I brought you a tuna sandwich. They say it’s brain food. I guess because there’s so much dolphin in it, and you know how smart they are. Marge Simpson

As will be seen from the list below, a number of omega-3 fatty acids exist in nature. 

Dietary Omega-3 (n-3) Fatty Acids

alpha-linolenic acid (ALA) - 18:3; docosahexaenoic acid (DHA) - 22:6; eicospentaenoic acid (EPA) - 20:5; stearidonic acid - 18:4;
eicosatetraenoic acid - 20:4; docosapentaenoic acid - 22:5


The numbering is a chemical convention which tells you that, say, alpha-linolenic acid has 18 carbons with three chemical double bonds.  Traditionally the formula would include (n-3) after the 18:3, written 18:3 (n-3) to add that the first chemical double bond is on the third carbon from the omega end of the chain.

Only three of these, ALA, EPA and DHA are regarded as essential to human health.  Formerly, nutritionists and biochemists regarded ALA as the key essential fatty acid since the other two can be manufactured from it in the body.  But we now recognise that the manufacturing ability is exceedingly limited (even more so at the extremes of foetal immaturity and old age) so we now regard all three as "essential" to normal health.

Dietary Omega-6 (n-6) Fatty Acids


It is also vitally important to grasp that there are very important interactions between the omega-3s and the omega-6s in the human body.  The complexity is beyond this article but professional visitors may be interested to visit the wikepedia website, and this page in particular:
 
 http://en.wikipedia.org/wiki/Essential_fatty_acid_interactions

The modern "Western" diet contains much less omega-3 fatty acids than the diet of a century ago - and the diet from a century ago had much less omega-3 than the diet of our hunter gatherer ancestors, who lived in coastal regions, or by the banks of rivers and lakes and who consumed relatively large amounts of fish and shellfish.  

If we look at the ratio of omega-3 to omega-6 in in our diet and compare it to our ancestors, we find that we consume a far higher proportion of omega-6 to omega-3 than they did.  This has been accompanied by increased rates of many diseases – the so-called diseases of civilisation, which includes heart attacks, age related cognitive decline and dementia, as well as diseases in which internal inflammation afflicts the body's organs and tissues - for example rheumatoid arthritis and dle.

A new study reported in New Scientist (28 June 2008, page 18) confirms that increasing the intake of omega-3s improves intelligence, particularly so in girls, while increasing consumption of omega-6s decreases intelligence.  

As we have seen, there is also evidence, albeit more preliminary, that this high omega-6 to omega-3 ratio may make us more liable to several psychiatric disorders.

The two key questions then are:

1.  What is the desirable ratio of omega-3 to omega-6 in our diet?

2.  How do we achieve this in the hubble, bubble, toil and struggle of everyday living?

I have taken the benchmark established by authors such as Yehuda and his colleagues in recommending a ratio of 1: 4 omega-3 to omega-6.  But while it is easy enough to appreciate the scientific theory behind this, in practice it is difficult to show ordinary families how to achieve this in the day-to-day struggle of calculating diets, shopping at supermarkets and right down to the ingredients and practicalities of cooking.



This is a scale drawing of the ideal ratio of omega-3s to omega-6s.  Note that the omega-3 arm is longer than the omega-6, to represent that the internal chemistry has a preference for omega-3s that allows this level of omega-6 surplus to operate efficiently and healthily in normal circumstances.

Unfortunately, the typical Western diet contains a ratio of omega-3 to omega-6 of less than 1: 10 - and sometimes much less.  


This is a scale drawing of the actual ratio as consumed by people in the UK and America.

For example cottonseed oil, peanut oil, grapeseed oil and corn oils contain little or no omega-3.  Even olive, peanut and canola oils consist of approximately 80% monounsaturated fatty acids, (i.e. neither omega-6 nor omega-3) so they contain relatively small amounts of omega (3 & 6) fatty acids. 

The only normal dietary source of DHA and EPA come from fish and marine foods, such as shellfish.  Since I advocate less than a gram of these combined per day, whether through eating fish and shellfish or, for those who will not or cannot eat fish and shellfish, through taking a fish oil or omega-3 supplement, most of the omega-3 in the diet must come from alpha-linolenic acid, the vegetable derived omega-3.  But even here I do not recommend that people go to extremes.  8 grams of omega-3 in total per day would be sufficient. 
Foods that contain high levels of vegetable type omega-3 include rapeseed oil as well as the oils of soybeans, walnuts flaxseed, perilla, chia and hemp.  Some of these find their way into vegetable cooking oils and margarines, but you won't usually be able to tell from the packaging, which tends to lump all the polyunsatures into a single figure.  But you can guarantee a good intake from the green leaves of broadleaf plants, whose membranes are responsible for photosynthesis, as well as from the products of animals that feed on greens. 

So now you know why I put such emphasis into greens in my recipes and fourteen-day planner!  

Realising that it was difficult for busy people to work out the right dietary balances, I devoted the second half of The Brain Food Diet to explaining the fat balances, the best fish to eat, actual recipes not only for including oily fish in the diet but also other recipes aimed at reducing saturated fat and thus reducing the risk of vascular dementia.  I even spent time working out a two week day-to-day menu planner to give advice and a basic layout to people who might otherwise find themselves struggling to work the science into practical buying, cooking and eating.

Further reading

Why not visit the Wikipedia free advice page on omega-3:
http://en.wikipedia.org/wiki/Omega-3_fatty_acid#_note-NIHefaeducationpage

Berr C (2000). Cognitive impairment and oxidative stress in the elderly: results of epidemiological studies. Biofactors 13: 205-09.

Deschamps V, Barberger-Gateau P, et al (2001). Nutritional factors in cerebral aging and dementia: epidemiological arguments for a role of oxidative stress. Neuroepidemiology 20: 7-15.

Dye, L and Lluch A (2000). Macronutrients and mental performance. Nutrition 16: 1021-34.

Gonzalez-Gross M, Marcos A, et al (2001). Nutrition and cognitive impairment in the elderly. Br J Nutr 86: 313-21.

Hepburn FN, Exler J, and Weihrauch JL (1986). Provisional tables on the content of omega-3 fatty acids and other fat components of selected foods. J Am Diet Assoc 86: 788-93.

Jama JW, Launer LJ, et al (1996). Dietary antioxidants and cognitive function in a population-based sample of older persons. Am J Epidemiol 144: 275-80.

Masaki KH, Losonczy KG, et al (2000). Association of vitamin E and C supplement use with cognitive function and dementia in elderly men. Neurology 54: 1265-72.

Sies H and Stahl W (2004). Carotenoids and UV protection. Photochem Photobiol Sci 3: 749-52.

Sies H and Stahl W (2004). Nutritional protection against skin damage from sunlight. Ann Rev Nutr 24: 173-200.

Solfrizzi V, Panza F, et al (1999). High monounsaturated fatty acids intake protects against age-related cognitive decline. Neurology 52:1563-69.

Yehuda S, Rabinovitz S, et al (2002). The role of polyunsaturated fatty acids in restoring the aging neuronal membrane. Neurobiol. Aging 23: 843-853.

Yehuda S (2003). Omega-6/Omega-3 Ratio and Brain-Related Functions. In Simopoulos AP, Cleland LG (eds). World Rev Nutr Diet, Karger 92: 37-56.

Yehuda S, Rabinovitz S and Mostofsky DI (2005). Essential fatty acids and the brain: from infancy to aging. Neurobiol.Aging 26(S): S98-102.  

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