Organisms store excess energy as fatty acids and triglycerides. Under fasting conditions, fatty acids are oxidized in the mitochondria in a multi-step pathway called beta-oxidation (1). Beta-oxidation (or fatty acid oxidation) begins by importing long-chain fatty acids into the mitochondria, followed by a four-step reaction. In the first step, acyl-CoA dehydrogenase dehydrogenates the long-chain acyl-CoA. In the second step, enoyl-CoA hydratase hydrates the intermediate forming a hydroxy-acyl-CoA. In the third step, hydroxy-acyl-CoA dehydrogenase oxidizes the intermediate forming a keto-group. In the fourth step, thiolase cleaves acetyl-CoA and adds CoA to the new substrate, generating an acyl-CoA shortened by two carbons. This cycle is repeated until the entire chain is oxidized into acetyl-CoA.