Metabolism refers to all processes in the body that break down and convert ingested substances into the energy and nutrients needed to sustain life. Foods, liquids, and drugs all undergo metabolic processes within the body. Many foods are complex materials that need to be broken down into simpler substances, which in turn become “building blocks” for the body to use as needed. For example, protein is broken down into amino acids, which are used to build new proteins and regulate key metabolic reactions. Enzymes, are proteins that stimulate biochemical reactions for many metabolic processes. Whenever the function of an enzyme is altered, a metabolic disorder can develop. Metabolic disorders are important because they can affect energy production or damage tissues critical for survival. They may be inherited or acquired. Acquired metabolic disorders are more common and significant. Metabolic disorders may result in a substance rising to toxic levels (a storage disorder), or a necessary substance may not be produced, causing a deficiency.