Fatty Acid Structure and Synthesis

Fatty acid synthesis involves the de novo assembly of acetate into saturated fatty acids as well as the desaturation and elongation of the dietary essential fatty acids - linoleic acid (C18:2n-6) and α-linolenic acid (C18:3n-3) - to highly unsaturated 20- and 22-carbon fatty acids essential to reproduction, cell differentiation, inflammation, and cognition. Short-chain fatty acids are derived largely from bacterial fermentation such as that which occurs in the gut or rumen. Medium-chain fatty acids are characteristic of milk fat and are absorbed from the intestine directly into the portal blood, and subsequently metabolized largely by the liver. Fatty acids containing 14 or more carbons are absorbed from the intestine and transported to the periphery as chylomicrons. Very long chain fatty acids are largely found in neural tissue and used for myelin formation. Net fatty acid synthesis by humans is relatively small, but the de novo fatty acid biosynthetic pathway is essential for the production of malonyl-coenzyme A, a metabolite inhibitor of carnitine palmitoyltransferase. Consequently, substrate flux through the de novo lipogenic pathway plays a key role in determining if a fatty acid is partitioned to fatty acid oxidation or triglyceride assimilation.