The McCarrison Society - Chairman's Comment Mar 2006

Chairman's Comment Mar 2006

This is a regular comments page by the Chair of the McCarrison Society, Dr Michael Crawford PhD CBiol, FIBiol, FRCPath.
Comment on Risks and benefits of omega 3 fats review, Lee Hooper et al BMJ, 24/03/2006
Meta-analysis of dietary interventions cannot be treated like drug trials.

All diagrams purporting to support the conclusion of Hooper et al (BMJ 24th March 2006) are based on relative risk - favours high or favours low omega 3 - which like a drug trial assumes the variable is only the omega 3 dose. This falsifies the review..

Efficacy of a fatty acid depends on which fatty acid(s), position in the glyceride, in the specific family or indeed the nature of a product (e.g phosphoglycerides, triglyceride, enteric) , dietary prehistory of individuals and importantly, on other fats in the diet which compete for receptors.

Moreover, it is DART II that skews the data. It was a stop start affair and used MAXEPA capsules. MAXEPA is an EPA rich oil derived from but not a fish oil!

The alternative was advice, which is notorious for non compliance. To put it bluntly, advice to eat fish if taken could be translated in different ways. Cardiff has good fish and chip shops or did they eat farmed salmon in butter and mayonnaise sauce and mashed potatoes cooked with margarine, to soak up the fats? Or did they eat raw salmon (Norwegian Gravidlax perhaps) , lightly grilled tuna or swordfish with a mixed salad and plain boiled potatoes or rice? Did they use olive oil or sunflower oil? These menus would have quite different effects. Careful validation with full reporting would be required to reach any degree of scientific acceptability.

In an attempt at validation DART II reports plasma levels of EPA in only 39 test compared to 29 control after 6 months fish advice = 4.58 (3.54) compared to no fish advice 3.03 (1.34) mg/dl. The standard deviation of the test is larger than the mean of the alleged control. Are these really different (no statistics are given)?.

Of critical importance, they do not report docosahexaenoic acid (DHA). Is that because there was no difference or maybe less? DHA is the principle cell membrane omega 3 fatty acid of the endothelium, smooth muscle cells, heart, immune, neural and other cells. The receptors are in the membrane and that is where you would want to see a difference if your measure was effective. There is relatively little EPA in the receptor sites. What is in the plasma can be very different to what is around the membrane receptors. Moreover control levels of EPA seem far higher than others report so maybe they are not measuring EPA at all. This is simply not a credible study and even its authors had concerns.

There is an abundant and robust science showing that other fatty acids in the diet (e.g saturated fats, linoleic, arachidonic acid) will affect differentially the utilisation of omega 3 fatty acids e.g. alpha- linolenic, stearodonic, eicosapentaenoic, docosapentaenoic or docosahexaenoic acids. Little attempt has been made by Hooper et al to control for these confounders. To illustrate the point, there is a recent review of long standing data (1) which concludes "that eicosapentaenoic acid and docosahexaenoic acid have differing haemodynamic and anti- atherogenic properties. The effects of the two fatty acids may also differ depending on the target population".

There is a lack of understanding in this review possibly because it is not the lead author’s field. However, that is no excuse. A meta- analysis which makes no attempt to control for these basic and varied metabolic and dietary confounding factors is simply valueless and likely to be misleading.

1. Mori TA, Woodman RJ. The independent effects of eicosapentaenoic acid and docosahexaenoic acid on cardiovascular risk factors in humans. Curr Opin Clin Nutr Metab Care. 2006 Mar;9(2):95-104

Competing interests: The health of the Nation

Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review Lee Hooper et al BMJ, doi:10.1136/bmj.38755.366331.2F (published 24 March 2006)

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written by David Marsh, March 26, 2006

McC website
The BMJ editorial was more level handed. However, it should have pointed out that over 50% of the world fish catch goes to animal feed – if we ate less meat, there would be more fish! And that there is a superfluity of small oily fish such as sprats, sild, whitebait, anchovies, sardine, the likes of which are not generally used in the kitchen, yet they are delicious and rich sources of n-3 fatty acids – and minerals.
The editorial should also have mentioned that w-3 DHA is required for nearly every cell\'s membranes which are made from proteins, DHA – docosahexaenoic acid and w-6 AA - arachadonic acid. Without the correct ratio of w-6:w-3 of roughly 2:1 these intricate mesh-like filters don\'t function correctly. The health status of individuals is now being assessed by the degree of integrity of these membranes in red blood cells.
The editorial also failed to mention that it is not only EFA content of fish that is important, but also minerals and traces. Minerals are now predominant in water - having been leached from the land.
Many \'advanced\' civilisations are now considered to be deficient in both long chain EFA\'s and minerals. They are vital not just for cardiovascular system but for the brain and nervous system. As our Chair predicted 30 years ago - the brain will be the next to go. It is already happening, and apparent everyday on our streets.
What we don\'t see so much of is the alarming rise in mental ill health of children who are hidden from our gaze in their homes - or hospitals.
At a time when long chain fats are of vital significance worldwide, this type of research could be considered highly controversial.
Dr Joseph Hibbeln at our recent conference described how the warnings on fish pollution have been wildly overstated, and indeed do not apply to the smaller fish. He described how women in the ALSPAC trial who disregarded the FSA GUIDELINES, HAD BABIES WHICH OUT PERFORMED TIMES 4 the babies born to the women who stuck to the guidelines.
The recent research seems to smell similarly of something equally fishy.

David Marsh.

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