Alpha-Linolenic Acid

Alpha-linolenic acid (ALA) is an essential polyunsaturated fatty acid containing 18 carbon atoms and three cis double bonds. It is written in fatty-acid shorthand as 18:3 n-3, or 18:3 omega-3. The omega-3 designation means that the first double bond is located at the third carbon when counted from the methyl end of the fatty-acid chain .^1,2

ALA is essential because humans cannot synthesize it and must obtain it from the diet. Once absorbed, it can be incorporated into complex lipids such as phospholipids, oxidized for energy, or used as a precursor for longer-chain omega-3 fatty acids .^2,3

Through a series of desaturation and elongation reactions, ALA can be converted to eicosapentaenoic acid (EPA) and, through further metabolism, to docosahexaenoic acid (DHA). In humans, however, this conversion is limited, particularly for DHA. ALA, EPA, and DHA therefore belong to the same omega-3 family but are distinct fatty acids with different structures and metabolic fates .^2,3

Alpha-linolenic acid should not be confused with linoleic acid. Both are essential 18-carbon polyunsaturated fatty acids, but ALA has three double bonds and belongs to the omega-3 family, whereas linoleic acid has two double bonds and belongs to the omega-6 family. Humans cannot convert omega-3 fatty acids into omega-6 fatty acids or vice versa .^2,3