Fish contains many important nutrients, but can, as for other food, contain undesirable substances.

The Norwegian authorities recommend that we eat 300-450 grams of fish a week. Half of this should be fat fish.

Depending on whether you eat lean or fat fish, there are different nutrients and undesirable substances that you should be aware of. In recent years, the undesirable substances that have sparked most debate have been heavy metals and organic environmental toxins. If you divide seafood into fat and lean species, you will find most of the organic environmental toxins in the muscle tissue of fat fish and in the liver of lean fish. These compounds are also found in a number of other types of food. The content of heavy metals in the different species is less affected by whether the species is regarded fat or lean.

How much fish is it safe to eat?

For most substances, it is the quantity we consume that determines whether the substance is toxic or not. This applies both to nutrients and undesirable substances.

Expert groups from the World Health Organization (WHO), among others, have therefore stipulated how much of certain undesirable substances we tolerate in our food without it posing any risk to our health. These values are called tolerable weekly intake (link).

Dioxins and dioxin-like PCBs are one of the environmental toxins for which a tolerable weekly intake has been stipulated, namely 14 pg/kg bodyweight per week. This means that a person weighing 70 kg can tolerate 980 pg per week throughout their life without any risk to their health. Given the current levels in herring, mackerel and farmed salmon, we can eat fat fish for dinner almost every day without exceeding this quantity. This is also bearing in mind the intake from other food such as eggs, milk and meat.

More dangerous not to eat fish

The WHO and the Food and Agriculture Organization of the United Nations (FAO), have created a model in which they have weighed the favourable effects of eating seafood against the potential negative health effects. They have concluded that not eating seafood is considerably more dangerous. Firstly, they have weighed the importance of marine omega-3 for protection against cardiovascular disease against the risk of cancer from dioxins and dioxin-like PCBs. The risk of cancer in this context is negligible compared with the protection against cardiovascular disease.

Secondly, they have weighed the importance of marine omega-3 for foetal brain development against the risk of intereference with brain development because of methylmercury. The conclusion from this model is that pregnant women should increase their seafood intake because it improves the child’s verbal skills.

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