Differences exist in the relationships between dietary linoleic and alpha-linolenic acids and their respective long-chain metabolites.

Increased concentrations of cellular eicosapentaenoic acid (EPA) have been shown to be beneficial in coronary heart disease, hypertension, and inflammatory disorders. Successful long-term strategies for increasing cellular EPA concentrations require information on the relationships between cellular concentrations of EPA and dietary amounts of alpha-linolenic acid (alpha-LA), a precursor of EPA, and dietary amounts of linoleic acid (LA), an antagonist of alpha-LA conversion to EPA. A dietary intervention study with healthy human volunteers that incorporated alpha-LA-rich vegetable oil (flaxseed oil), against a background diet low in LA, allowed us to examine these relationships. Linear relationships were found between dietary alpha-LA and EPA in plasma fractions and in cellular phospholipids. By contrast there was no relationship observed between dietary LA and tissue concentrations of its metabolite, arachidonic acid (AA). There was an inverse relationship between dietary alpha-LA and docosahexaenoic acid concentrations in the phospholipids of plasma, neutrophils, mononuclear cells, and platelets. The results indicate that increasing dietary alpha-LA will elevate tissue EPA concentrations in a predictable manner. This insight will facilitate the rational planning of practical dietary strategies for the long-term elevation of EPA concentrations in tissues.