To fish or
not to fish – or to be more precise
to eat fish or not to eat fish – this is most certainly
the question! Eat more fish, eat some fish, eat this
fish, eat that fish – for a food supposedly great
for brains, the subject of fish and diets sure can make
your head hurt! You follow a healthy diet, you exercise
regularly and you don’t eat meat or fish – yet
you turn any page in a health magazine and according
to the latest article, you are doing yourself a disservice
if you don’t eat fish.
This report describes the science behind the flawed oily
fish phenomenon and explains the research the fish industry
does not want publicised - research which clearly shows
that plant-based diets are safer and more protective of
health. The report also describes how the public is unimpressed
and confused by the ‘oily fish mantra’. It explains
how public health strategies which emphasise oily fish consumption
are misplaced and undermine more effective and sustainable
health-promoting solutions. The necessity to eat fish is
exposed as a myth – it’s simply not the health
food the media would have us believe it is.
So what’s the story behind the constant mantra –
fish as part of a healthy diet? It’s the type of fat
found in oily fish - mackerel, salmon, kippers, swordfish,
marlin, herring, sprats, trout, pilchards and fresh tuna
- that is at the heart of this particular tale.
Though most people view dietary fat as quite simply the
original sin, our bodies can’t function properly without
some fat in the diet. But eating the right type of fat is
vital. There are two main types of fat: saturated fats and
unsaturated fats. Saturated fat is found mainly in animal
products like meat and dairy products as well as most processed
foods. Fatty fish, being an animal product is no exception
and 30% of its fat content can be saturated.1
Saturated fat contributes to the risks of heart disease
by boosting blood cholesterol levels and is a damaging and
unnecessary part of the diet.
Unsaturated fat is found principally in plant foods like
seeds, nuts and beans as well as their oils. There are also
two types of unsaturated fats: polyunsaturates and monounsaturates,
both of which play an important role in the diet. Monounsaturated
fats – like those found in olive oil - although not
essential in the diet, are a good replacement for less healthy
fats and may also protect us from heart disease.
Two specific polyunsaturated dietary fats are essential
to good health. This means that they have important biochemical
roles and because they cannot be manufactured by the body’s
chemical processes, they must be taken in food. The essential
fatty acids (EFAs) are linoleic acid (LA) and alpha linolenic
acid (LNA).
LA is known as an omega-6 fatty acid and our tissues can
convert it to give rise to a series of other longer chain
omega-6 fatty acids, for instance AA (arachidonic acid).
LNA is known as an omega-3 fatty acid and in a similar way,
cells in the body can convert it into other longer-chain
omega-3 fatty acid family members, such as EPA (eicosapentanoic
acid) and DHA (docosahexanoic acid). Although AA, DHA and
EPA are physiologically important, they are not strictly
EFAs as they can be made in the body from LA and LNA.
EFAs are important in the normal functioning of all tissues
of the body. They are necessary for the formation of healthy
cell membranes, the proper development and functioning of
the brain and nervous system and for the production of hormone-like
substances called eicosanoids (which include prostaglandins).
Eicosanoids are important regulators of vital body functions,
such as blood pressure, blood clotting, immune responses
and inflammatory responses.
Well documented EFA deficiency in humans is rare. Overt
LA deficiency is seen only when it provides less than 1-2%
of dietary energy, or 2-5g daily for an adult, an amount
which is likely to be provided by even the most meagre diets.2
In severe conditions, symptoms can include dry, cracked,
scaly skin, impaired liver function and decreased growth.3
A specific deficiency state arising from inadequate dietary
LNA has not been demonstrated in healthy humans.4
However, because of LNA’s role as a precursor for
other omega-3 long chain polyunsaturated fatty acids, which
are needed for the development and function of the brain
and retina, it is regarded as a dietary essential.
Also, due to its role in the regulation of blood pressure
and blood clotting, and its ability to reduce blood cholesterol,
it is often recommended that omega-3 polyunsaturated fatty
acids are included in the diet to help protect against coronary
heart disease.
Research suggests that the levels of essential fatty acids,
and the balance between them, may also play a critical role
in the prevention and treatment of a range of other chronic
diseases including, hypertension, arthritis and other immune/inflammatory
disorders, and some cancers.5
The ratio of omega-6 fatty acids to omega-3 fatty acids
is often used to assess the balance between essential fatty
acids in the diet. Over millions of years, humans have consumed
a diet that contained approximately equal amounts of omega-6
and omega-3 essential fatty acids. In Western societies
over the past 150 years, there has been a huge increase
in the proportion of omega-6s consumed in vegetable oils
(both as cooking oils and in processed foods) from the seeds
of corn, sunflower, safflower and soybeans.6
Current estimates of Western diets suggest a ratio of omega-6
to omega-3 fatty acids in the order of 10-20:1.7
Recommendations to increase consumption of omega-3 EFAs
reflect current understanding that a low ratio of omega-3
to omega-6 is linked to increased risk of heart disease.
However, all too often, it is oily fish which are promoted
as being a good source of the omega-3 polyunsaturated fatty
acids. This is in spite of the fact that the richest dietary
sources of LNA are some seed oils (e.g. linseed oil, rapeseed
oil and soya oil) and nuts (particularly walnuts).8
Leafy green vegetables are also a source of LNA.9
Some nutritionists point to the fact that oily fish contains
the longchain omega-3 fatty acids, EPA and DHA in a pre-formed
state, and that these have heart protective properties.
However, promoting fish for this reason ignores the fact
that the body can convert plant sources of LNA into EPA
and DHA. This has been shown by a number of studies which
have demonstrated that plant LNA-rich oils significantly
elevate tissue levels of omega-3 long chain PUFAs.10,
11 Of course if this were not
the case, then millions of non-fish-eating vegetarians across
the world would have increased cardiovascular risk, but
all the evidence points to reduced rates of coronary heart
disease for vegetarians.12, 13
There are simple ways to enhance the conversion of LNA
to EPA/DHA in the body. Diets too high in LA may inhibit
the production of EPA and DHA from LNA. In practice, replacing
oils high in LA like sunflower, corn or soya oil with oils
high in LNA like flaxseed (linseed) or rapeseed (canola)
oil will help the body produce the necessary EPA and DHA.
Affairs of the heart are the primary reason why fish has
come to be viewed as a must-have accessory for a healthy
diet. Fish first got the nutritional thumbs up when it was
observed that populations like the Japanese and Eskimos
with their fish-rich diets have low rates of cardiovascular
disease. The pre-formed EPA and DHA fatty acids found in
fish can help to reduce the likelihood of clots forming
in the blood, help lower blood pressure and cholesterol
levels and lower triglyceride (fat) levels in the body -
all these functions may therefore help to reduce the risks
of heart disease. However, the call to eat fish largely
ignores the fact that EPA and DHA can also be formed in
the body from plant sources of LNA.
A 2002 American Heart Association (AHA) statement explains
that large-scale epidemiological studies suggest that individuals
at risk from Coronary Heart Disease benefit from eating
plant and marinederived omega-3 fatty acids. The AHA recommends
at least two servings of fish per week, especially fatty
fish, as well as plant foods that are high in LNA such as
soyabeans, walnuts and flaxseed. However, the AHA also states
that the recommendations on fish consumption need to be
balanced with concerns over
contamination of fish with environmental pollutants.14
This is an incredibly important proviso and seriously erodes
the idea that fish is ‘healthy’. (See below
for further discussions).
The World Health Organisation (WHO) in its latest report
– Diet, Nutrition and the Prevention of Chronic Diseases
- makes a similar statement that regular fish consumption
(1-2 servings per week) is protective against heart disease.
However, whilst it also states that vegetarians can ensure
adequate intakes of LNA from plant sources, it fails to
give any warnings about the dangers of environmental contamination.15
Much of the promotion of fish as heart-friendly has been
based on evidence from secondary prevention trials. These
trials have investigated whether advising people to eat
fish can prevent a second heart attack from occurring. The
DART and GISSI trials are the two best known studies and
have demonstrated that marine fatty acids significantly
reduce mortality in people who already have cardiovascular
disease. However, much less publicised are the trials that
have looked at the link between plant-derived LNA and the
prevention of secondary heart disease. For example, the
LYON study has demonstrated that eating plant-derived LNA
reduces the risks of secondary heart disease by more than
double that found in the fish-based studies! Let’s
take a closer look at these studies.
The DART trial looked at the effects of dietary intervention
in the secondary prevention of myocardial infarction (MI)
on subjects who had previously recovered from MI. An MI
occurs when blood supply to the heart muscle (the myocardium)
is blocked, which can lead to severe pains in the chest.
The trial found that male subjects who had been advised
to eat about 300g of fatty fish per week had an almost 30%
reduction in overall mortality rate over two years, and
the effect was observed from an early stage. The advice
to increase fish consumption also meant that the subjects
had a simultaneous small decrease in the amount of meat,
meat products, cheese and eggs in their diet.
The researchers believe that the fish oils help normalise
heartbeat rhythms – thus exerting what is called a
beneficial anti-arrhythmic effect. Fish oils also seem to
work on platelet cells found in the blood which ensure that
blood becomes sticky – vital for instance if you cut
yourself and the bleeding needs to be stopped. However,
too much stickiness (clumping), can promote strokes and
heart disease. The EPA in fish oils seems to prevent this
clumping.
Importantly, the study also showed that although there
were fewer fatal heart attacks in the fish advice group,
the total number of attacks was not significantly reduced.16
In essence what this means is that although eating oil-rich
fish may reduce the risk of dying after a heart attack,
they do not necessarily stop another heart attack from occurring.
A follow up DART study by Ness and colleagues assessed
the longterm effect of dietary advice of former DART participants
10 years after the study had first started. Although fatty
fish intake was still higher in those subjects in the original
‘eat fish’ group, the researchers did not observe
any substantial long-term survival benefit in participants
who had been advised to eat more fish.17
The GISSI study similarly looked at the effect of EPA/DHA
on patients who had survived a first heart attack. In this
secondary prevention trial, omega-3 fish oil capsules were
given to those having suffered an MI and who had Mediterranean
dietary habits. Although there was a significant 20% reduction
in overall mortality, the dietary regimen prescribed corresponded
to a very large amount of fatty fish (100g) being consumed
every day.18
The LYON study also looked at how essential fatty acids
can help prevent a second heart attack. The difference however
was that plant-derived LNA was used – not fish or
fish oils. Amazingly, the LYON study achieved a 70% reduction
in mortality – more than twice the reduced risk found
in either the DART or GISSI fish-based trials! There was
also a reduction in significant coronary events in the LYON
study.
The food eaten by subjects in the study was based on the
typical Mediterranean diet, with two grams per day of plant-derived
LNA. Thus participants in the study were advised to eat
a largely plantbased diet: more bread, legumes, vegetables
(both root and green vegetables) and fruit, less meat, with
butter and cream replaced by a plant-based margarine high
in LNA. Although fish intake was encouraged, the experimental
group ate only seven grams more fish than the non-experimental
group leading the researchers to conclude that the favourable
EPA increase seen in the experimental group was due to plant-LNA
intake, not the fish in the diet. The experimental group
also, not surprisingly, were found to have higher levels
of antioxidants – disease-fighting vitamins. Heart
protection afforded by such a plant-based diet was found
to start quickly and also suggested an anti-arrhythmic effect
being responsible for the reduction in heart attack risk.19
Good adherence to the diet was observed and four years on
most people on the original trial were still following the
diet and significantly, heart protection was still being
observed.20
The significance of this plant-based diet research is hard
to overemphasise. Firstly this trial demonstrates that a
diet incorporating plant-derived LNA is clearly superior
to fish-derived EPA/DHA in reducing the risk of death from
a heart attack. Secondly, it shows that plant-LNA also reduces
the risk of having to go through the pain of a second coronary
event. Thirdly, it is clear from long-term followups that
such plant-based diets can be sustained. And fourthly, longterm
heart protection is afforded.
Quite clearly the LYON study has demonstrated that plant-derived
LNA is extremely effective in reducing the risks of secondary
heart disease. Work by Singh and colleagues have further
demonstrated the effectiveness of LNA in reducing total
cardiac events in high-risk populations. A 1997 study looked
at the relative effects of fish oil and mustard oil on subjects
with suspected myocardial infarction. One group of participants
was given 20g of mustard oil/day (giving 2.9g LNA daily)
and another group was given 1.08g of fish-derived EPA/day.
Belching and nausea were two side effects of the fish oil
treatment that led to some subjects leaving the trial. Both
groups showed a significant reduction in total cardiac events.21
In 2002, Singh and colleagues assessed the effect of an
Indo- Mediterranean diet rich in wholegrains including legumes,
fruits and vegetables, coupled with foods high in plant-LNA
from nuts, mustard oil and soyabean oil. This type of diet
was given to a group of patients with risk factors for heart
disease such as angina (chest pains on exertion) and MI.
Those subjects who followed the plant-based diet, rich in
LNA, were found to have a significant reduction in risk
of non-fatal MI and sudden cardiac death. The authors concluded
that omega-3 fatty acids consumed as mustard or soyabean
oils, walnuts, leafy green vegetables and wholegrains, rather
than fish or fish oil supplements, might also reduce the
cardiovascular disease risk in populations that already
consume a prudent low-fat diet.22
As explained below, this concurs with research which has
found no additional heart-health benefits from consuming
fish in populations which are at low risk from heart disease.
Whilst fish may have a part to play in reducing risks of
heart disease in high-risk populations – i.e. those
who have already had a heart attack - the same cannot be
said for low-risk heart disease populations. A systemic
review looking at the role of fish in heart disease by Marckmann
and Gronbaek in 1999 found that fish consumption is not
associated with reduced coronary heart disease mortality
in low-risk populations. They conclude that individuals
at low-risk of heart disease and with healthy lifestyles
do not gain any additional protection for the heart from
eating fish. The authors also question whether the apparent
protection in high-risk individuals is directly caused by
eating the fish itself or whether the link might be explained
by other dietary or non-dietary confounders.23
In total, six of the 11 studies identified by Marckmann
and Gronbaek were unable to conclude that fish consumption
protected against death from coronary heart disease. Some
other research has also questioned the purported protective
properties of fish. Not only did a study in 1997 find no
support for the hypothesized link between fish omega-3 fatty
acids and coronary heart disease risk reduction, the researchers
actually found that consumption of fish omega-3 fatty acids
was associated with up to a 30% increased risk of coronary
death.24 Other more recent research
by Burr et al found that male angina patients given advice
to eat oily fish also had a higher risk of cardiac death,
particularly in those supplied with fish oil supplements.25
In another study, eight out of 11 adolescents experienced
nosebleeds whilst taking fish oil supplements for treatment
of genetically related high cholesterol levels.26
And a systematic review of published papers investigating
whether marine fatty acids can reduce the risk of certain
cancers, like breast and prostate cancer, failed to show
any such beneficial association.27
So who are these low–risk populations? People who
have a low saturated fatty acid diet are considered at lower
risk of heart disease as saturated fat is a known risk factor
for coronary heart disease. Therefore both vegetarian, and
more so vegan, populations are already at reduced risk from
heart disease. Indeed, a recent review stated that vegetarians
have a 25% reduced risk of dying from heart disease than
omnivores.12 In its 2003 position
paper on vegetarian diets, The American Dietetic Association
states that vegetarians are not only at reduced risk from
heart disease, but also have a reduced risk for a host of
other degenerative diseases.13
Having undertaken research which found that vegetarians
and vegans have lower blood pressure than both meat-eaters
and fisheaters, Appleby and colleagues have concluded that
eating fish to lower blood pressure may therefore be unnecessary.28
But not only can a plant-based vegetarian diet reduce the
odds of dying from heart disease in the first place, it
can also offer a therapeutic role in the treatment of heart
disease. Research has demonstrated that a near-vegan diet
can reverse even severe cardiovascular disease and patients
following plant-based diets show a significant reduction
in the hardening of their arteries.29,
30
It is not only our hearts that need EFAs – our brains
do too. The brain is particularly dependent on the EFAs
– over 50% of our brains are made up of these essential
fats.31 Growing brains also need
a one-toone balance of omega-3 to omega-6 fats - it is this
balance that promotes the growth of the cerebral cortex,
the site of intellect and reasoning.32
Based on these facts it is not surprising that fish is also
promoted as essential for infant development and an aid
to overcoming both learning and behavioural problems.
But once again, fish are not the only source of EFAs –
plant-derived EFAs are an alternative source. The obvious
point is that if there was a major problem with a lack of
fish-derived EFAs, then veggie and non-fish eating children
would come bottom in the intelligence stakes. There has
never been any study to suggest this is the case and thousands
of healthy intelligent vegetarian and non-fish eating families
attest to the fact that brains can function perfectly well
without consuming fish!
In particular, much attention has focused on the use of
fish to manage attention deficit hyperactive disorder (ADHD).
However, there is a suggestion that the highly processed
junk food diet that many children subsist on may be the
real cause of behavioural problems. In fact, in their briefing
paper on omega-3 fatty acids, even the British Nutrition
Foundation (BNF) admit, “…at this stage any
link between ADHD and omega-3 fatty acid status should be regarded
as highly speculative”.33
Whilst EFAs may have a role to play, as ever, to argue that
fish is the panacea for combating complex behavioural problems
is far too simplistic.
It’s pretty fair to say that we all buy into the
idea that a healthy environment produces healthy kids; and
that an unhealthy environment produces unhealthy kids. With
fish it’s just the same - thanks to our polluting
activities, the watery worlds of their home environments
are anything but fresh and clean. Fish are literally swimming
in a sea of human waste, but are still marketed as the holy
grail of a healthy diet.
Environmental contaminants stemming from various industrial
processes reach all our waterways - lakes, rivers and ultimately
the oceans. One particularly nasty class of these contaminants
is termed POPs - Persistent Organic Pollutants. These poisons
have become part of many food chains and get more and more
concentrated as they reach each level in the chain. In practice
this means that carnivorous fish like salmon take on the
toxic load of the smaller fish they eat and become ever
more toxic themselves. In turn, humans eat the carnivorous
and potentially contaminated fish like salmon, tuna and
mackerel, believing them to be good for their health! Mercury,
which is also released into the environment by industrial
processes, is another POP and recent studies show that fish
contaminated with mercury are becoming an increasing cause
for concern.
Dioxins and PCBs (polychlorinated biphenyls) are among
the most dangerous chemicals known to man. Dioxins and PCBs
are not only toxic, persistent and bio-accumulative, but
they can also be carried long distances in air currents,
thereby posing a threat to humans and wildlife living in
remote places. Dioxins and PCBs therefore have all the properties
of Persistent Organic Pollutants and are recognised as two
of the 12 agreed “worst” or “most toxic
chemicals known to man”. They are also fat soluble
and found in many foods - oily fish and fish oil supplements
are rich sources of dioxins and PCBs because they accumulate
in fat, and oily fish have large deposits of fat. The toxic
chemicals which fish pick up through the food chain are
often particularly concentrated in their livers, which is
an important fact when weighing up the benefits of fish
liver oil supplements.
The potential human health effects of these chemicals may
include some cancers, damage to the immune system, infertility,
birth defects, and altered levels of sex hormones.
Back in 1995, Greenpeace scientists sampled 22 brands of
fish oils, 17 of which were sold in health food shops as
dietary supplements. Of the 22 sampled, 21 contained high
levels of hazardous contaminants, namely the organochlorine
pesticides DDT, and lindane, and PCBs.34
Greenpeace reported that anyone taking the recommended dose
of the worst contaminated oil capsules, obtained from Norwegian
salmon, would receive 128 times the UK estimated daily intake
of PCBs.
In 1997, the Ministry of Agriculture, Fisheries and Food
(MAFF) conducted the first Government survey of dioxins
and specific PCB congeners in dietary supplements and medicinal
products containing fish oils. MAFF concluded that, “the
results confirm earlier reports of relatively high concentrations
of these contaminants in fish oils, particularly fish liver
oils”. MAFF also noted that consumption of contaminated
fish oils could give rise to exposures above the WHO Tolerable
Daily Intake (TDI).35
MAFF conducted its first comprehensive survey for dioxins
and PCBs in 132 samples of marine fish in 1999. All 132
fish samples analysed (cod, haddock, plaice, whiting, red
fish, herring, mackerel, salmon and fish fingers) contained
dioxins and PCBs.36 A World Wildlife
Fund commentary on the findings of this survey concludes
that the concentrations of dioxins and dioxin-like chemicals
found in the samples were at a level which meant that some
of the EU fish-eating population, particularly children,
would regularly exceed the WHO TDI.37
Also following this research, the Committee on Toxicity
of Chemicals in Food, Consumer Products and the Environment
(COT) recommended that people should only consume on average
one portion of oily fish each week to ensure that the “majority”
of individuals do not exceed maximum recommended levels
for dioxins and PCBs.36
Recent surveys carried out in 2002 by both the UK Food
Standards Agency (FSA) and the Food Safety Authority for
Ireland (FSAI) confirm that fish oils still contain detectable
levels of dioxins. The FSA found that 12 of 33 samples of
branded fish oil supplements bought from UK retailers contained
concentrations of dioxins which exceeded the European Commission’s
limit for dioxins in fish for human oil consumption (2ng/kg
limit in fish oil for dioxins, in effect from 1 July 2002).38
The Irish study found that 10 out of 15 top selling brands
of fish oil and fish liver oil capsules exceeded the new
European dioxin level limits and in one case, the dioxin
level was five times this maximum limit.39
In an October 2002 article entitled “Fish - what’s
the catch?”, the Consumers’ Association added
its caution to the growing numbers warning about contaminants
in oily fish. The Consumers’ Association reported
that eating more than one portion of oily fish a week increased
the chances of exceeding the TDI for dioxins and PCBs, and
they estimated that as much as a third of the UK population
was exceeding the TDI for PCB contaminants. Their report
went on to warn that the high levels of dioxins and PCBs
found in the FSA 2002 survey could “put millions at
risk”, especially in light of the Consumers’
Association own survey findings that a fifth of people who
eat fish also took a daily fish oil supplement.40
The total fish oil market accounts for two percent of the
total world fat and food oil production. Fish oils are used
widely by the European baking industry and their use is
also widespread in the
manufacture of products such as biscuits, margarine and
ice cream. Greenpeace suggest that the food industry use
of fish oils in the manufacture of foods is another route
by which people can take in toxic chemicals.41
According to COT (The Committee on Toxicity of Chemicals
in Food, Consumer Products and the Environment), methylmercury
(organic mercury) in fish makes the most significant contribution
to dietary exposure to mercury. Mercury is a poison that
is known to affect the kidneys and central nervous system
(CNS).42
Following a comprehensive 2003 survey on the level of mercury
contamination in fish by the Food Standards Agency (FSA),
the Agency advised that “pregnant and breastfeeding
women, and women who intend to become pregnant, should limit
their consumption of tuna…..and avoid eating shark,
swordfish and marlin”. The basis for this advice is
the fear that mercury can harm the developing nervous system
of an unborn child. The FSA advice goes on to state that
children under 16 should also avoid eating shark, swordfish
and marlin and that other consumers should eat no more than
one portion a week.43
The FSA survey showed that almost all fish eaten contains
detectable levels of methylmercury and that dietary exposure
estimates for some consumers were close to or exceeded safety
guidelines. The three species with the highest mercury content
were shark, swordfish and marlin, having mean mercury levels
of 1.52, 1.36 and 1.09 mg/kg respectively. These are above
the safety levels defined by European Community (EC) Regulation
221/2002 which is 0.5mg of mercury/kg for fish in general
and 1.0mg/kg for these larger predatory fish. Fresh tuna
contained 0.40mg mercury/kg, whereas canned tuna contained
0.19mg/kg.43
Alongside maximum levels of mercury set for fish, the WHO
has set figures for humans. The WHO recommendation is that
a Provisional Tolerable Weekly Intake (PTWI) of 0.3 mg total
mercury should not be exceeded, of which no more than 0.2
mg should be present as methylmercury in a 60kg adult, equivalent
to 3.3 mg/kg bodyweight.
One study by Storelli and colleagues has sought to determine
mercury levels in tuna caught in the Mediterranean sea and
calculate from this whether the PTWI could be exceeded.
In this study, average total mercury concentrations were
1.18mg/kg wet weight in bluefin tuna and the total mercury
concentrations exceeded the maximum level fixed by the EC
in over 60% of the bluefin tuna analysed. The estimated
weekly intake of bluefin tuna in this population would mean
that the PTWI was far exceeded.44
The Storelli team has also found other edible fish in the
Mediterranean to be similarly contaminated with mercury.
The authors conclude by stating that mercury intake via
the consumption of some fish species could be a matter of
concern.45 In view of these and
other studies, researchers in the field stress that mercury
in fish must continue to be monitored closely in order to
assess risks of mercury contamination.46
To confuse the issue further, different countries give
varying advice about mercury-contaminated fish. Officials
in Sweden are so concerned about mercury contamination,
that official advice states that women should eat no more
than one portion a month of oily fish caught in certain
places.40
Research published in 2003 in the Environmental Health
Perspectives journal found that a high proportion of 116
subjects identified as being high fish consumers had blood
mercury levels which exceeded the maximum safe level (5ug/l)
recommended by the US
Environmental Protection Agency and National Academy of
Sciences. Interestingly, within 41 weeks, the blood mercury
levels in 65 of 67 subjects who reduced their fish intake
fell below this threshold.47
This research contrasts well with a study commissioned
by MAFF in 2000 into dietary exposures of vegetarians to
metals found in food. This study failed to detect any mercury
at all in the sampled vegetarian diets. MAFF concluded,
“it is reasonable to assume that because the participants
in this study did not eat fish, their dietary exposures
to mercury will be substantially less than those of the
general population”.48
Mercury contamination in fish could also very well limit
any heart disease risk reduction benefits supposedly arising
from the EFAs they contain – the major reason oily
fish are promoted in the diet in the first place!
In 1995, Salonen demonstrated that a high intake of mercury
from eating non-fatty fish, and the subsequent mercury accumulation
in the body, are associated with an increased risk of myocardial
infarction (MI), as well as death from coronary heart disease.
An average daily fish intake of 30g or more was associated
with a twofold increase MI risk. For each additional 10g
of fish intake per day there was an increment of five per
cent in the five-year risk of MI. No surprise that the authors
of this study concluded by stating that fish may contain
agents not so healthy to the human cardiovascular system.49
A paper published in 2002 by Guallar and colleagues further
examines the possibility that mercury increases the risk
of cardiovascular disease. Mercury may predispose to heart
disease by promoting the production of free radicals - unstable
molecules that damage body cells. Guallar’s team found
that mercury levels were directly related to risk of MI
and concluded that the risk of heart disease in a population
may depend on the balance between omega-3 fatty acids and
the methylmercury in fish consumed. The Food and Drink Administration
(FDA) in America have also advised that high-risk groups
such as pregnant women do not eat fish with high levels
of mercury like swordfish and shark. The authors of this
report say their results raise the possibility that this
advice be extended to the general adult population too.50
Mercury is also implicated as a possible cause of infertility.
A recent study has revealed that higher blood mercury concentrations
are associated with both male and female infertility. Choy
and colleagues found that when compared with fertile couples,
infertile couples had significantly higher blood mercury
levels. What this work also revealed was that within the
infertile population itself, those eating more seafood had
elevated levels of mercury in the blood. The researchers
concluded by stating that “reduction in dietary consumption
of seafood is a measure that may be effective in controlling
the accumulation of mercury”.51
Due to pressures of over-fishing, a greater proportion
of fish now eaten is from farmed fish. In fact fish farming
is the world’s fastest growing sector of food production.
In addition to ethical and environmental implications (including
nutrient and chemical pollution and harmful impacts on wild
fish populations)52, there are
also health and nutritional concerns in relation to eating
farmed fish. Whilst oily fish are promoted as heart-friendly
on the basis of their fatty acid profile, there are important
differences between farmed and wild fish. Farmed salmon,
for instance, can contain two to three times less of the
heart-healthy omega-3 fats as well as 15% less protein.
Farmed fish can also contain chemical pesticide residues
as well as dangerous levels of toxic man-made chemicals
like polychlorinated biphenyls (PCBs).53
A 2002 study into preliminary examinations of the chemical
contaminants of edible fish makes for worrying reading.
Researchers have found that farmed salmon show higher levels
of PCBs, organochlorine pesticides (OPs) and polybrominated
diphenylethers (PBDEs) than wild salmon. In fact, the farmed
salmon had 10 times greater toxic potential than wild salmon.
The most likely explanation for this was that the feed given
to farmed salmon – fish oil and fishmeal – was
itself contaminated with these chemicals from industrial
pollution of the sea.54
Research conducted by the Environmental Working Group (EWG),
published in August 2003, found that on average, farmed
salmon, had 16 times the dioxin-like PCBs found in wild
salmon. A sample of Scottish salmon was found to have the
highest levels of PCBs of all the salmon tested. The EWG
noted that in addition to contaminated fishmeal, farmed
salmon are intentionally fattened and can therefore accumulate
more PCBs than wild salmon.55
In fact, health fears about farmed fish never seem to be
far away, whether it’s PCB contamination, the excess
use of antibiotics or the administering of additive fish
colouring pigments (like canthaxantin, which is banned for
direct human consumption). One of the most recent concerns
has revolved around the detectability of a banned fungicide
residue, suspected of causing genetic mutations that can
lead to malignant tumours in humans. More than a year after
being banned, 19% of salmon sampled by the Government’s
Veterinary Medicines Directorate tested positive for the
fungicide Leuco Malachite Green.56
And yet another concern came to light in June 2003 when
Greenpeace published results of a study, undertaken by Southampton
University, which found that nuclear waste was found in
supermarket salmon. The study found that four out of seven
tested samples of farmed smoked salmon on sale in leading
British supermarkets contained detectable levels of radioactive
Technetium-99 waste. Greenpeace concluded that nuclear pollution
from Sellafield was contaminating Scottish farmed salmon.57
So, farmed fish are very far from the environmentally friendly
and safe choice we are led to believe they are – and
from a health perspective, when fish are farmed they lose
some of their protective EFAs. All in all a new alternative
is needed to supply EFAs in the diet.
Despite the constant message that fish is a healthy and
necessary part of the diet, the UK public just don’t
buy it – metaphorically speaking as well as literally!
According to the FSA’s 2002, National Diet and Nutrition
Survey of Adults Aged 19 to 64 Years, average oily fish
consumption is only 53g a week, representing only about
a third of a single portion. This meagre quantity falls
well short of the Agency’s advice for people to eat
two portions of fish a week, one of which should be oily
(a portion is approximately 140g). This is also a tiny amount
compared to the 200-400g weekly intake of oily fish that
have been administered to produce heart benefits in research
studies. And in any case, only four out of 10 men (41%)
and less then half of women (47%) eat any of the oil-rich
fish that provide the healthy EFAs.58
Quantitatively, fish is far from being the most significant
overall source of omega-3 fatty acids in the British diet.
Compared to the 14% contribution of total omega-3 fatty
acids in the average diet, both vegetables and cereal products
are more important dietary sources, contributing 22% and
17% respectively.59
In a recent paper, Mantzioris and colleagues discuss the
ineffectiveness of recommendations to increase fish consumption.
They explain that as modern Western societies consume little
fish, an increase in fish consumption to the levels advised
would involve major dietary changes. In conclusion they
state, “this dietary approach is not an effective
way to achieve an increase in the consumption of omega-3 fatty
acids at a community or clinical level”.60
Thus, from a public health point of view, encouraging the
general population to eat fish in order to gain healthy
amounts of EFAs is simply not working. Fish are a high maintenance
food – they go off quickly, are greasy and smelly
and in some people can cause stomach problems. With their
nice little side order of possible toxic chemicals, fish
need one heck of a PR guru! But they had better start soon
for many species are facing imminent extinction –
and won’t be around for a quick makeover session with
the spin-doctors for very long. And as we have seen, farmed
fish is not the solution.
The issue of environmental contamination of fish is the
principal reason why the FSA from time to time change their
recommendations on how much, who should and who shouldn’t
eat what types of fish. However, the FSA advice is sometimes
far from clear and it is easy to find statements which are
contradictory. For instance, advice on the FSA website is
clear that two portions of fish should be eaten weekly.61
However, the FSA leaflets entitled “Fish and shellfish”
and “Mercury in fish: your questions answered”,
advise that at least two servings of fish should be eaten
per week.
And when it comes to oily fish, public confusion reins!
A 2002 Consumers’ Association survey found that only
a sixth of fish eaters knew the FSA advice to eat oily fish
once a week and most people were confused by what was meant
by oily fish (14% thought that cod was an oily fish!). More
than half thought the advice was to eat two or more portions
per week and 61% had no idea that oily fish may contain
contaminants. The Consumers’ Association reports that
the FSA was unable to provide any clear answers about the
health implications of eating more than one portion per
week. They also criticise the FSA for not providing any
guidance about what constitutes a portion. Just as alarming
is the fact that no-one surveyed could give details of the
FSA advice about mercury and fish and nobody could name
any of the fish which pregnant women, breastfeeding women
and children were advised to avoid.40
So, not only are the UK public not interested in eating
fish in the amounts recommended, the guidance itself is
unclear and misunderstood, and in any case little known.
Public confusion rules the day!
Marckmann and Gronbaek have demonstrated that fish is not
a necessary part of the diet for people who are at low-risk
of heart disease.23 It is therefore
surely better to combat heart disease by encouraging a heart-friendly
diet in the first instance – a plant-based diet. Many
people following the current FSA recommendation to eat two
portions of fish a week, including one oily portion of fish,
may be misleadingly reassured that this ‘health-promoting
panacea’ permits them to carry on with their saturated
fat-laden diets – after all, that side order of oily
fish will keep the heart happy! Or else, why not pop a fish
pill rather than make changes towards a healthy diet? So,
promoting fish as ‘heart friendly’ could actually
deter individuals from making the fundamental dietary changes
necessary for real long-term heart and body health. Dietitian
Sandra Hood puts this succinctly when she states that “the
consumption of fatty fish is encouraged as a form of damage
limitation”.62 A far healthier
and simpler solution would be to promote a more plant-centred
diet that included EFA-rich seeds, nuts and oils. Plants,
not fish, are the way forward for health.
If you invented a wish list for an EFA-containing food
it would probably read something like this. First and foremost,
it would need to be EFA-rich and heart-friendly. Just as
importantly, it would need to taste good, be versatile in
the kitchen, be environmentally sustainable (so it could
be cultivated), not go off too quickly (or come ready-packaged
with a protective skin), be less likely to be environmentally
contaminated by pollutants like PCBs or mercury, be easily
handled (so it didn’t make your hands greasy) and
be nonsmelly. Pretty tall order you might think for a food.
But plant sources of EFAs fulfil all these criteria and
more – think nuts, seeds, beans and green leafy vegetables.
Brown and red algae are now even being grown commercially
for EPA and DHA.63
Humble nuts and seeds are also true wonder foods. They
are EFArich, can be grown for indefinite harvests and come
protected in a shell or seed. According to one of the world’s
experts on EFAs, LNAcontaining seeds are available in fresher
conditions than fish oils (because they are simpler to produce),
are much less likely to be contaminated with pollutants
and are also more stable (coming ready-packaged with the
antioxidant vitamin E).64 Additionally,
of course from studies like the LYON trials, plant-derived
LNA is known to be heart healthy. Plant sources of EFAs
have huge advantages over fish sources of EFAs and yet are
ignored by nutritionists intent on promoting fish to an
unimpressed public.
Antioxidants, such as vitamins C, E and beta-carotene (the
precursor of vitamin A) are the body’s main defence
against free radicals (for instance, the mercury found in
fish) and are found abundantly in plant foods like fresh
fruits, vegetables, seeds and nuts. But antioxidants are
vital for another important function – a function
that demonstrates why plant sources of EFAs win hands down
nutritionally over fish-derived EFAs.
EFAs spoil very easily, but antioxidants help to slow down
the decaying process. This can be evidenced most delightfully
if you happen to pass a fish stall – that ‘fishy’
smell is an indication that the EFAs present in the fish
are starting to putrefy! Plant sources of EFAs like seeds
and nuts naturally come ready-packaged with the antioxidants
needed to stop them going off – in particular vitamin
E. It’s a bit like one of those special offers you
get at the supermarket – ‘buy one get one free’.
Eating seeds or nuts means you are buying the beneficial
EFAs and getting their natural protector (vitamin E) free,
all in the same neat package. Not so if you choose to get
your EFAs from fish as fish is not a source of vitamin E.
As an ironic twist of fate, balanced vegetarian diets, and
even more so vegan ones, supply far more of these protective
antioxidants than your typical omnivorous diet 65
– but since the veggie diets eschew some of the harmful
foods like meat and fish they probably need these vitamins
less in the first place!
So, what exactly are the better alternatives to fish-derived
EFAs?
Plant sources of EFAs
Food (serving size) |
Omega-3 (g) (LNA) |
Omega-6 (g)(LA) |
Oils |
|
|
Flaxseed (linseed) oil, 1 tbsp |
8.0 |
2.2 |
Rapeseed (canola) oil, 1 tbsp |
1.3 |
2.8 |
Walnut oil, 1 tbsp |
1.4 |
7.2 |
Soy oil, 1 tbsp |
0.9 |
6.9 |
Wheat germ oil |
0.9 |
7.5 |
Nuts and seeds |
|
|
Flaxseeds (linseeds), ground, 2 tbsp |
3.2 |
0.8 |
Walnuts, 2 tbsp |
1.0 |
5.4 |
Vegetables, Fruits and Legumes |
|
|
Soybeans, cooked, 1 cup |
1.1 |
7.8 |
Tofu, firm, 1/2 cup |
0.7 |
5.0 |
Tofu, medium, 1/2 cup |
0.4 |
2.9 |
Soy milk, 1 cup |
0.4 |
2.9 |
Berries, 1 cup |
0.2 |
0.2 |
Peas, 1/2 cup |
0.2 |
0.2 |
Legumes, 1/2 cup |
0.05 |
0.05 |
Green leafy vegetables (broccoli, kale, Brussels sprouts,
leeks, spinach, Chinese greens, salad greens, 1 cup
raw or 1/2 cup cooked |
0.1 |
0.03 |
Grains |
|
|
Oat germ, 2 tbsp |
0.2 |
1.6 |
Wheat germ, 2 tbsp |
0.1 |
0.8 |
Note: 1 cup = 112g
Sources: US National Institutes of Health, EFA Education
website66
Davis B., Essential Fatty Acids in Vegetarian Nutrition67
The Physician’s Committee for Responsible Medicine
statement on Essential Fatty Acids states that good sources
of omega-3 fats should be included daily in the vegetarian
diet.68 As the table on page 22
demonstrates, LNA is found in many seeds, nuts, grains and
legumes and more concentrated sources can be found in oils
such as, flaxseed (linseed), rapeseed (canola), soybean,
walnut, and wheat germ. The UK Committee on Medical Aspects
of Food Policy (COMA) recommends that the energy derived
from omega-3 polyunsaturated fatty acids is at least 0.2%
of total energy intake for individuals.4 A woman consuming
2000 calories (kcals) could achieve this minimum recommendation
by consuming only four calories or 0.4g of LNA daily. The
corresponding figures for a man consuming 2,500 calories
would be 5 calories and 0.6g of LNA. However, a UK Dietary
Reference Value for LNA based on a population average has
not been set. Some nutritionists suggest that vegetarians
who do not consume preformed EPA and DHA, should consume
one per cent of their energy needs as LNA, equating to 20
calories or 2.2g for an adult consuming 2000 calories a
day.67 This recommendation is
in line with the WHO 2003 population nutrient intake goal
for omega-3 PUFAs of one to two per cent of total energy.15
Again, although no definitive recommendations exist, because
of the importance of long-chain omega-3 fatty acids in the
developing foetus and infant, it may be appropriate for
pregnant and lactating mothers to further increase their
intakes of LNA. The following plant foods provide the WHO
recommendation to eat a minimum of 2.2g LNA per day: - one
teaspoon flaxseed oil, one tablespoon flaxseed (flaxseed
is also known as linseed and is best ground immediately
before consumption), a quarter of a cup (28g) walnuts.69
All these foods are easily available from supermarkets.
In fact many other ordinary and everyday vegetarian foods
also contain LNA, contributing towards the daily requirement.
For instance, half a 450g tin of baked beans contains 0.4g
LNA, a 50g packet of peanuts contains 0.18g LNA and even
a 30g packet of crisps contains 0.1g LNA!70
A deficiency in omega-6 is highly unlikely as it makes
up a large proportion of most vegetable oils present in
the diet, for instance, 71% of sunflower oil, 76% of safflower
oil and 57% of corn oil. These oils are used in most processed
foods, frozen foods, margarines, French fries, potato chips
and bakery products.
In 1991, COMA recommended that the population average intake
of omega-6 polyunsaturated fatty acids should be 6.5% of
food energy intake.4 For an adult consuming 2,000kcal daily,
this represents 130kcals or about 14g. However, a further
recommendation was made by the Committee in its Report on
Nutritional Aspects of Cardiovascular Disease, that there
should be no further increase in average intakes of omega-6
polyunsaturated fatty acids and that individual intakes
should not contribute more than 10% of energy.71
A diet high in omega-6 fatty acids inhibits the production
of EPA and DHA from LNA. A ratio of LA to LNA of 4:1 or
less has been shown to be optimal for the conversion of
LNA to EPA and a fatty acid ratio of this order is recommended
by nutritional experts.72 Alarmingly,
current estimates of the omega-6 to omega-3 fatty acid ratio
in Western diets are in the order of 10-20:173
To ensure an adequate intake of LNA, good plant sources
should be included in the daily diet (see p. 22 & 23),
including green leafy vegetables, seeds, whole grains, beans
and nuts. One of the best sources is flaxseed oil, containing
57% omega-3 and 17% omega-6 fatty acids. Minimising consumption
of omega-6 rich vegetable oils (especially corn oil, sunflower
oil and safflower oil) and commercial oil-based processed
foods will also help increase the omega 3 to omega 6 dietary
ratio.
The best way to buy and store nuts, seeds and their oils
is in very small quantities and to keep them in the fridge.
This helps to ensure that they are as fresh as possible.
These oils are not suitable for heating as it destroys the
beneficial EFAs. These are best used as a cold salad dressing.
Most health food shops and supermarkets sell packets of
nuts and seeds and blended plant oils - usually marketed
as oils rich in omega-3 and omega-6 fats. They usually contain
information on how much oil to use each day.
In addition to keeping omega-6 fatty acids at a modest
level, a good approach is to make monounsaturated fatty
acids the largest portion of fat in the diet – olive
oil is 77% monounsaturated fat. Consumption of saturated
fatty acids (and trans fatty acids in processed foods) should
also be limited as they are unnecessary in the diet, they
are a major risk factor for atherosclerosis and they can
interfere with the conversion of LNA into DHA.
To eat fish therefore I am healthy. This is the prevailing
message with which we are constantly bombarded. Sold as
the ‘magic bullet’ that will cure all our ills,
fish consumption is now seen as the ultimate must-have health
food accessory. And few people ever question this wisdom
– yet as research shows, eating fish is most certainly
not a guarantee of good health. True, fish are a source
of essential fats necessary in the diet but they are not
the only – or healthiest – source. Fish are
also a source of unhealthy and unnecessary saturated fat
in the diet. Plant-derived essential fats are a far superior
source of good fats in the diet.
Environmental contamination of the oceans now means that
when you take a mouthful of fish you are taking a mouthful
of poison – most likely mercury or PCBs. Worth the
risk you may feel if your heart gets protection? Yet if
there was a food source that gave your heart double the
protection that afforded by fish and didn’t come laced
with poisons what would be the sensible choice? Not a particularly
tough question! Plant-derived EFAs have numerous advantages
over fish-derived EFAs yet are virtually ignored by health
professionals.
The incorporation of fish into the average, highly saturated
fat and processed diet, will not provide the health benefit
that many believe it will. The way forward for health is
to adopt a more plant-centred diet low in saturated fat
and high in healthful essential fats. Vegetarian and vegan
diets plentiful in EFA-rich foods like nuts and seeds are
the diet of choice, not only in helping to combat heart
disease but also in combating many other degenerative diseases.
Fish is far from the healthy food it is marketed as. Our
hearts don’t need fish, our brains don’t need
fish and our health is far better served by plant EFAs and
a well balanced plant-based diet.
Fully referenced copies of this report are available from
the Vegetarian and Vegan Foundation (£10 including
p&p).
The Vegetarian & Vegan Foundation
Top Suite
8 York Court
Wilder Street
Bristol
BS2 8QH
Tel: 0117 970 5190
Fax: 0117 924 4646
Web: www.vegetarian.org.uk
Email: info@vegetarian.org.uk
|