Earlier this year a scientific paper reported hazardous substances in farmed salmon. Within hours, the headlines were warning us that we should be feeling fishy about fish.
This latest health scare has had a big impact on the industry and people's diets. We ask if there is really anything to worry about.
The programme also looks at how health scares happen, whether you can believe the tabloid press, and what you need to know to make decisions about your health.
Our presenter, Richard Hammond, tries to get some explanations from the tabloid editors and health correspondents who write the headlines. He also meets a statistician to help put the risks into context.
Richard starts by meeting Dr David Carpenter, a member of a team of researchers that published a study of the quality of farmed salmon in the journal Science. The study found significant levels of harmful chemicals in some samples.
News reports, quoting a line from the study that said farmed salmon is only safe to eat three times a year, started a health scare.
Carpenter's research focused on the levels of dioxins and PCBs in farmed salmon. These are man-made chemicals that build up in our bodies and can, in large doses, lead to cancer.
Carpenter's study of salmon around the world concludes that salmon farmed in Northern Europe is particularly high in man-made contaminants. So Richard invites him to fly to Scotland to visit the salmon farms of Orkney and talk to those affected by the scare.
Carpenter visits a farm that had to lay off staff after the news reports about contaminated salmon. There he discusses the fish's food - which is believed to be the source of the PCBs and dioxins - and sees how alternatives are being found that lower the levels in the salmon.
Is farmed salmon safe?
There are several unanswered questions:
- Does farmed salmon have higher contaminant levels than other foods?
- How much farmed salmon is safe to eat?
We tested semi-skimmed milk, minced beef and eggs, as a snapshot of what is in our food. Farmed salmon actually contained lower levels of PCBs and dioxin than the mince and eggs. Our test, while only on a small sample, shows that these chemicals can exist in other foods, not just farmed salmon.
The World Health Organization, the UK Food Standards Agency and the US Food and Drug Administration offer different advice about what is safe. Because the harmful chemicals are stored in our fatty tissues and build up over time, there is some disagreement about how much salmon is advisable to eat.
The Food Standards Agency points out that there is good evidence that eating oily fish like salmon reduces the risk of heart disease. Their website has the latest advice about what amount of farmed salmon is safe to eat and other nutrition advice.
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