Omega 3 (n-3) fatty acids are derived from two main dietary sources including seafood and certain nut and plant oils. As noted earlier, the primary marine-derived omega 3 fatty acids are EPA (C20:5n-3) and DHA (C22:6n-3) which are found in particularly high concentrations in deep water oily fish such as tuna, salmon, mackerel, herring, and cod. The plant-derived omega 3 fatty acid, ALA (C18:3n-3) is found in significant quantities in flaxseed and lesser amounts in canola, walnut and soybean.

Essential fatty acids (EFAs) are required in the diet as they can not be made by humans. The two established EFAs are linoleic acid (C18:2n-6, LA) and ALA. ALA can be converted in the body into EPA and DHA. LA is converted in the body to another long chain fatty acid arachidonic acid (AA) – both LA and AA are omega 6’s. Figure 1 shows the pathway of conversion of LA and ALA to their longer chain omega families.

AA and EPA are further metabolized to produce very powerful hormone-like substances (called ‘eicosanoids’) that effect physiological functions such as cell growth and division, inflammatory responses, muscle activity, blood pressure, and immune function. Eicosanoids formed from AA are released in the body in response to injury, infection, stress, or certain diseases. EPA forms eicosanoids that behave in opposition to those derived from AA and may help protect against heart attacks and strokes, as well as certain inflammatory diseases such as arthritis, lupus and asthma.

The conversion of ALA to EPA is very individual and will be affected by diet. A diet rich in LA can reduce ALA conversion by as much as 40%, and a high intake of LA by pregnant women lowers EPA and DHA levels in umbilical plasma, suggesting reduced ALA conversion and availability of omega 3 fatty acids for the developing fetus33. Other factors that interfere with ALA conversion include the intake of dietary cholesterol, saturated fat, and trans fatty acids. High intakes of omega 3 fatty acids can also block ALA conversion.

Kelley Fitzpatrick
Director of Health & Nutrition
Flax Canada