Fish oils are a good source of the long chain fatty acids eicosapentaenoic acid (EPA, C20:5 (n-3)) and docosahexaenoic acid (DHA, C22:6 (n-3)). These fatty acids feed into the omega-3 fatty acid pathway where they provide substrates for the production of important eicosanoid and docosanoid signal molecules that are involved in the regulation of cellular functions, including the inflammatory response. Fish oils are useful because the Western diet contains too much omega-6 fat in comparison to omega-3 fat and this causes the generation of pro-inflammatory conditions in cells and tissues, which can be a cause of systemic inflammation and oxidative stress. Consuming fish oils rebalances the omega-6 to omega-3 fatty acid ratio and this can produce an antiinflammatory effect. However, fish oils may contain pollutants which are known to bioaccumulate in fish. Therefore alternative sources of the omega-3 fatty acids EPA and DHA, which are pollutant free, are of interest nutritionally.
One possible source of DHA is algal oils. Alga produce DHA and when the algae are consumed by fish this fatty acid accumulates in tissues, whereby some of it is converted to EPA. Consumption of algal oil has been studied in humans, and in one study1 results showed an increase in plasma levels of DHA, but not EPA following consumption. In comparison fish oils result in increases in plasma levels of both EPA and DHA. Although DHA in the tissues of humans can ultimately be converted to EPA and then to cellular eicosanoids, through activation of an elongase and desaturase enzyme, this process may not be as efficient as consuming a direct source of the EPA. Another alternative to fish oils might be the consumption of krill oil. Krill are small crustaceans that consume algae, and in the process accumulate both EPA and DHA in their tissues. Oil produced from krill is therefore a dietary source of both EPA and DHA, and consumption of this oil may increase tissue levels of both DHA and EPA in humans.
For example, in one study2 researchers administered krill oil (from Euphausia superba) at a dosage of 2 grams per day to overweight men and women for 4 weeks. Some subjects were administered either menhaden fish oil (containing both EPA and DHA) or olive oil (no DHA or EPA) as positive and negative control groups, respectively. As hypothesised, the plasma EPA and DHA levels increased significantly more in the fish oil and krill oil groups compared to the olive oil group. In this regard, EPA increased 178.4 μmol/L and 131.8 μmol/L, and DHA increased 90.2 μmol/L and 149.9 μmol/L in the krill and menhaden groups, respectively. Systolic blood pressure decreased significantly more in the fish oil group (-2.2 mm Hg) compared to either the krill oil (-0.8 mmHg) or olive oil groups (+3.3 mm Hg). As with algal oil, krill oil therefore appears to produce some slight biochemical differences to fish oils, and these should be taken into consideration when deciding on a supplemental form of omega-3 fatty acids.
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