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Heavy metals -

The main concern when it comes to consuming fish is the presence of heavy metals and other pollutants. A particular area of concern is polychlorinated biphenyls (PCBs).

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PCBs -

PCBs were banned during the 1980s because of their harmful effects on human health, but prior to being banned they were used widely in electrical apparatus.

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PCBs -

Considerable quantities of PCBs still linger in our soil and water and although they are found in many foods and even drinking water, their concentration is usually highest in fish.

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PCBs -

The proven negative health effects of PCBs are numerous and they have been shown to impact everything from the immune system to the brain.

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Pregnancy -

For this reason the NHS recommends that pregnant and breastfeeding women limit their consumption of fish most likely to contain high levels of PCBs and other pollutants such as dioxins.

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Pregnancy -

These include oily fish such as salmon and sardines, as well as non-oily fish such as crab and sea bass. The recommended portion size is around 140 grams.

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Mercury -

Another worry is the presence of mercury, which has been proven dangerous to developing fetuses and linked with diseases such as cancer and diabetes.

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Mercury -

Again, mercury can be found in a number of foods, but its occurrence in fish is thought to be especially high. One study found that 78% of participants’ intake came from fish and seafood.

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Pregnancy -

Due to the presence of mercury, the US Food and Drug Administration recommends that pregnant women consume only one portion per week of certain fish, including halibut and tuna.

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Over-exaggeration? -

However, Jonathan Napier of Rothamsted Research, Hertfordshire, says that concerns about the presence of heavy metals in fish have been over-exaggerated.

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Over-exaggeration? -

For Napier, the metal content in fish is only a problem for fish that live a particularly long time, such as swordfish. Otherwise, the benefits of eating fish (omega-3) outweigh the risks.

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Omega-3 -

A widely recognized benefit of eating oily fish, such as salmon and tuna, is a reduced risk of cardiovascular disease. This is due to the presence of omega-3 fatty acids EPA and DHA.

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EPA and DHA -

Both EPA and DHA have been shown to reduce inflammation in the body, thereby reducing the risk of illnesses such as heart disease, cancer, and diabetes.

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Fish supplements -

Fish supplements may provide a risk-free omega-3 source. However, a study by the World Health Organization (WHO) suggests supplements don't have the same benefits as eating oily fish.

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Plant-based omega-3 sources -

There are also plant-based sources of omega-3s and a 2014 study suggested that these may have health benefits similar to oily fish. There is no substantial research to support this yet, however.

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Declining levels of omega-3 -

Overall it seems that eating oily fish is important for getting omega-3s. It should be noted, however, that research shows the levels of omega-3s in the fish we eat are declining.

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Brain food -

Eating fish has long been associated with having a healthy brain. Indeed, studies have linked the consumption of omega-3s with slower cognitive decline.

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Brain volume -

Independently of this, a recent study has also linked eating baked or broiled fish with having a larger brain volume, which is in turn indicative of better health.

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Inflammatory effect -

According to Cyrus Raji, assistant professor of radiology and neurology at Washington University, the connection may be because of the anti-inflammatory effect of fish.

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Start early -

Raji recommends starting to eat fish at least once a week in your twenties or thirties in order to make your brain as resistant as possible to dementia.

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Uncertain conclusions -

Although most scientists agree that the omega-3 content of oily fish makes it beneficial to human health, it is difficult to draw a conclusion about whether eating fish is healthy or not.

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Study limits -

Indeed, it is difficult to conduct population studies, such as the WHO study of the health benefits of fish supplements, that do not produce skewed results.

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Study limits -

Fish is generally a more expensive food and it is widely accepted that socioeconomic status impacts health. It’s therefore possible that higher-income families are generally healthier.

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Study limits -

Although researchers of course try to account for such confounding variables, they may not always catch everything that could cause a skewed result.

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Further complications -

To complicate things further, research suggests that the health benefits from fish may vary from individual to individual, depending on a person’s ability to convert precursor forms of omega-3s.

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Further complications -

It is understood that the ability of a given individual to convert EPA and DHA may come down to diet and lifestyle, but genetics could also play a part.

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Moot question -

Ultimately the question as to how healthy fish really is may soon become redundant, since fish is not a sustainable resource and stocks within biologically sustainable levels are dwindling.

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Algae -

Going forward the focus is more likely to be on how omega-3s can otherwise be obtained. A key focus area is the growing and harvesting of algae.

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Sustainable fishing -

Although fish supplies are in danger, we can all do our part to help maintain them, by making sure we choose the most sustainable fish available.

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Sustainable fishing -

For help with this, the Marine Conservation Society has produced a sustainability guide that lists 133 species of fish and gives them a sustainability rating.

Sources: (BBC) (Marine Conversation Society)

See also: The impact of COVID-19 on the global food chain

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