3 fatty acid because it has a double bond three carbons away from the “omega” carbon

 

Linoleic acid plays an important role in lowering cholesterol levels.

Arachidonic acid is an omega-6 fatty acid. This type of terminology is sometimes applied to oleic acid which is an omega-9 fatty acid. In these simplified structural formulas all the double bonds have the Cis configuration.

These two, linoleic acid (LA) and alpha linolenic acid (ALA), are widely distributed in plant oils.

In addition, fish oils contain the longer-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Other marine oils, such as those from whale, seal, porpoise etc. also contain significant amounts of docosapentaenoic acid (DPA), which is also an omega-3 fatty acid.

Although the body, to some extent, can convert ALA into these longer-chain omega-3 fatty acids, the omega-3 fatty acids found in marine oils help fulfill the requirement of essential fatty acids.