Fish- a danger to health
Almost all of the world’s oceans and rivers are polluted with toxic chemicals, mainly from decades of industrial activity. The health risks from fish and fish oil supplements result directly from this. Oily fish such as salmon, trout, herring, sardines and mackerel are invariably contaminated whilst shark, marlin and swordfish can also contain high levels of mercury. Long-term exposure to these damaging substances is a threat to health.
POP goes the seawall
Persistent organic pollutants (POPs) are particularly nasty and are found in oily fish. POPs come from plastics, paints and pesticides and don’t break down easily in the environment, building up in the food chain. A small fish eats some larvae, then a bigger fish eats the small fish, then an even bigger fish eats that fish, and so on. Fish at the top of the food chain – such as tuna, shark, swordfish, tilefish and king mackerel – have the highest concentrations of POPs. Farmed salmon – which is most of the salmon eaten – are of particular concern because of the concentration of POPs in the feed they eat, mostly wild-caught fish and fish oils.
Although some POPs are now banned, it will be years before they disappear from the environment. Other POPs are still being released. The World Wildlife Fund have expressed concerns that global warming could increase levels of POPs as higher temperatures release chemicals frozen in glaciers.
High levels of POPs in human blood have been linked to insulin resistance and diabetes. Some scientists say resignedly that it is hard to avoid POPs while others believe that they need to be seriously considered when planning treatment. Avoiding fish is one easy way to cut exposure.
PCBs and dioxins
POPs known as polychlorinated biphenyls (PCBs) and dioxins are the main toxins in oily fish. PCBs are widespread, very persistent chemicals and are generally present at low concentrations in fat-containing foods such as milk, meat and fish. Fat-loving, PCBs accumulate in fatty tissue and are particularly likely to be present in oily fish.
Recent surveys have shown that some other fish and crab may also have similar levels of PCBs and dioxins as oily fish. These include: sea bream, turbot, halibut,
dogfish or huss and sea bass.
Implicated in heart disease, cancer and infertility, PCBs and dioxins can also harm developing foetuses by disrupting the growth of male babies’ reproductive organs.
Dioxins were the primary ingredient in Agent Orange, the defoliant sprayed over Vietnam and which has produced an appalling legacy of cancers and other diseases, miscarriages and birth defects.
Mercury is everywhere in the world’s seas and accumulates in the food chain in the same way as POPs. It can affect the kidneys, heart and central nervous system. Exposure for unborn children, where the main organs and nervous system are still developing, is particularly hazardous.
In those studies that have shown fish or fish oils can increase the risk of heart disease, mercury is usually seen as the guilty party as it can accelerate atherosclerosis – the build up of fatty deposits in the arteries.
Men in Eastern Finland eat a lot of fish yet have an exceptionally high death rate from heart disease. In one study, just 30 grams of fish a day was linked to a two-fold increase in heart attacks. Each additional 10 grams a day increased the risk by five per cent. High levels of mercury in their hair indicated that mercury-tainted fish was to blame. Levels of mercury in Finnish lakes are known to be relatively high and it was thought eating non-oily freshwater fish was the cause. It is thought that the mercury simply cancels out any benefit from the omega-3s in fish.
Studies in eight European countries and Israel confirmed that DHA lowers the risk of a heart attack but where high levels of mercury are present, the risk increases. Mercury is already a concern for high-risk groups such as pregnant and breastfeeding women but researchers say that the caution to limit the intake of some fish should be extended to everyone.
The American Heart Association acknowledges the contradictions in research on fish oils and heart health and also points the finger at mercury. It still supports the idea of two weekly servings of fish but says this should be balanced against concerns over pollutants – whatever that might mean! It does support the inclusion of vegetable oils high in ALA as part of a healthy diet. A small move in the right direction.
The Food Standards Agency estimates that over five million people get food poisoning in the UK every year. It is impossible to know exactly how many people are affected as so many cases go unreported.
Most food poisoning is caused by meat, poultry, eggs, dairy, fish and shellfish contaminated with bacteria. Plant foods are much safer as they rarely harbour the types of bacteria that cause food poisoning. When plant foods are responsible, it is usually because they are contaminated with animal excreta, human sewage or prepared with dirty hands.
The role of fish and shellfish in food poisoning is often underestimated. Raw and undercooked fish and shellfish can contain harmful viruses and bacteria.
The Food Standards Agency recommends that elderly people and people who are unwell avoid eating raw shellfish. It also provides an 18-point list of precautionary measures people can take when buying, storing and preparing fish. Of course just avoiding fish and shellfish altogether would be much easier. Indeed excluding all animal foods from the diet will dramatically decrease your risk of food poisoning.
Fish and PhIPs
Some people regularly overcook meat and fish to avoid food poisoning. However, this could lead to even more serious problems.
Grilling, frying or barbecuing meat and fish can produce cancer-causing compounds called heterocyclic amines (HCAs). These dangerous compounds are made when creatine (a chemical found in muscle) reacts with amino acids (the building blocks of protein) and sugar at high temperatures. Meat and fish both contain creatine, vegetables contain none.
The most abundant HCA in food is called PhIP and is linked to cancers of the colon, breast and prostate. Some research suggests that PhIP encourages breaks in our DNA that then lead to cancer. Other work shows that PhIP acts in the same way as the female hormone oestrogen, high levels of which are linked to breast cancer.
This could explain the link between red meat and breast cancer. The amount of PhIP in fish varies widely according to the type of fish and method of cooking; one study reported high levels in grilled salmon. In fact, a recent report from the Physicians Committee for Responsible Medicine showed that the five foods containing the highest levels included: chicken breasts, steak, pork, salmon and hamburgers.
The damaging effect of HCAs can be reduced by foods containing antioxidants, such as vegetables and soya foods. However, the safest option is to avoid meat and fish altogether. Healthier options for grilling and frying include soya burgers, veggie sausages and Portabella mushrooms.