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Holy mackerel? We're eating far too little fish these days 

Have you noticed how much publicity "omega 3s" have been receiving lately? More and more manufacturers seem to be fortifying common foods with them and almost every day a new article appears about the benefits of consuming omega 3 supplements. Some seem to think them almost elixirs of life. Predictably this enthusiasm has been accompanied by a backlash from critics such as Ben Goldacre who argue that most of the publicity is just hype without significant evidence to back it up. Furthermore many of the enthusiasts are individuals who stand to gain enormously from sales stimulated by the hype. And some have turned out to be distinctly dodgy. Patrick Holford claimed that you could cure Aids with Vitamin C, a view endorsed by HIV denier Thabo Mbeki, former president of South Africa; sadly this misinformation may have contributed to thousands of unnecessary Aids deaths. Gillian McKeith, star of TV's You Are What You Eat, plugged chlorophyll tablets claiming that they would oxygenate your blood, forgetting that it would be broken down by the gut and even if it worked there, there is not much light in the gut for photosynthesis to produce oxygen. Both were disciplined by the Advertising Standards Authority. 

Still, the food supplement industry is worth nearly $30 billion per annum in the US. Much of it is based on miracle personal stories without the support of proper scientific studies such as randomised control trials. Nevertheless, among all the headline-grabbing stories that are easy to dismiss, there is probably a kernel of truth about the importance of omega 3s to our health; it would be a mistake to throw out altogether the baby of true effects with the bathwater of unsupported hype. Why do omega 3s deserve our attention?

In the 1920s George and Mildred Burr discovered that two long-chain unsaturated fatty acids, named alpha linolenic acid (ALA) and linoleic acid (LA), were essential in the diet because mammals cannot synthesise these molecules from simpler components. ALA and LA are found in seeds such as rape or flax; they consist of 18 carbon atoms in a long chain. They are called "unsaturated" because eight of the carbon atoms are joined by double bonds. ALA is called "omega 3" because the first of the four carbon double bonds is three carbons away from the methyl end of the molecule. LA is termed omega 6 because the first double bond is six carbons away from the methyl end. They are truly essential and you would die if you did not consume them.

However, these 18 carbon fatty acids are not the ones the body actually uses.  A crucial constituent of our nerve and muscle membranes is a 22-carbon chain, docosahexanoic acid (DHA) that has six double bonds, while a 20-carbon omega 3 acid, eicosapentanoic acid (EPA), is the basis of many vital anti-inflammatory signalling molecules called eicosanoids. Many animals are good at elongating the seed-derived 18-carbon chains into these longer chains; but humans do this very inefficiently. Oily fish concentrate EPA and DHA which they  gain from algae in the sea. Hence so long as we humans eat oily fish regularly, as we used to, we obtain most of the EPA and DHA that we need to keep body and brain healthy.

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