Omega-3s – a general guide to their biochemistry and history

What ordinary folk consider to be fats are very different to what I shall be talking about here.  A fatty acid is essentially a string of beads, made of carbon, with two hydrogen atoms per carbon and single chemical links or "bonds" between each carbon. If all the links are single bonds the fatty acid is called a “saturated” fat. If one or more or the bonds is a double bond (with only one hydrogen attached to the carbons on each side of the double bond) it is called an "unsaturated fatty acid"

Oleic acid, the main fatty acid in olive oil, has a single double bond and so it is called a "monounsaturated" fatty acid.



Notice that there are eighteen carbons (the grey balls) with a single double bond in the middle.  The red balls are single oxygen molecules and the blue balls are hydrogens.  One of the oxygens has a hydrogen attached, so the right side terminal cluster is written as -COOH.  This is makes it acid, hence the term "fatty acid".  The grey ball at the opposite end to the acid grouping is called the "omega" or "n" carbon.

So what then is an omega-3 or omega-6 fatty acid?  Well, here's the chemical structure of EPA (eicosapentaenoic acid):


You'll notice that there are 5 double bonds, so it is a "polyunsaturated" fatty acid, or PUFA.  You'll also notice that the first double bond is on the third carbon from the left side (the omega end) so it is an "omega-3" fatty acid.  So let's look at another very important omega-3 fatty acid -- DHA (dosocahexaenoic acid): 


Here you'll notice that, once again, the first double bond is on the third carbon from the omega end but the carbon chain is longer, with 22 carbons to EPA's 20 and six double bonds rather than five.  In actuality, the presence of the double bonds bend and contract the structure so it looks more like this:



Here the carbons are still grey and the oxygens red, but the hydrogens are shown as white.

The point I'm making is that fatty acids, such as EPA and DHA, are unique chemical entities.  Since our body is unable to manufacture enough of these for our needs from alternative dietary and internal souces, and they are vital to our normal health, these are called "essential fatty acids".  This implies that the only reliable source of them in the normal diet is from fish and other marine foods, such as shellfish.

The vitally important question then is just how important are these unique dietary ingredients to human health, and in particular to the health of our brains and minds? 


If one of the links is a double strand (a double bond), it is called a “monounsaturated” fat, a good example of which is oleic acid. Olive oil, with its large amounts of oleic acid, is an integral part of the so-called “Mediterranean diet”, which reduces blood cholesterol and lessens the risk of suffering a heart attack. If two or more of the links in a fatty acid are double-stranded, it is called a polyunsaturated fat, also called a polyunsaturated fatty acid, or PUFA. All of the fatty acids that are essential to human health are polyunsaturated fatty acids, or PUFAs. 

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