The long-chain fatty acids eicosapentanoic acid (EPA, C20:5 (n-3)) and docosahexanoic acid (DHA, C22:6 (n-3)) have been shown to be beneficial to human health. The benefits of EPA and DHA derive from their physiological role in the synthesis of cell signal molecules. Dietary EPA and DHA accumulate in the membranes of cells where they are converted to anti-inflammatory eicosanoids and docosanoids, respectively. Both EPA and DHA can also inhibit production of pro-inflammatory eicosanoids produced from arachidonic acid (AA, C20:4 (n-6)). The ratio of pro-inflammatory to anti-inflammatory signal molecules is in turn controlled by dietary supply of n-6 and n-3 fatty acids. Although the ideal n-6 to n-3 ratio in the diet is not known, it is hypothesised to be around 3:1. However, the modern Western dirt has intakes of n-6 to n-3 fatty acids of between 6 and 10:1, which may lead to systemic inflammation and disease.
Current recommendations are therefore to increase intakes of n-3 fatty acids and decrease intakes of n-6 fatty acids. The essential fatty acid α-linolenic acid (ALA, C18:3 (n-3)) is produced in plants, but when consumed by humans is poorly metabolised to EPA and DHA. Therefore direct consumption of EPA and DHA is recommended. Fish are rich in EPA and DHA, with cold water fish such as mackerel, tuna, salmon and pilchards being particularly good sources. Increasingly the food industry is using fish from farmed sources to supply Western demand. The current recommendation to consume more of these fish is problematic however, because research shows that farmed fish may bioaccumulation antibiotics and other drugs which are used to keep the fish parasite free in their keep nets. As a result, recommendation is that farmed fish is limited in pregnant women or those at risk of becoming pregnant.
In addition, Research dating back over two decades suggests that farmed fish may be an inferior sources of n-3 fatty acids compared to their wild counterparts. For example, research published in the American Journal of Clinical Nutrition in 19901 investigated the n-3 fatty acid content of a number of varieties of wild fish and compared them to their farmed counterparts. The researchers collected 58 trout, 5 salmon and 51 eel from fishermen, or from hatcheries throughout Europe and analysed the flesh for n-3 and n-6 fatty acids using gas chromatography. The cultured eel and salmon contained 50 % more fatty acids than their wild counterparts, suggesting that the farmed fish were less healthy. For all species tested, the n-6 to n-3 fatty acid ratio was higher in the farmed fish, indicating that farmed fish are a poorer source of n-3 fatty acids.
These results suggest that farmed fish is not as nutritionally beneficial as wild fish in terms of n-3 fatty acid content. The ratio of n-6 to n-3 fatty acids in the wild compared to the farmed fish were 0.45 versus 0.16, 0.50 versus 0.21 and 0.18 versus 0.10, in trout, eel and salmon, respectively. This suggests that wild fish, although more expensive, may be more cost effective based on their fatty acid profiles. Eating wild fish provides the benefit of having to eat less flesh in order to receive the recommended intake of n-3 fatty acids. This reduces the exposure of the individual to other potentially toxic substances such as mercury and polychlorinated biphenyl, that are known to bioaccumulate in fish. Intakes of EPA and DHA should therefore only be derived from wild fish where possible. Tinned wild fish may be superior to fresh farmed fish.
RdB
