Beta oxidation is a catabolic process by which fatty acid molecules are broken down in the cytosol in prokaryotes and in the mitochondria in eukaryotes to generate energy. It is a significant source of metabolic energy during interprandial periods and high energy demand states, such as exercise. The process involves a variety of enzymes, with the four main enzymes involved in fatty acid β-oxidation being acyl-CoA dehydrogenase, enoyl-CoA hydratase, hydroxyacyl-CoA dehydrogenase, and ketoacyl-CoA thiolase. The overall reaction for one cycle of beta oxidation is: Cn-acyl-CoA + FAD + NAD+ + H2O + CoA → Cn-2-acyl-CoA + FADH2 + NADH + H+ + acetyl-CoA. The process produces acetyl-CoA and an acyl-CoA that is two carbons shorter at the end of each cycle. The acetyl-CoA generated by the beta-oxidation pathway enters the mitochondrial TCA cycle, where it is further oxidized to generate NADH and FADH2. The NADH and FADH2 produced by both beta oxidation and the TCA cycle are used by the mitochondrial electron transport chain to produce ATP.