In my previous article, "Mercury in Seafood,"1 I told the story of a patient who was advised to avoid salmon because it was high in mercury. As we know, mercury bioaccumulation in salmon is not a problem. Unfortunately, salmon - specifically farmed salmon - can be high in other toxins, such as polychlorinated biphenyls and dioxins.Over time, these can increase in the body to levels such that the risk of death from cancer is increased.
This brings us to a common occurrence regarding nutrition. Specifically, nutritional research is so dynamic the public gets confused. In my two decades of practice, patients have been told:
- protein is bad;
- fat is bad;
- carbohydrates are good;
- protein is good;
- fat is good;
- carbohydrates are bad;
- there are good carbohydrates and bad carbohydrates; and
- there are good fats and bad fats.
The story of good fats and bad fats began when Dr. Nathan Pritikin challenged conventional wisdom with a radical theory that fats were unhealthy and could increase the risk of death, especially from heart disease. As researchers began to test Dr. Pritikin's theory, it became clear that he had identified an area of nutrition that had essentially been overlooked. Dr. Pritikin's theories on high fat consumption were generally validated until the Eskimos were studied. Of course, what was then the Eskimo paradox became the basis for the good fat/bad fat recommendations of today. In reality, there are no bad fats. They become bad when the amount we eat reaches a level that causes more problems than solutions. Or a good fat is good until/unless we over consume it. The good fat/bad fat research showed that the typical Western diet (especially the typical American diet) was lacking in fats from the omega-3 family and was too high in omega-6 and saturated fat. One of the tastiest and most plentiful sources of omega-3 fatty acids comes from salmon. (For a complete list of the amounts of omega-3 fatty acids in seafood, please see the chart in my article "Omega-3 Fatty Acids in Seafood."2)
A few years ago, the "what was good for you is now bad" virus attacked salmon when it was discovered there were high levels of PCBs and dioxins in farmed salmon. Salmon farming began in response to increased demand by health-conscious consumers. Since omega-3 fatty acids were a key selling point, farmers fed salmon fish that would yield maximum amounts. They did not realize the fish that raised omega-3 yields also contained PCBs.
Polychlorinated Biphenyls (PCBs)
PCBs are chemicals that have been banned in the United States for 30 years. Although this has resulted in decreased levels overall, PCBs break down very slowly and thus continue to be present in the environment. PCBs were generated from the production of pesticides, inks, paints and fire-resistant materials. PCBs are part of a group of 12 chemicals called persistent organic pollutants. Like mercury, the PCB content in fish can vary widely depending on the species, geographical location and types of food the fish have consumed.
Mozaffarian and Rimm3 sited seven studies of PCBs in farmed salmon. In parts per billion, the PCB content for each of the seven studies was as follows: 15, 21, 25, 26, 38, 40, and 51 ppb, respectively. In three wild-salmon studies, the levels were 0.5, 3.0, and 5.0. One of the above studies was the USDA Total Diet Study4 which showed the average PCB content of farmed salmon as 26. In that same study, it was revealed that the PCB levels averaged 18 in pork, 22 in beef, 32 in chicken and 70 in butter. The FDA action level is 2,000 ppb of PCBs.
Dioxins (Dibenzodioxides and Dibenzofurans)
These chemicals come from burning garbage, the manufacture of pesticides, polyvinyl chloride plastics and paper bleaching. Dioxin emissions have been cut 90 percent in the last 20 years according to the U.S. Environmental Protection Agency. Unfortunately, they also persist in the environment for a long time and continue to be present in the food chain.
Risk of Mortality
By now, your patients and mine are pulling their hair out. I have heard patients say, "So, if I eat the salmon, I die of cancer. If I don't eat the salmon, I die of heart disease. Is that correct?" I answer in the affirmative - with an explanation. Recently, a quantitative risk-benefit analysis was completed. Its premise was how the consumption of salmon at a level to provide 1,000 mg of EPA and DHA daily over a 70-year lifespan would affect mortality.5 They concluded that (per 100,000 individuals), consumption of farmed salmon over a lifetime would triple the death rate from cancer from eight out of 100,000 to 24 out of 100,000. They also calculated that the consumption of salmon at this rate over a lifetime (when compared to the current standard American diet) would result in more than 7,100 fewer deaths from coronary heart disease.
In the FDA study cited above,4 other notable seafood sources of PCBs included sardines, which were tested at 57 ppb; light skipjack tuna, 45 ppb; and white albacore tuna, 100 ppb. As of this date, the available data on PCB levels in fish is much less extensive than it is for mercury. Regarding dioxins, the fish with potentially high levels included farmed catfish, halibut, Atlantic herring, Atlantic mackerel, sardines, trout, crab, lobster and oysters. Currently, it's difficult to determine how much is too much, since there is not yet an FDA action level.
To put this in perspective, based on what we currently know, foods high in the so-called bad fats (like cheeseburgers, fries and shakes) have a greater potential to cause long-term problems than seafood containing industrial toxins.
- Andersen GD. "Mercury in Seafood." Dynamic Chiropractic, July 30, 2007. www.chiroweb.com/archives/25/16/02.html.
- Andersen GD. "Omega-3 Fatty Acids in Seafood." Dynamic Chiropractic, 2007. www.chiroweb.com/archives/25/14/02.html.
- Mozaffarian D, Rimm EB. Fish Intake, Contaminants and Human Health: Evaluating the Risks and Benefits. JAMA, 2006;296(15):1885-99.
- USFDA. Food Drug Administration Total Diet Study. Available at: http://vm.cfsan.fda.gov/-comm/tds-toc.html/tds-toc.html.
- Foran JA, Good DH, Carpenter DO, et al. Quantitative analysis of the benefits and risks of consuming farmed and wild salmon. J Nutr, 2005;135:2639-43.
Click here for previous articles by G. Douglas Andersen, DC, DACBSP, CCN.