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The effects of the ω-3 and ω-6 essential fatty acids are characterized by their interactions.
Arachidonic acid is a 20-carbon ω-6 essential fatty acid. It sits at the head of the "arachidonic acid cascade" that initiates 20 different signaling paths that control a wide array of biological functions, including inflammation, cell growth and the central nervous system. Most AA in the human body is derived from dietary linoleic acid , found in nuts, seeds, vegetable oils and animal fats.
During inflammation two other groups of dietary essential fatty acids form cascades that compete with the arachidonic acid cascade. EPA provides the most important competing cascade. EPA is ingested from oily fish, algae oil, or alpha-linolenic acid. DGLA provides a third, less prominent cascade. It is derived from dietary GLA found in borage oil. These two parallel cascades soften the inflammatory promoting effects of specific eicosanoids made from AA.
Today, the typical diet in industrial countries contains much less ω-3 fatty acids than the diet of a century ago and a much greater amount of air pollution on a daily basis that evokes the inflammatory response. The diet from a century ago had much less ω-3 than the diet of early hunter-gatherers but also much less pollution than today. We can also look at the ratio of ω-3 to ω-6 in comparisons of their diets. These changes have been accompanied by increased rates of many diseases – the so-called diseases of civilization – that involve inflammatory processes. There is now very strong evidence that several of these diseases are ameliorated by increasing dietary ω-3. There is also more preliminary evidence showing that dietary ω-3 can ease symptoms in several psychiatric disorders.