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The secret story of fish: decreasing nutritional value due to pollution?

Published online by Cambridge University Press:  24 May 2012

Jérôme Ruzzin
Department of Biology, University of Bergen, Bergen5020, Norway, email
David R. Jacobs Jr
Division of Epidemiology, School of Public Health, University of Minnesota, Minneapolis, MN55454, USA Department of Nutrition, School of Medicine, University of Oslo, Oslo, Norway
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Invited Commentary
Copyright © The Authors 2012

Fish, especially fatty fish, have long been viewed as a healthy dietary component because of their unique content of long-chain n-3 PUFA (n-3 fatty acids). An observation in 852 male residents of Zutphen, The Netherlands, aged 40–59 years in 1960 indicated that fish intake was inversely associated with the incidence of CHD over 20 years of follow-up(Reference Kromhout, Bosschieter and de Lezenne Coulander1). On the other hand, fish may also contain diverse environmental pollutants such as heavy metals and persistent organic pollutants (POP), including organochlorine pesticides, polychlorinated biphenyls (PCB), dioxins, polybrominated diphenylether (PBDE) and perfluorinated compounds (PFCO). Therefore, different studies evaluating potential risks v. benefits of fish consumption, especially with respect to CVD, have been performed. Although various results have been reported(Reference Hooper, Thompson and Harrison2), it has generally been suggested that the benefits of fish eating outweigh the risks(Reference Mozaffarian and Rimm3). Compared with CVD, the situation for diabetes has remained largely unexplored. Recently, several prospective studies have documented that the consumption of fish was associated with a higher later occurrence of type 2 diabetes(Reference Djousse, Gaziano and Buring4Reference van Woudenbergh, van Ballegooijen and Kuijsten6), a disease strongly linked to heart disease and stroke, yet that has a much distinct pathophysiology linked to glucose dysregulation and microvascular deterioration. In this issue of the British Journal of Nutrition, a meta-analysis performed by Zhou et al. (Reference Zhou, Tian and Jia7) summarises these(Reference Djousse, Gaziano and Buring4Reference van Woudenbergh, van Ballegooijen and Kuijsten6) and other studies, concluding that fish and n-3 fatty acid consumption is associated with a significantly increased risk of type 2 diabetes. In two other meta-analyses of the same topic and of largely the same data, it has been concluded that there was no benefit from fish intake in terms of reduced diabetes risk(Reference Wallin, Di Giuseppe and Orsini8, Reference Xun and He9). How can we explain these findings? Have the health effects associated with fish consumption been overestimated?

At an experimental level, several pieces of evidence support the idea that the health effects of fish consumption vary depending on the presence or absence of POP. Rats exposed to contaminated salmon oil (containing background levels of POP) developed metabolic complications linked to type 2 diabetes, whereas animals exposed to decontaminated salmon oil (treated to achieve very low levels of POP) did not show such disturbances(Reference Ruzzin, Petersen and Meugnier10). Furthermore, mice fed commercially available farmed salmon fillet with common POP levels were found to develop insulin resistance, glucose intolerance, visceral obesity, fatty liver and chronic low-grade inflammation, in contrast to mice fed farmed salmon fillet containing lower levels of POP, which showed a better metabolic profile(Reference Ibrahim, Fjaere and Lock11). In addition, consumption of salmon protein hydrolysate containing less than 0·2 % of lipids, and therefore very low concentrations of POP, was found to protect rats against insulin resistance induced by a high-fat diet containing lard and ‘corn oil’(Reference Ruzzin, Turcotte and Leblanc12). Taken together, these findings emphasise that background levels of POP, which many people consider to be at safe levels, can completely counteract the potential benefits of n-3 fatty acids and other nutrients present in fish, in particular leading to the serious metabolic features which often precede type 2 diabetes. Thus, these animal feeding studies are consistent with the recent human prospective and cross-sectional studies showing an association between type 2 diabetes and POP(Reference Lee, Steffes and Sjodin13Reference Airaksinen, Rantakokko and Eriksson15).

Previously, Kaushik et al. (Reference Kaushik, Mozaffarian and Spiegelman5) reported that, whereas fish and n-3 fatty acid intake increases the risk of diabetes, the consumption of n-3 fatty acid supplements did not. Interestingly, the oil found in most n-3 fatty acid supplements differs considerably from the oil found in fatty fish, in that most lipophilic pollutants such as POP have been extracted through decontamination processes. On the other hand, the oil present in fatty fish has not been decontaminated, and often contains many POP because these pollutants are omnipresent in aquatic environments, making fatty fish one of the most important sources of human exposure to POP(Reference Schecter, Colacino and Haffner16). Furthermore, the presence of POP in fish, compared with other food products, is still poorly regulated(Reference Ruzzin17). In the European Union, the levels of organochlorine pesticides, PCB and PBDE in fish and seafood are, for instance, still unregulated. Thus, the exposure to POP through fatty fish intake could have contributed to an enhanced risk of diabetes. These findings also pinpoint that the common practice to extrapolate the results obtained with n-3-derived supplements to fatty fish, or seafood in general, has probably led to a serious misinterpretation and should be done with extreme caution.

The concentrations and types of POP mixtures may vary substantially in fatty fish depending on the food consumed, the time and the geographic area of the fish(Reference Hites, Foran and Carpenter18, Reference Arkoosh, Strickland and Van Gaest19). Similarly, although n-3-derived supplements may contain lower levels of POP than fatty fish, the levels of POP in these supplements may fluctuate considerably due to differing methods used by the industry to refine the oil, including activated carbon adsorption, short-path distillation and deodorisation(Reference Bourdon, Bazinet and Arnason20Reference Fernandes, Rose and White22). This varying quality of fish and n-3-derived supplements has probably contributed to the different findings about the health effects of seafood. In addition, fish oil supplements do not contain the food matrix of the whole fish.

Environmental pollutants present in fish are not the only factors that can affect the health outcomes associated with fish intake. More than half of the total fish for human consumption is provided by aquaculture. Because of the limited natural resource and expensive prices, marine oils used in aquafeeds are often replaced by vegetable oils(Reference Naylor, Hardy and Bureau23). As a consequence, fish currently sold in supermarkets are, from a nutritional perspective, considerably different from the fish that were available some years ago. Between 2005 and 2009, the ratio of EPA (20 : 5n-3) and DHA (22 : 6n-3) to n-6 PUFA has, for instance, decreased by about 50 % in farmed Atlantic salmon(24), one of the most consumed fishes worldwide. Thus, to the extent that the particular oils supplied by fish are important in human metabolism, the potential benefits of fish have probably changed throughout the years and decades because fish per se has been under continuous nutritional adaptations. In line with this, Kromhout et al. (Reference Kromhout, Yasuda and Geleijnse25) recently pointed out that the strongest reductions in cardiovascular endpoints associated with the consumption of n-3 fatty acids were obtained in the oldest human trials, whereas recent studies did not found such positive effect. There have also been studies reporting that plasma n-3 fatty acid concentrations are relatively similar between fish eaters and non-fish eaters(Reference Welch, Shakya-Shrestha and Lentjes26, Reference Pawlosky, Hibbeln and Lin27), thereby challenging the idea that fatty fish intake is essential for the supply of n-3 fatty acids, at least in populations that do not eat large amounts of fish. It is interesting in this line of thought that both Wallin et al. (Reference Wallin, Di Giuseppe and Orsini8) and Xun & He(Reference Xun and He9) found inverse relationships of fish intake with diabetes in several studies in China, Japan and Australia. Among other explanations of this geographic interaction, the finding in Asian countries could be indicative of differential distribution of POP by geographic area. We note that this geographic interaction is somewhat sensitive to the specific analysis model, since inverse associations strengthened on re-analysis of the original data by Xun & He(Reference Xun and He9).

The emerging evidence(Reference Zhou, Tian and Jia7Reference Xun and He9) suggests that n-3 fatty acid and fatty fish intake has no significant benefits on type 2 diabetes, while recent studies find little benefit for CVD, as well(Reference Kromhout, Yasuda and Geleijnse25). This discouraging state of affairs has probably emerged through human intervention in the lives of the fish, both through exposure to a wide variety of chemical contaminants and through substantial alteration in fish composition as fish source has moved from fish caught in the wild to fish farmed for financial profit. These studies may be taken as a warning for the need to maintain stewardship of the land and the sea, as we strive for adequate quality of life in an increasingly populous earth.


1Kromhout, D, Bosschieter, EB & de Lezenne Coulander, C (1985) The inverse relation between fish consumption and 20-year mortality from coronary heart disease. N Engl J Med 312, 12051209.CrossRefGoogle ScholarPubMed
2Hooper, L, Thompson, RL, Harrison, RA, et al. (2006) Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review. BMJ 332, 752760.CrossRefGoogle ScholarPubMed
3Mozaffarian, D & Rimm, EB (2006) Fish intake, contaminants, and human health – evaluating the risks and the benefits. JAMA 296, 18851899.CrossRefGoogle ScholarPubMed
4Djousse, L, Gaziano, JM, Buring, JE, et al. (2011) Dietary omega-3 fatty acids and fish consumption and risk of type 2 diabetes. Am J Clin Nutr 93, 143150.CrossRefGoogle ScholarPubMed
5Kaushik, M, Mozaffarian, D, Spiegelman, D, et al. (2009) Long-chain omega-3 fatty acids, fish intake, and the risk of type 2 diabetes mellitus. Am J Clin Nutr 90, 613620.CrossRefGoogle ScholarPubMed
6van Woudenbergh, GJ, van Ballegooijen, AJ, Kuijsten, A, et al. (2009) Eating fish and risk of type 2 diabetes: a population-based, prospective follow-up study. Diabetes Care 32, 20212026.CrossRefGoogle ScholarPubMed
7Zhou, Y, Tian, C & Jia, C (2012) Association of fish and n-3 fatty acid intakes with the risk of type 2 diabetes: a meta-analysis of prospective studies. Br J Nutr 108, 408417.CrossRefGoogle Scholar
8Wallin, A, Di Giuseppe, D, Orsini, N, et al. (2012) Fish consumption, dietary long-chain n-3 fatty acids, and risk of type 2 diabetes: systematic review and meta-analysis of prospective studies. Diabetes Care 35, 918929.CrossRefGoogle ScholarPubMed
9Xun, P & He, K (2012) Fish consumption and incidence of diabetes: meta-analysis of data from 438,000 individuals in 12 independent prospective cohorts with an average 11-year follow-up. Diabetes Care 35, 930938.CrossRefGoogle ScholarPubMed
10Ruzzin, J, Petersen, R, Meugnier, E, et al. (2010) Persistent organic pollutant exposure leads to insulin resistance syndrome. Environ Health Perspect 118, 465471.CrossRefGoogle ScholarPubMed
11Ibrahim, MM, Fjaere, E, Lock, EJ, et al. (2011) Chronic consumption of farmed salmon containing persistent organic pollutants causes insulin resistance and obesity in mice. Plos One 6, e25170.CrossRefGoogle ScholarPubMed
12Ruzzin, J, Turcotte, S, Leblanc, V, et al. (2007) Dietary salmon protein improves insulin sensitivity in high-fat fed obese rats. Ann Nutr Metab 51, 347.Google Scholar
13Lee, DH, Steffes, MW, Sjodin, A, et al. (2010) Low dose of some persistent organic pollutants predicts type 2 diabetes: a nested case–control study. Environ Health Perspect 118, 12351242.CrossRefGoogle ScholarPubMed
14Lee, DH, Lind, M, Jacobs, DR Jr, et al. (2011) Polychlorinated biphenyls and organochlorine pesticides in plasma predict development of type 2 diabetes in the elderly: The Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. Diabetes Care 34, 17.CrossRefGoogle ScholarPubMed
15Airaksinen, R, Rantakokko, P, Eriksson, JG, et al. (2011) Association between type 2 diabetes and exposure to persistent organic pollutants. Diabetes Care 34, 19721979.CrossRefGoogle ScholarPubMed
16Schecter, A, Colacino, J, Haffner, D, et al. (2010) Perfluorinated compounds, polychlorinated biphenyls, and organochlorine pesticide contamination in composite food samples from Dallas, Texas, USA. Environ Health Perspect 118, 796802.CrossRefGoogle ScholarPubMed
17Ruzzin, J (2012) Public health concern behind the exposure to persistent organic pollutants and the risk of metabolic diseases. BMC Public Health 12, 298.CrossRefGoogle ScholarPubMed
18Hites, RA, Foran, JA, Carpenter, DO, et al. (2004) Global assessment of organic contaminants in farmed salmon. Science 303, 226229.CrossRefGoogle ScholarPubMed
19Arkoosh, MR, Strickland, S, Van Gaest, A, et al. (2011) Trends in organic pollutants and lipids in juvenile Snake River spring Chinook salmon with different outmigrating histories through the Lower Snake and Middle Columbia Rivers. Sci Total Environ 409, 50865100.CrossRefGoogle ScholarPubMed
20Bourdon, JA, Bazinet, TM, Arnason, TT, et al. (2010) Polychlorinated biphenyls (PCBs) contamination and aryl hydrocarbon receptor (AhR) agonist activity of omega-3 polyunsaturated fatty acid supplements: implications for daily intake of dioxins and PCBs. Food Chem Toxicol 48, 30933097.CrossRefGoogle ScholarPubMed
21Marti, M, Ortiz, X, Gasser, M, et al. (2010) Persistent organic pollutants (PCDD/Fs, dioxin-like PCBs, marker PCBs, and PBDEs) in health supplements on the Spanish market. Chemosphere 78, 12561262.CrossRefGoogle ScholarPubMed
22Fernandes, AR, Rose, M, White, S, et al. (2006) Dioxins and polychlorinated biphenyls (PCBs) in fish oil dietary supplements: occurrence and human exposure in the UK. Food Addit Contam 23, 939947.CrossRefGoogle ScholarPubMed
23Naylor, RL, Hardy, RW, Bureau, DP, et al. (2009) Feeding aquaculture in an era of finite resources. PNAS 106, 1510315110.CrossRefGoogle Scholar
24National Institute of Nutrition and Seafood Research (2011) = 168 (accessed 29 July 2011).Google Scholar
25Kromhout, D, Yasuda, S, Geleijnse, JM, et al. (2011) Fish oil and omega-3 fatty acids in cardiovascular disease: do they really work? Eur Heart J 33, 436443.CrossRefGoogle ScholarPubMed
26Welch, AA, Shakya-Shrestha, S, Lentjes, MA, et al. (2010) Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the product-precursor ratio [corrected] of alpha-linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort. Am J Clin Nutr 92, 10401051.CrossRefGoogle Scholar
27Pawlosky, RJ, Hibbeln, JR, Lin, Y, et al. (2003) Effects of beef- and fish-based diets on the kinetics of n-3 fatty acid metabolism in human subjects. Am J Clin Nutr 77, 565572.CrossRefGoogle ScholarPubMed
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