Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health, but cannot synthesize them.
Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid). These are supplied to the body either as the free fatty acid, or more commonly as some glyceride derivative. Deficiency in these fatty acids is rare. These fatty acids are essential because they are precursors to vitamins, cofactors, and derivatives, including prostaglandins, leukotrienes, thromboxanes, lipoxins, and others.
When the two EFAs were discovered in 1923, they were designated "vitamin F", but in 1929, research on rats showed that the two EFAs are better classified as fats rather than vitamins.
In the body, essential fatty acids serve multiple functions. In each of these, the balance between dietary ω-3 and ω-6 strongly affects function.
They are modified to make
the classic eicosanoids (affecting inflammation and many other cellular functions)
the endocannabinoids (affecting mood, behavior and inflammation)
the lipoxins which are a group of eicosanoid derivatives formed via the lipoxygenase pathway from ω-6 EFAs and resolvins from ω-3 (in the presence of acetylsalicylic acid, downregulating inflammation)
the isofurans, neurofurans, isoprostanes, hepoxilins, epoxyeicosatrienoic acids (EETs) and neuroprotectin D
They form lipid rafts (affecting cellular signaling)
They act on DNA (activating or inhibiting transcription factors such as NF-κB, which is linked to pro-inflammatory cytokine production)
Fatty acid#Nomenclature
Fatty acids comprise an aliphatic hydrocarbon chain plus a carboxyl group (–COOH) at one end, and terminated by a methyl group (–CH3) at the other end. They are almost always straight-chained. The carbon next to the carboxylate is known as α, the next carbon β, and so forth. Since biological fatty acids can be of diverse lengths, the last position is often labelled as a "ω", the last letter in the Greek alphabet.