Fish oils are good source of the long chain fatty acids eicosapentaenoic acid (EPA, C20:5 (n-3)) and docosahexaenoic acid (DHA, C22:6 (n-3)). These long chain fatty acid feed into the omega-3 pathway, of which alpha linolenic acid (ALA, C18:3 (n-3)) is the starting substrate, and provide a source for the production of eicosanoids hormones that regulate inflammation. This pathway explains the anti-inflammatory effects of fish oils. However, DHA is available from algae, and this form is produced commercially. Vegetarians that are unable to consume fish, or individuals who are worried about the pollution in fish oil, may choose to derive their DHA from algal sources rather than fish oils. However, while fish oils provide both EPA and DHA, algae provide only DHA. Although DHA is theoretically interconvertible with EPA in the essential fatty acid pathway, it is becoming clear that EPA and DHA have distinct roles in human nutrition. Fish oils and algal oils may therefore differ in their biochemical effects.
Direct comparisons between DHA from algal sources and DHA and EPA for fish oils is limited, but a number of studies have approached the issue. For example, in one study1, researchers compared the effects of four fat treatments that were included as meals in the diets of 16 healthy men. The meals consisted of a high oleic acid sunflower meal, a high oleic sunflower and fish oil meal (EPA and DHA rich), a high oleic sunflower and algal meal (DHA rich) or a high linoleic acid sunflower meal (high in linoleic acid). Each subject consumed each of the meals, which was composed of 75 grams fat, 93 grams carbohydrate and 14 gram protein, on separate occasions. Consumption of the fish oil meal resulted in a significant increase in plasma levels of EPA and DHA. In contrast, the algal meal resulted in an increase in plasma levels of DHA only. Total omega-3 fatty acid plasma levels increased 174 % with fish oils but only 106 % with algal oil, despite both providing the same total amount of omega-3 fatty acids.
In addition, the fish oils and algal oils also caused reductions in pulse wave reflection, with the greatest reduction being evident 2 hours postprandially. Pulse wave reflection relates to arterial stiffness and wave reflection changes as arterial stiffness increases and diameter decreases. The implication is that fish oil and algal oils may be beneficial in this regard. Increases in 8-isoprostane F2α were also recorded after consumption of the sunflower and fish oil meals, but not the algal oil meal. Isoprostanes are useful markers of oxidative stress and the implication from this result is that fish oil and sunflower oil, but not algal oil, may increases levels of lipid peroxidation following consumption. This may suggest that the algal oils are less prone to cause lipid peroxidation compared to fish oil, perhap because the oil is better protected and less oxidised in its supplemental form, and therefore less likely to propagate free radical generation. Algal oils may therefore be a better form of omega-3 fatty acids compared to fish oils.