As previously documented, a diet that balances omega-3 and omega-6 consumption seems to be optimal for human health. Today, omega-6 fats are prevalent in our diets because they are in many foods containing seed oils, such as corn and canola oil. To balance the ratio of omega-3 to omega-6, many researchers have encouraged reducing seed oil consumption and increasing fish consumption. Wild salmon is a great source of omega-3 fatty acids and farmed salmon usually has an even higher omega-3 fatty acid content. However, salmon is also has high levels of dioxin, a carcinogen and endocrine disrupter. So, should salmon be included as a part of a healthy diet or avoided because of toxicity concerns?
I began researching salmon because I was curious about whether farmed salmon had as favorable a lipid content as wild salmon. I found two papers (1,2) that compared the fatty acid content of wild versus farmed salmon. The farmed salmon measured up well. It had a higher level of omega-3 fatty acids than wild salmon. Farmed salmon also had a higher level of omega-6 fatty acids. The ratio of omega-3 to omega-6 was slightly lower in the farmed salmon. However, I concluded that farmed salmon provided a very healthy fat profile and was roughly equivalent to wild salmon.
But in the studies, I found concerns about the dioxin content of fatty fish. Dioxins are a group of chemicals released as industrial pollution. In addition to being a potent carcinogen, dioxin also acts as an endocrine disrupter, meaning that consumption of dioxin may cause feminizing effects, especially in children. There have been a multitude of studies in animals and humans showing negative effects of dioxin.
Dioxins collect in fat and levels vary between foods. Dioxin levels are measured in units termed “total dioxin-like toxic equivalency” (TEQ). Figure 1 shows a comparison of dioxin concentrations of wild and farmed salmon from several regions and other foods. In general, European farmed salmon has higher levels of dioxins than American farmed salmon.
Figure 1. Dioxin Concentration of Salmon and Other Foods. WS= Wild Salmon; FS=Farmed Salmon. Levels of dioxin were much higher in farmed than wild salmon. Wild salmon dioxin concentrations varied depending on type of salmon. The wild salmon from SE Alaska (Chinook) had the highest levels of dioxin, while others (Coho, Pink, Chum) from the same area had similar levels as Kodiak and BC wild salmon. Butter has a high level of dioxin per gram but dioxin intake from butter would be lower when accounting for serving size. Sources: (1,2).
At present there are no federal guidelines for salmon consumption with respect to dioxin. A 2005 report in Environmental Health Prospectives found that to meet the U.S. EPA’s recommendation for dioxin consumption, farmed salmon would need to be eliminated entirely from the diet and wild salmon would need to be limited to once per month to minimize cancer risks. This may be overly cautious. The European equivalent would allow for one farmed salmon meal per month or 16 wild salmon meals per month. It is important to note that these estimates do not account for dioxin intake from non-salmon sources.
Unfortunately, industrial pollution has turned salmon, a once very healthy food source, into a potential health hazard. It is difficult to weigh the benefits of the omega-3 content of salmon against the negative of toxicity issues. One thing to keep in mind is that dioxins stay in the body for a very long time. They have a half-life of 7 to 11 years. So even if a small amount of dioxin is ingested at a meal, the cumulative effect over the course of a lifetime can be great. For that reason, I suggest that people limit salmon consumption and definitely choose wild rather than farmed salmon. Please note that nearly all Atlantic salmon is farmed. Pacific salmon is generally wild caught but can also be farmed. To my knowledge, there are no labeling requirements to distinguish wild versus farmed salmon. If the package does not clearly indicate the salmon is wild-caught, it is most likely farmed.
Fortunately, fish oil supplements are usually free of dioxins because they are produced from fish that are lower on the food chain and any contaminants are removed. The one dietary supplement I recommend is fish oil because of its wide ranging health benefits and the limited availability of safe food sources of omega-3 fatty acids. Be sure to buy fish oil from a reputable company that tests the levels of dioxins.