Elaidic acid is a chemical compound with the formula C18H34O2, specifically the fatty acid with structural formula HOOC−(CH2)7−CH=CH−(CH2)7−CH3, with the double bond (between carbon atoms 9 and 10) in trans configuration.

This compound has attracted attention because it is a major trans fat found in hydrogenated vegetable oils, and trans fats have been implicated in heart disease.

Its name comes from the Ancient Greek word ἔλαιον (elaion), meaning oil.

[2] It's also present in small amounts in caprine and bovine milk (very roughly 0.1% of the fatty acids)[3] and in some meats.

[4] Elaidic acid increases plasma cholesterylester transfer protein (CETP) activity which lowers HDL cholesterol.