The human body is typically dependent on glucose, a sugar, for energy; but it can also use stored fatty acids as an alternative. Oxidation of fatty acids is generally necessary for them to be an energy source; substances from the liver and the pancreas enable fats, or lipids, to pass from the intestinal walls into the blood stream. When fatty acids are oxidized, changes typically occur at the atomic level, which are initiated by various enzymes. The compounds also need to be activated within a cell’s cytoplasm; oxidation can then take place within cellular structures called mitochondria.
When it is required, the oxidation of fatty acids normally begins as an enzyme reacts with the molecules. An enzyme called carnitine can get the fatty compounds to cross over the membrane of the mitochondria, where the oxidation occurs. The movement of substances in and out of mitochondria is typically supported by the carnitine transport cycle. More energy per atom is typically produced than when carbohydrates are used for energy. Saturated fats and unsaturated fatty acids are usually oxidized in the same way, but the presence of a double atomic bond typically requires an additional enzyme during the oxidation of fatty acids.
Enzymes responsible for fatty acid oxidation can be activated by hormones. Cells typically release fat droplets into the blood; stored substances in the fat are broken up by enzymes beforehand. A lack of adequate food consumption and long exercise can trigger the body to start these reactions. In general, the products of enzyme reactions of fatty acids are moved into the mitochondria if the cell’s energy charge is low, while a high energy state will inhibit transport into the structures. Fat molecules are often used to create other substances and lipids for cell membranes instead.
In addition to energy, water is also produced during the oxidation of fatty acids. A reaction that breaks down oxygen and a chemical reaction with Adenosine Triphosphate (ATP) can both cause the formation of water. The extra component of this reaction often benefits animals living in dry climates or which hibernate.
Fatty acid oxidation sometimes occurs at a high rate; the liver can then react by producing energy molecules called ketone bodies. Imbalances, such as those that occur with diabetes, can lead to ketoacidosis, in which cells cannot oxidize large quantities of liver energy molecules and blood becomes too acidic. The normal oxidation of fatty acids from fish, soybeans, and seeds normally replenishes substances that the body does not produce on its own.