They are major sources of energy. Most diets contain a great deal of fatty acid in the form of triacylglycerol (esters with glycerol). Some of our dietary carbohydrate is converted to fat -- stored as triacylglycerol in adipose tissue. Subsequently the fatty acids from this fat are released to provide energy for various aerobic tissues.They are precursors of essential substances in the body (structural and metabolic). For example, phospholipids are essential components of all cell membranes and of plasma lipoproteins, and the essential fatty acids are precursors of prostaglandins and related regulators.Defects in fatty acid metabolism are involved in diseases. Defects in the mitochondrial acyl CoA dehydrogenases, for example, prevent normal fatty acid oxidation.