Dear Liz, and others
This story questioning benefits of omega-3 oils appeared in the UK media a
few days ago, but didn't 'run'. Your links refer to 2 though separate
topics, though there is a connection, and should be commented on separately.
The first link, the British Medical Journal one, refers to an editorial in
the journal which comments on a paper which questioned some claimed benefits
the omega-3 oils and let me comment on that first.
The paper is Hooper et al., 'Risks and benefits of omega 3 fats for
mortality, cardiovascular disease, and cancer: systematic review'. It has
not appeared in print yet, but a pdf file of it can be downloaded from
http://bmj.bmijournals.com .Go to the site and enter hooper and omega 3 into
the author and keywords boxes respectively in the top right and the paper
and its link to the pdf file will be listed. It describes a meta-analysis of
a large number of studies of the risks and benefits stated in the title.
Their conclusion from this pooling and analysis of data was not the same as
some previous meta-analyses, but those previous ones did not include the
results of a recent large study. Let me quote the conclusion from the
summary of the paper:"Long chain and shorter chain omega 3 fats do not have
a clear effect on total mortality, combined cardiovascular events, or
cancer." Within the paper is an highlighted box which I assume was inserted
in the editorial process to catch the eye of the skimming reader. Here is
what this box states under a subtitle 'What this study adds': "This
systematic review assessed the health effects of long chain and shorter
chain omega 3 fats (together or separately) on total mortality,
cardiovascular events, cancer, and strokes in a wide group of participants
and found no evidence of a clear benefit of omega 3 fats on health" Note
that this editorial embellishment has changed the authors' '... do not have
a clear effect on total mortality, combined cardiovascular events, or
cancer.' to '...found no evidence of a clear benefit of omega 3 fats on
health'. These 2 conclusions are not the same and that of the authors of the
paper are more cautious and limited in scope than the editorial box suggest.
The authors are quite explicit that they did not set out to examine claims
for the health effects of omega-3 acids generally, but for some specific
aspects of health, mortality, cardiovascular disease and cancer.
It is a highly technical paper directed towards epidemiologists and can only
be appreciated by specialists, but the reasonably informed person can follow
the discussion. The authors discuss at some length the recent survey which
swung their meta-analysis towards a no effect compared with previous
analyses that did show an effect. The authors write in the section
Interpretation: "It is not clear whether long chain or short chain omega 3
fats (together or separately) reduce or increase total mortality,
cardiovascular events, cancer, or strokes. Our findings do not rule out an
important effect of omega 3 fats on total mortality, as robust trials at low
risk of bias reported few deaths.". They also write: "UK guidelines
encourage the general public to eat more oily fish, and higher amounts are
advised after myocardial infarction (supported by trials after myocardial
infarction). This advice should continue at present but the evidence should
be reviewed regularly. It is probably not appropriate to recommend a high
intake of omega 3 fats for people who have angina but have not had a
myocardial infarction." These observations is not quite the clear-cut
conclusions put out in the media in Britain.
The first link in Liz's message is to an editorial in The BMJ of 24 March
which is probably the source of the press release because the Hooper et al.
is not yet published. Though called an Editorial it is more like a
scientific paper rather than an editorial in a newspaper in that it cites
references in a bibliography and is signed. After briefly summarising the
conclusions of the Hooper et al paper it goes on to discuss health benefits
of consumption of omega-3 oils other than on cardiovascular conditions. It
is the last paragraph that to my mind is incorrect and contentious; I should
quote it in full: "We are faced with a paradox. Health recommendations
advise increased consumption of oily fish and fish oils, within limits, on
the grounds that intake is generally low. However, industrial fishing has
depleted the world's fish stocks by some 90% since 1950, and rising fish
prices reduce affordability particularly for people with low incomes. Global
production trends suggest that, although fish farming is expanding rapidly,
we probably do not have a sustainable supply of long chain omega 3 fats.".
For the claim that the world's fish stocks have been depleted by some 90%
since 1950 the author cites a paper by Myers RA,& Worm B., 'Rapid worldwide
depletion of predatory fish communities', Nature, 2003, 423:280-3. This
paper is not available at the Nature site unless you have a subscription to
the journal, but can be downloaded from the Berkley university site at
http://seismo.berkeley.edu/~manga/eps3/myersandworm2003.pdf. This paper
though is about depletion of stocks of predatory fish, not of stocks of fish
generally. Predatory fish are not fished directly for fish meal and oil
though both these products are obtained from wastes from processing of
predatory fish, for example meal from fillet waste, oil from livers. Most
fish oil is obtained from directed fisheries of pelagic fish. Over the last
two decades or so the catch from industrialised fisheries has been around
25-30 million tonnes/year other than in El NiZo years compared with about 4
million tonnes of waste material going for reduction. FAO publishes on
bi-annual basis a "The State of World Fisheries and Aquaculture" and as I
read them they do not express great concern for the status of pelagic stocks
caught for industrial purposes. It seems to me from my reading, though
without specialised knowledge of the subject, that there is a sustainable
supply of marine-sourced omega-3 fatty acids. What is up for discussion
whether or not this sustainable production is adequate for all requirements,
and how much is to be used in animal feeds and how much for human
consumption.
The author of the editorial has a point about affordability. In the UK
anyway, fillets, skin-on, of predatory white-fleshed fish such as cod
retails at around 20USD/kg, more expensive than chicken or of common cuts of
pork or beef. Farmed salmon is slightly cheaper, about 17USD/kg. Salmon is
very much richer in omega-3 acids than gadoids, fillets anyway, so farmed
salmon is a much better buy if omega-3 intake is of concern. Pelagic fish,
herring and mackerel, on a fillet basis, are a little cheaper still, but
still more expensive than chicken or cheaper cuts of red meat. Official
health guidelines recommend that we consume one portion a week of fatty
fish. Assuming a portion is 150g of fillet and a world population of 6
billion, this would require 100 million tonnes live weight of oily, that is
predominately pelagic, fish. Total world fishery production of all sorts of
aquatic animals for all outlets, human consumption and for reduction, is
around 130 million tonnes, insufficient for all persons in the world to have
one helping of fatty fish a week even if all the pelagic fish going for
reduction is diverted to human consumption. Now that is the paradox.
Peter Howgate
----- Original Message -----
From: "Liz Brown" <bfeab@uaf.edu>
To: "seafood" <seafood@ucdavis.edu>
Cc: "Laine Welch" <msfish@alaska.com>; "Bristol BayTimes"
<bbtimes@nushtel.com>; "Victoria Briggs" <ViedeF97@aol.com>
Sent: Thursday, March 30, 2006 4:30 PM
Subject: dissing omega 3
> Here's the first 'not all it's cracked it up to be' story I've seen about
> omega 3:
> http://bmj.bmjjournals.com/cgi/rapidpdf/bmj.38798.680185.47v1?hrss=1
>
> Here's a link to the source for the assertion that we should stop eating
> fish because we've depleted the world's stocks:
> http://www.nature.com/nature/journal/v423/n6937/full/nature01610.html
>
> My knee jerk reaction is that this is irresponsibly ignoring that many
> fisheries are managed sustainably. I would be interested in hearing other
> perspectives.
>
> --
> Liz Brown
> Marine Advisory Program
> University of Alaska Fairbanks
> PO Box 1549
> Dillingham, AK 99576
> 907-842-1265
> Fax 907-842-3202
> www.uaf.edu/map
>
>
>
>
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