Editing Essential fatty acid (section)

===Examples===
[[Polyunsaturated fatty acid]]s with 16- and 18-carbon chains are sometimes classified as '''short chain polyunsaturated fatty acids''' ('''SC-PUFA'''), as opposed to '''long-chain polyunsaturated fatty acids''' ('''LC-PUFA'''), which have more than 18 carbon atoms.<ref name=PUFA>{{cite journal |vauthors=Buckley MT et al. |title=Selection in Europeans on Fatty Acid Desaturases Associated with Dietary Changes |journal=Mol Biol Evol |volume=34 |issue=6 |pages=1307–1318 |year=2017 |pmid=28333262 |pmc=5435082 |doi=10.1093/molbev/msx103}}</ref>

Both the essential fatty acids are SC-PUFA with an 18-carbon chain:
* [[omega-3 fatty acid|ω−3 fatty acid]]:
** [[alpha-linolenic acid|α-linolenic acid]] or ALA (18:3n−3)
* [[Omega-6 fatty acid|ω−6 fatty acid]]:
** [[linoleic acid]] or LA (18:2n−6)
These two fatty acids cannot be [[Biosynthesis|synthesized]] by humans because humans lack the [[desaturase]] [[enzymes]] required for their production.

They form the starting point for the creation of more desaturated fatty acids, most of which also have a longer carbon chain:
* [[omega-3 fatty acid|ω−3 fatty acid]]s:
** [[eicosapentaenoic acid]] or EPA (20:5n−3)
** [[docosahexaenoic acid]] or DHA (22:6n−3)
* [[Omega-6 fatty acid|ω−6 fatty acids]]:
** [[gamma-linolenic acid]] or GLA (18:3n−6)
** [[dihomo-gamma-linolenic acid]] or DGLA (20:3n−6)
** [[arachidonic acid]] or AA (20:4n−6)
Except for GLA, which has a short 18-carbon chain, these fatty acids have more than 18 carbon atoms and are typically classified as LC-PUFA.<ref name=PUFA />

[[Omega-9 fatty acid|ω−9 fatty acids]] are not essential in humans because they can be synthesized from carbohydrates or other fatty acids.