Fishing for FactsWhy public health strategy should promote plant oils in preference to fish oils A scientific report by Laura Scott, MSc Nutrition, Charlie Powell, M.Med.Sci in Human Nutrition, Copyright: The Vegetarian & Vegan Foundation The Vegetarian & Vegan Foundation Contents Introducing Essential Fatty
Acids Essential Fatty Acids and heart
disease Essential Fatty Acids and brain health Contaminated fish are a danger
to health Public perceptions and the misguided
promotion of fish Plant sources – towards a more popular
source of healthy fats 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. Introducing Essential Fatty Acids Not all fats are damaging to health 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 Balancing dietary Essential Fatty Acids 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. Essential fatty acids and heart disease What’s behind the fish recommendations? 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 Fish EFAs vs. Plant EFAs: what does the research tell us? 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. DART – Using Dietary Fish to prevent secondary heart disease 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 GISSI – Using Fish Oil Supplements to prevent secondary heart disease 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 LYON – Using Plant-Derived LNA to prevent secondary heart disease 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. Plant-derived LNA effectiveness of LYON trial confirmed 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. No benefit from fish for low-risk heart disease populations 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 Plant-based diets – great for the heart all round 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 Essential Fatty Acids and brain health 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 n-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. Contaminated fish are a danger to health 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. Dioxins and PCBs in dietary fish and marine fish oils 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 Wild versus farmed – health and nutritional concerns 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. Public perceptions and the misguided promotion of fish Fancy fish? – UK public unimpressed and confused 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 n-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! Promoting fish – A licence to carry on eating an unhealthy diet 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. Plant sources – towards a more popular source of healthy fats 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 in plants protect EFAs 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?
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 & Vegan Foundation (£10 including p&p). The Vegetarian & Vegan Foundation Tel: 0117 970 5190 |
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