Are Fish Good For You?

Seafood products are well known for their health benefits. For many people across the world fish is an essential source of protein, and the OMEGA-3 fatty acids found in seafood are an important part of maintaining a healthy diet. But for those of us with the luxury of choice, is seafood still the healthiest option? And by looking to reduce our seafood consumption, will we be losing out on vital nutrition?

Seafood products are popular for a variety of reasons. For example, fish such as salmon and tuna are known to be good sources of low-fat protein, whereas cod liver oil is favoured for its high OMEGA-3 fatty acid content. Here we will be looking deeper into the nutritious qualities of fish, using these 3 products as an example.

Salmon

Salmon have very mobile lifestyles, making them a food source with high protein but relatively low fat content [1]. The overfishing of wild salmon populations has made it a common species to be produced by aquaculture – farming the fish in pens along the coast [2]. In recent decades these fish production methods have received a lot of interest as a sustainable alternative to wild salmon, however there are complications involved with aquaculture that could potentially counteract its perceived sustainability [1,3].

Keeping and growing fish in such high densities greatly increases the transfer of parasites and microbes, which can cause catastrophic mass mortalities within fish farms [2-3]. In order to avoid this, farmed fish are treated with a variety of antimicrobial and antibacterial substances, which can lead to the development of resistant bacteria in both fish and the humans that go on to consume them [1-3].

Antibiotics are most commonly administered to farmed fish in their food, as much as 30% of which can be left unconsumed, along with the 80% that are secreted by the fish and deposited into the environment where they can persist for months [1]. Cross-over between marine and terrestrial microbes means that the more widespread these antibiotics and antimicrobials become, the more terrestrial bacteria will also develop resistance and the more complications this will create for human health [1-2].

The aquaculture industry is still expanding and a vast amount of money is being invested in developing solutions to these problems. Yet currently, farmed fish present a risk of both increased disease prevalence and increased antimicrobial resistance.

Tuna

Tuna are one of the most frequently consumed and readily available fish groups globally [4]. Tuna have high metabolisms and therefore high food-intake rates, meaning they accumulate a lot of trace elements over the course of their long life spans [4-5]. Toxins like heavy metals are accumulated and stored in the tissues of the fish, which are then transferred to humans when they consume them [5-6].

The soldering involved in the canning process is another contributing factor to high levels of lead contamination [5]. Research has found that in 8.9% of fresh tuna and 20% of canned tuna, the levels of toxins such as arsenic and lead in tuna products are over the maximum daily intake and legal limits [4-5].

There is research indicating that heavy metal intake can be reduced by eating tuna of a certain size, however as smaller individuals are likely to be younger this may worsen the impact of fishing on the tuna populations themselves [4]. Nevertheless, there is proof that the intake of heavy metals via tuna consumption can be reduced, as long as we have the ability to choose the size of the fish we buy. However, given the position of these species at the top of the food chain, heavy metal accumulation and therefore the intake of these toxins during tuna consumption is unavoidable.

Cod Liver Oil

Cod liver oil is widely used as a nutritional supplement and is well recognised for its supply of Vitamins A, D and essential fatty acids [7]. However, along with these, cod liver oil also contains something called lipid soluble arsenic compounds (arsenolipids) [7-8]. Exposure to inorganic arsenic compounds can have major health implications, including the development of cancer in extreme cases [8]. Once consumed by humans, the arsenolipids found in fish transform into a number of arsenic compounds that could prove toxic or carcinogenic [7].

This research is still insufficient to draw conclusive answers about the toxicity of cod liver oil and this is an area of study that requires more attention, but in the meantime there are alternatives for those requiring nutritional supplementation. As discussed earlier, fish accumulate compounds in their bodies that have been passed up the food chain. Similarly, the high OMEGA-3 fatty acid content of cod is not due to the production of these compounds by the cod themselves but instead due to the consumption of other organisms.

These fatty acid compounds are actually produced by microalgae like plankton, which can accumulate up to 60% of their dry weight in lipids [9]. These microalgal species have been used since the 1960s to produce nutritional supplements as effective as cod liver oil with a fraction of the environmental impact [10]. Algal alternatives to cod liver oil could potentially reduce overfishing, counteract greenhouse gas emissions and make vitamin supplements accessible to vegetarians and vegans at no dietary cost.

What About Consumers?

It is unquestionable that seafood products are an essential source of protein for millions of people around the world. However, for those of us that are fortunate enough to choose how we sustain ourselves, fish may not be the healthiest way to go.

The health benefits marketed to us do not show us the full picture of the foods that we’re eating and in order to maintain a healthy and balanced diet, the facts discussed here should be taken into consideration. These understudied areas of research are further evidence that the information we are given as consumers should always be considered critically as we are very rarely told the whole story.

References

1. Cabello FC, Godfrey HP, Tomova A, Ivanova L, Dölz H, Millanao A, Buschmann AH. Antimicrobial use in aquaculture re‐examined: its relevance to antimicrobial resistance and to animal and human health. Environmental microbiology. 2013 Jul;15(7):1917-42.

2. Sapkota A, Sapkota AR, Kucharski M, Burke J, McKenzie S, Walker P, Lawrence R. Aquaculture practices and potential human health risks: current knowledge and future priorities. Environment international. 2008 Nov 1;34(8):1215-26.

3. Heuer OE, Kruse H, Grave K, Collignon P, Karunasagar I, Angulo FJ. Human health consequences of use of antimicrobial agents in aquaculture. Clinical Infectious Diseases. 2009 Oct 15;49(8):1248-53.

4. Storelli MM, Barone G, Cuttone G, Giungato D, Garofalo R. Occurrence of toxic metals (Hg, Cd and Pb) in fresh and canned tuna: public health implications. Food and chemical toxicology. 2010 Nov 1;48(11):3167-70.

5. Mahalakshmi M, Balakrishnan S, Indira K, Srinivasan M. Characteristic levels of heavy metals in canned tuna fish. Journal of Toxicology and Environmental Health Sciences. 2012 Feb 28;4(2):43-5.

6. Ashraf W. Levels of selected heavy metals in tuna fish. Arabian Journal for Science and Engineering. 2006 Jan 1;31(1A):89.

7. Amayo KO, Raab A, Krupp EM, Feldmann J. Identification of arsenolipids and their degradation products in cod-liver oil. Talanta. 2014 Jan 15;118:217-23.

8. Schmeisser E, Goessler W, Francesconi KA. Human metabolism of arsenolipids present in cod liver. Analytical and bioanalytical chemistry. 2006 May;385(2):367-76.

9. Abd El-Baky HH, El Baz FK, El-Baroty GS. Production of lipids rich in omega 3 fatty acids from the halotolerant alga Dunaliella salina. Biotechnology. 2004;3(1):102-8.

10. Barclay WR, Meager KM, Abril JR. Heterotrophic production of long chain omega-3 fatty acids utilizing algae and algae-like microorganisms. Journal of Applied Phycology. 1994 Apr;6(2):123-9.