02.Benefits and risks
The upside of eating fish
These are some of the important health benefits you get from the omega-3 fatty acids EPA and DHA found in fish.
Heart health There’s now strong evidence that eating fish can reduce your risk of heart disease. Oily fish in particular is a good source of omega-3 fatty acids and eating it regularly can reduce your chances of a fatal heart attack by 25% or more. The National Heart Foundation now recommends we eat two or three serves of oily fish a week. See the table for the fish with the highest levels of omega-3s.
Smarter brains There’s evidence that omega-3s are good for the brain development of infants, even before they’re born. Omega-3s from fish in the mother’s diet cross the placenta, and infants breastfed by mothers who regularly eat oily fish or take fish-oil supplements appear to develop better visual function, which is an indicator of improved brain development. There’s also a growing body of evidence that suggests EPA and DHA may decrease the risk of cognitive impairment and dementia as we get older.
Wider benefits Other potential health benefits from eating fish have been suggested but the evidence isn’t as strong. These include lowering the risk of rheumatoid arthritis and, less convincingly, depression and asthma.
The downside of eating fish
Unfortunately fish, especially oily fish, can contain low levels of highly toxic pollutants, and farmed fish can be contaminated by antibiotics and other chemicals used to control diseases. The toxins of greatest concern are mercury and PCBs.
Mercury This highly toxic metal can affect brain development in children, even at very low levels. It’s found in small quantities in seawater but it accumulates as methylmercury – the most toxic form of mercury – in the flesh of long-lived fish at the top of the food chain, such as swordfish, marlin, shark (flake) and some species of tuna. The New York City Health Department recently analysed blood samples for mercury and other heavy metals and found significantly higher levels in people who ate more fish.
Health authorities advise pregnant women, women intending to become pregnant and children under 16 to limit shark, marlin or swordfish intake to no more than one serve per fortnight – and the rest of us should have no more than one portion a week. These species are also best avoided because they’re not likely to be harvested sustainably. As a rule, small fish are good for small children – and pregnant women.
PCBs and dioxins These chemicals come from industrial pollution and are a known cause of cancer and may be associated with other health risks as well. They’re in many foods, not just fish. In the US, beef, chicken and pork are the biggest food sources of PCBs and dioxins (34%), while fish and shellfish account for only 9%. In Australia, dioxin levels in fish appear to be low, but questions have been raised about dioxin and PCB levels in imported fish.
Chemicals used in aquaculture Fish farmers use antibiotics and other chemicals to prevent disease and parasite infestations. Food Standards Australia New Zealand (FSANZ) has tested for chemical residues in both domestic and imported farmed fish. The tests found the fungicide malachite green in 16% of domestically farmed fish and 17% of imported farmed fish. Testing by the Australian Quarantine and Inspection Service (AQIS) found the antibiotic nitrofuran in some imported prawns. Legally these substances can’t be present in food at any level of concentration, yet FSANZ claims that their findings raise no real public health and safety concerns.
Food imported into Australia is inspected by AQIS, but it tests only 5% of consignments on average. Fish contaminated with prohibited chemicals are rejected, however, 95% of consignments are not routinely tested, nor are most domestically produced fish.
What CHOICE wants
CHOICE wants to see Australian consumers better protected by more extensive and more rigorous testing as in the US, where a government surveillance program repeatedly found malachite green and other banned chemicals (fluoroquinolones, nitrofurans and gentian violet) in farmed seafood from China. The US Food and Drug Administration now requires all shipments of some species of farmed seafood from China to be tested. They’re only released for sale when shown to be free of prohibited substances.