The eicosanoids and their relation with the essential fatty acids

This is a bit complicated, but please read slowly and check the connections with the previous posts.

Not very well known, the eicosanoids have roles in virtually every process in the body. Mainly they are binding to receptors on the surface and inside the cells. They can be categorized in prostaglandins (prostacyclins, thromboxanes) and leukotrienes (lipoxins).

The main substrate for eicosanoids synthesis is the arachidonic acid, resulted from the linoleic acid, one of the essential fatty oils. The prostaglandins synthesis from arachidonic acid, catalyzed by cyclo-oxigenase, can be inhibited by certain non-steroidal anti-inflammatory (Aspirine).

The other essential fatty acid - the linolenic acid - is transformed in EPA - a precursor for other eicosanoids synthesis - types that have more anti-inflammatory properties. We can mention Resolvins - which are made only from EPA.

In US and Norway, the main source for linolenic acid is soybean oil and its derivatives (tofu and other soybean-based products). EPA and DHA are obtained from krill and algae, but the real source is the algae producing the EPA/DHA, which is consumed by the krill, which in turn is eaten by the fishes. (30% of the fatty acids are in DHA form). In the infant formula all over the globe, the DHA  is coming from algae.

As you can see, i mentioned the essential fatty acids, the linoleic (part of the n-6 fatty acids family) and the linolenic acid (part of the n-3 fatty acids family). Those fatty acids need to be provided in diet, the lack of it can lead to poor growth and even death. They are essential because mammals cannot introduce double bonds beyond Carbon10 (counting from the carboxyl (end of the fatty acid). We cannot introduce Delta12 and Delta15, but we can make arachidonic acid (C20:4, N-6) from linoleic acid (C18:2:N-6) and EPA (C20:5,N-3) from linolenic acid ( C18:3, N-3).

The linoleic acid is a precursor for the arachidonic acid, source for various eicosanoids (functions in the body, pain management, immune function, blood pressure regulation and blood clotting). The linolenic acid is a precursor for EPA (eicosapentoic acid) and DHA (docosahexapentoic acid), serving to certains prostaglandins, such as the phospholipids in the brain and retina (from DHA). EPA and DHA can be found only in fatty fish and are sometimes reffered as fish oil fatty acids. A vegan or vegetarian diet will never have any EPA/DHA, so you will need to compensate by choosing good sources for linoleic and linolenic acids.