Omega-9 fatty acid

Omega-9 fatty acids are a class of unsaturated fatty acids that have a C=C double bond in the &omega;-9 position. (See Nomenclature for terms and discussion of &omega; (omega) nomenclature.) Some &omega;-9s are common components of animal fat and vegetable oil.

Two &omega;-9 fatty acids important in industry are:
 * Oleic acid (18:1 &omega;-9), which is a main component of olive oil and other monounsaturated fats
 * Erucic acid (22:1 &omega;-9), which is found in rapeseed, wallflower seed, and mustard seed. Rapeseed with high erucic acid content is grown  for commercial use in paintings and coatings as a drying oil.

Unlike &omega;-3 and &omega;-6 fatty acids, &omega;-9 fatty acids are not classed as essential fatty acids  (EFA). This is both because they can be created by the human body from unsaturated fat, and are therefore not essential in the diet, and because the lack of an &omega;-6 double bond keeps them from participating in the reactions that form the eicosanoids.

Under severe conditions of EFA deprivation, mammals will elongate and desaturate oleic acid to make mead acid, (20:3 &omega;-9). (Lipomics) This also occurs to a lesser extent in vegetarians and semi-vegetarians. (Phinney, 1990)