Omega-3

omega-3

Fish is a rich source of omega-3

Omega 3 as a story  has been around for a long time and gets bigger and bigger.  Despite its popularity I get the impression that most people have only the haziest notion of what it is all about.  So let’s have a look at it.  It all began in Denmark in the seventies.  A Danish scientist, Jorn Dyerberg, noticed that Eskimos in Greenland didn’t suffer from heart disease and some other ailments.  But Eskimos in Denmark had much the same health as native Danes.

What was going on?


Dyerberg homed in on diet, and investigated the fats in the blood stream. The body absorbs fat and oil and breaks them down into their constituents, known as fatty acids.  Fish oil contains unusually high levels of a couple of these fatty acids called DHA and EPA.  These fatty acids seemed to be one of the keys to what was going on.  Studies were carried out: chemical analyses performed and data were pored over.
It was, indeed it still is, a confusing area of study where it is hard to untangle cause and effect and get a clear picture of what was going on.  Even Dyerberg produced some results that seemed to contradict his own idea.

As is often the case, it took a while for a picture to emerge.   But it began to look a lot like food rich in DHA and EPA provided protection against heart disease.  There were other health benefits as well, not as well documented, but there did seem to be a pattern.  The chemistry of fatty acids is well known and you could hazard some guesses about what was going on. DHA and EPA are omega-3 fatty acids, which means that at one end of the molecule they have the omega-3 structure that the body needs but can’t make.   It seemed reasonable to suppose that the DHA and EPA were being used by the body to create well functioning tissue structures in the heart.

It wasn’t too big a jump from that to supposing that DHA and EPA might have a generally beneficial effect on delicate tissues like those in the nerves and brain.  Speculations like this are an important part of the scientific process and can be rather fun.  The hard bit is proving them.  Substantiating anything to do with diet is tough.  It is hard to keep track of what people eat and to know what the precise composition of it is.  And there are so many factors out there that can mess up your experiment.  This is shown very well with the publication of a recent study that linked eating fish with reduced risk of heart disease.  It took 19,000 participants – all of whom were physicians – to show up a fairly small reduced risk of heart disease from eating fish.

(Physicians are favourites for studies of this kind.  They avoid a lot of the problems you get from the variability of the wider population.)

But even so, over the decades it has become fairly clear that fish oil as a supplement does offer a modest degree of protection against heart disease.  And there is some evidence of other benefits as well.  It doesn’t seem too big a stretch to suppose that if it is doing the tissues in your heart some good it might well have the same effect on other less easy to study ones.

One of the ideas that I find particularly appealing is that it might help the brain function.  Fish has traditionally been held to be good for the brain (or at least it was when I was growing up). I always like to see folk wisdom being confirmed by hard science.  I can’t say that this particular notion is proved yet.  There hasn’t yet been a really good study with large numbers that finds any benefit.  In fact the most recent properly conducted study I can find showed no effect.  Does this mean the fish oil doesn’t actually work?

I don’t think so.  It is important to look as widely as possible when assessing these things, and look at the whole spread of the literature.  That study was carried out with great diligence. It followed all the rules that ensure reliable results from clinical trials.  But its premise was that a benefit would be found from the specific components in fish oil, i.e., EPA and DHA.   The trouble is the diet contains other omega-3 fatty acids.  The most common is ALA.

If we suppose that the children in the study were getting plenty of ALA in their diet, and that ALA works as well as EPA and DHA then it is little wonder that the fish oil didn’t show any benefit.  Another way of looking at it is that it doesn’t matter too much what form of omega-3 you choose to take.  Fish oil might well be a good source.  But most vegetable oils have a reasonable amount of omega-3 usually in the form of ALA.  Omega-3 is fairly stable, but can be oxidised to less beneficial forms.  So the best sources are ones that are fresh and unprocessed.

So should you make a point of including omega-3 rich foods in your diet, or even to seek out supplements to get more?

I would say that there isn’t a compelling case for doing so if you have basically a healthy balanced diet.  If you eat a lot of highly processed food and don’t eat much in the way of fresh fruit and vegetables then it might be worth considering omega-3 oils in some form as a second best option.  As to the source, fish oils are a good one.  But if you are a vegetarian, have concerns about over-fishing or just don’t much like the taste of fish, omega-3 rich oils like flaxseed are going to be just as good.   But don’t expect miracles.

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References

http://www.ncbi.nlm.nih.gov/pubmed/1163480?dopt=Abstract One of a great many papers by Dyerberg on fatty acid levels.  This one gives details of serum analyses that Dyerberg himself seems confused by.

http://www.sciencedirect.com/science/article/pii/S0891422210000156  A 2010 study of 450 pupils aged 8-10 failed to reveal any improved cognitive ability from EPA and DHA supplementation.

http://www.ncbi.nlm.nih.gov/pubmed/22952185 It takes a huge study with 19,000 participants to reveal a small reduced risk from heart disease associated with eating fish

 

7 thoughts on “Omega-3

  1. Nina

    I do notice a difference when I take fish oil supplements; the skin on my fingers are less dry. There is much less peeling, cracking or blistering compared to the extremely dry state when I’m not on the supplements. Are there studies to link Omega 3 or fish oils to healthier skin?

  2. Tom Walker

    A very balanced article with a conclusion that would be hard to argue against, especially the final “don’t expect miracles”.

    The benefits of eating a sensible, balanced diet make it one of the best investments anyone can make for themselves. It is unfortunately an area that is clouded heavily by the pressures of advertising.

  3. B.

    I’m a vegetarian, and I eat an algae-based DHA/EPA supplement. To be honest, I’m not sure if I’ve seen or felt any physical difference since I started taking it some months ago, but there has been evidence of some improvement in cognitive function in other studies.

  4. Ali

    Aren’t the people of the Mediterranean healthier because of the higher levels of olive oil they ingest? My teflon memory is failing me here. I can’t recall if Omega-3 is present in olive oil.

    Ali

  5. The Stitch and Fold

    I do however remember reading that conversion of ALA (primarily found in n-3 vegetable sources) to DHA (found in fish oil) is quite low, about under 5% in men and slightly higher for women. A quick search on my university library site found a number of articles supporting this, e.g. Thomas (2002), “Efficiency of conversion of -linolenic acid to long chain n-3 fatty acids in man”. Consider that many of the studies of benefits of n-3 have been done using fish oil – then it seems that vegetable sources such as flaxseed are not as potentially beneficial as sources with DHA in it.

    However, there is a potential issue with bioaccumulation of heavy metals in oily fish. In my opinion, the best sources of DHA would be molecularly distilled fish oil, or algal oil such as that mentioned by B.

  6. Seppo

    As the stich and fold mentioned the conversion of ALA to longer-chain DHA and EPA is quite low. I’ve also seen several studies showing the 5% figure (ALA->EPA) for men and somewhat higher for women. The worrisome thing is that the conversion plummets even further down if you have lots of omega-6 fatty acids in your diet. The conversion of ALA to DHA is almost nonexistent in men, as far as I’ve seen in studies.

    I recently looked at the possibililty of getting omega-3 fatty acids from enriched eggs, since chicken are much better at converting ALA to EPA and DHA. When chicken are fed both flax and fish oil the eggs they produce are actually quite high in DHA, sometimes even comparable to some fish oil supplements.

  7. Max

    In so far as the benefits of Omega 3 long chain fatty acids to the brain go, the studies are there. Quite a number actually. What researchers can’t seem to agree upon is whether DHA and not EPA has the most significance in maintaining a healthy brain. Studies by oxford university showed improvements in cognitive ability in children whose diet had been supplemented with DHA while a 2009 paper illustrating evidence from a meta analysis of randomized controlled trials showed that EPA and DHA was responsible in alleviating the symptoms of depression. Treated as a whole (n-3 as opposed to EPA or DHA) then the benefits are a little more clear cut, than when we look at the constituents of the fatty acid themselves.

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