Figure 1. Diagrammatic representation of the mitochondrial fatty acid β-oxidation. During β-oxidation in the mitochondria, free fatty acids (FFAs) undergo step-wise enzymatic dehydrogenation, hydration, a second dehydrogenation, and thiolysis to generate a single 2-carbon acetyl-CoA molecule and a shortened fatty acid. The cycle is repeated until the fatty acid is completely broken down into its constituent acetyl-CoA subunits. The acetyl-CoA molecules enter the citric acid cycle to produce energy-rich NADH and FADH2 molecules that are then converted to ATP in the electron transport chain. Under fasting conditions, acetyl-CoA molecules are converted into ketone bodies (acetoacetate and β-hydroxybutyrate), which are released by the liver to be oxidized in peripheral tissues by the tricarboxylic acid cycle. CPT: carnitine palmitoyl transferase; TCA: tricarboxylic acid.