A walk on the wild side

The debate over which salmon – farmed or wild – is healthier is far from simple.

Question:

Some time ago, Time magazine had an article about the nutritional value of farmed versus wild salmon. The conclusion was that wild salmon was more beneficial to our health. It also discussed the fact that wild salmon have access to naturally occurring nutrients in the food chain. This has caused me to buy only sustainably fished salmon from North America.

Answer:

Wild salmon was heralded as far superior to farmed salmon in Time’s 2015 article “Should I Eat Salmon?” The story quoted experts who said farmed salmon had higher levels of “saturated fat, calories, pollutants and antibiotics”. Since then, however, a Norwegian study published in the journal Environmental Research has suggested this is not always true.

Norwegian researchers collected samples of wild Atlantic salmon, caught in nets in coastal waters by commercial fisherman, and farmed Atlantic salmon, also sourced in Norway.

A standardised fillet of the wild and farmed Atlantic salmon, including its all-important fat, was then analysed for the presence of persistent organic pollutants such as dioxins (polychlorinated dibenzo-p-dioxin and dibenzofuran), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), organochlorine pesticides (OCPs) such as DDT, metals and fatty acids.

Analysis revealed that contaminant levels of dioxins, PCBs, organochlorine pesticides (DDT, dieldrin, lindane, chlordane, mirex and toxaphene) and mercury were higher in the wild salmon – though both types had levels well below the European Union’s maximum recommendations.

Concentrations of selenium, zinc, copper, iron and the omega-3 fatty acid docosahexaenoic acid (DHA) were also higher in the wild salmon.

Levels of cadmium, lead, PBDEs, and the OCPs endosulfan, pentachlorobenzene and hexachlorobenzene were low, and comparable in both wild and farmed fish. There was also no significant difference in the concentrations of the omega-3 fatty acid eicosapentaenoic acid (EPA).

Overall, there was significantly more total fat in farmed than wild salmon, because of a higher

content of both saturated and monounsaturated fatty acids, as well as omega-6 fatty acids, which meant it had a higher omega-6 to omega-3 fatty acid ratio than wild salmon.

So, what does this mean in everyday terms?

Wild Atlantic salmon from off the coast of Norway contained slightly more persistent organic pollutants than farmed salmon. Persistent organic pollutants (POPs) are resistant to degradation and have the potential to affect human health.

However, wild salmon contained less saturated fat (it’s

recommended that our saturated fat intake is limited to less than

10% of our energy intake) and a lower ratio of omega-6 to omega-3 fatty acid. Research suggests a lower ratio is likely to benefit our health, with evidence suggesting it suppresses the development of cardiovascular disease, cancer, and inflammatory and autoimmune diseases.

Although both types of salmon were good sources of omega-3 fats, the more beneficial fatty-acid ratio of the wild salmon potentially makes it a healthier food, even given its slightly higher persistent organic pollutant levels. But either is nutritious.

New Zealand farmed salmon is the Pacific king variety. Unfortunately, we don’t have data on levels of persistent organic pollutants in king salmon, fresh or wild. We know this salmon is a richer source of the desirable omega-3 fatty acids than Atlantic salmon. But it also contains considerably more omega-6 fatty acids.

The last National Nutrition Survey found that nearly 60% of New Zealanders were eating one or fewer servings of fish a week. That’s a shame, because fish is low in saturated fat and an excellent source of protein, omega-3 fatty acids, iodine, selenium and many important vitamins.

So, regardless of whether it’s farmed or wild, fresh or tinned, any fish you add to your weekly diet is likely to be beneficial.

The last National Nutrition Survey found that nearly 60% of Kiwis were eating one or fewer servings of fish a week.