MCADD stands for āmedium chain acyl-CoA dehydrogenase deficiency." It is one type of fatty acid oxidation disorder. People with these disorders have problems breaking down fat into energy for the body. MCADD occurs when an enzyme, called āmedium chain acyl-CoA dehydrogenaseā (MCAD), is either missing or not working properly. This enzymeās job is to break down certain fats in the food we eat into energy. It also breaks down fat already stored in the body. Energy from fat keeps us going whenever our bodies run low of their main source of energy, a type of sugar called glucose. Our bodies rely on fat when we donāt eat for a while ā such as when we miss a meal or when we sleep. When the MCAD enzyme is missing or not working, the body cannot use fat for energy, and must rely solely on glucose. Although glucose is a good source of energy, there is a limited amount available. Once the glucose has been used up, the body tries to use fat without success. This leads to low blood sugar, also called hypoglycemia, and to the build up of harmful substances in the blood.