Farmed Vs Wild Salmon
The problems with farmed fish: the example of salmon
Farmed fish remain a sustainable, popular and affordable option for eating out. Salmon is an excellent choice for taking in healthy omega 3 fatty acids and vitamin D, both of which carry tremendous health benefits. The reality however is that farmed salmon, and potentially other farmed fish, can be quite unhealthy, due to the presence of accumulated pollutants or improper (but popular) feeding practices that change the nutritional properties of the fishes.
Persistent Organic Pollutants
Due to improper disposal of industrial waste, certain organic pollutants have contaminated the global ecosystem. Good examples are the cancer-causing polychlorinated biphenyls (PCBs) and the endocrine disrupting insecticide DDT, which are non-degradable, fat-soluble toxic compounds accumulating to fatty tissues. Salmon is an oily fish, and therefore its tissues are naturally rich in presumably healthy oils, which make it susceptible to accumulating fat soluble toxins, such as PCBs and DDT, throughout its lifetime. Since these toxins are non-degradable, this toxic load cannot be metabolised or eliminated in any way; it will just get transferred to the next link in the food chain: us.
As a carnivorous fish, wild salmon preys on krill and shellfish, both of which are very rich sources of marine oils, which is why salmon is so rich in healthy omega 3 oils. But commercially farmed salmon cannot be raised on krill and shellfish, if production is going to be kept at a reasonable cost, both for farmers and consumers. The natural diet is therefore substituted by a meal produced by a variety of other wild fish and marine organisms.
The amount of toxins found in salmon (or any other animal) depends on how contaminated its food source is. Therefore, depending on the origin of the wild fish and how long they had been exposed to toxins, a certain toxic load will be inevitably transferred to salmons. Obviously, this problem exists both for farmed and wild salmons, but it is surprisingly more pronounced in farmed salmons.
According to a study published in the journal “Science” in 2004, farmed salmon had up to 8 times higher levels of PCBs compared to wild salmon. This finding raises many questions regarding the origins and quality of the wild fish used for feeding the salmons.
Farmed salmon had up to 8 times higher levels of PCBs compared to wild salmon.
PCBs have been shown in the lab to cause cancer (especially non-Hodgkin’s lymphoma), neurological disorders and can also act as endocrine disruptors. Long-term PCBs and DDT poisoning has also been shown to cause diabetes and obesity.
Vegetable oils
The natural diet of salmon (shellfish and krill), provides the pigments that give its flesh the characteristic bright orange — almost red colour (not to be confused with the pinkinsh colour of farmed salmon that is achieved by adding carotenoids astaxanthin and canthaxanthin in the feed). As explained above, the usual diet of farmed salmons (meal made of wild fish) covers the needs of salmons for oils and protein, but has two major drawbacks. First, it is confirmed that it results in high levels of environmental toxins and secondly it is quite expensive. Therefore, salmon farmers looked for a more affordable way to provide salmons the oils they need.
Vegetable oils (canola oil, soybean oil etc) were originally selected as a more affordable and less contaminated substitute of the marine fats (fish oils). While this feeding practice partially alleviated the contamination with PCBs and DDT, the new problem is that these oils significantly reduce the beneficial omega 3 oils present in salmon tissues and increase the amount of inflammatory omega 6 fatty acids, such as linoleic acid. A study published in 2013 in the journal “PLOS One” found that salmons fed with vegetable oils developed insulin resistance and accumulated fat in the liver. On the other hand, salmon fed with natural fish oils did not cause these problems.
Apart from the insulin resistance and fatty liver, another study published in 2013 in the “British Journal of Nutrition” found that eating salmons fed with soybean oil actually causes obesity and inflammation. This is not a surprise of course since the omega 6 fatty acids (linoleic acid) and metabolites which dominate the salmon tissues, are highly inflammatory and have been associated with a variety of inflammatory conditions. The authors of the above study reported that feeding salmons with soybean oil, increased the tissue content of omega 6 fatty acids by 530%. At the same time the content of beneficial omega 3 oils, such as DHA and EPA was reduced by 56% and 71% respectively. It is exactly this combination of inferior amounts of omega 3s with increased amounts of inflammatory omega 6s that seems to cause obesity and diabetes.
It is important to mention that soybean oil (a major source of linoleic acid) is the oil of choice in experiments, when scientists want to force guinea pigs to get fat and study them. This is true for humans as well, because according to a study published in the journal “Obesity” in 2012, dietary linoleic acid causes obesity. The only way to counteract the harmful effects of linoleic acid and omega 6 fatty acids in general is the increase in omega 3 fatty acids, such as DHA and EPA. Needless to say that soybean oil is one of the most popular cooking oils with 43.6 million metric tons used worldwide in 2012–13, according to the Statistics Portal. At the same time, obesity and diabetes have become modern epidemics with more than 35% of American adults (and 17% of children) being obese and more than 8% being diabetic (that is almost 26 million people), with figures expected to increase significantly in the next decades.
References
- Ronald A. Hites R.A. et al. 2004. Global Assessment of Organic Contaminants in Farmed Salmon. Vol. 303 no. 5655 pp. 226–229
http://www.sciencemag.org/content/303/5655/226.abstract - Lisa Kolden Midtbø et al., 2013. Intake of Farmed Atlantic Salmon Fed Soybean Oil Increases Insulin Resistance and Hepatic Lipid Accumulation in Mice. PLOS One.
http://www.ncbi.nlm.nih.gov/pubmed/23301026 - Alvheim A. et al. 2013. Dietary linoleic acid elevates endogenous 2-arachidonoylglycerol and anandamide in Atlantic salmon (Salmo salar L.) and mice, and induces weight gain and inflammation in mice. Br J Nutr. 109(8): 1508–1517.
http://www.ncbi.nlm.nih.gov/pubmed/22883314 - Alvheim AR, et al. 2012. Dietary linoleic acid elevates endogenous 2-AG and anandamide and induces obesity. Obesity (Silver Spring). 20(10):1984–94.
http://www.ncbi.nlm.nih.gov/pubmed/22334255
In collaboration with Eleni Roumeliotou, a clinical nutritionist, geneticist and founder of Primal Baby.
