Ketoaciosis is a type of metabolic acidosis which is caused by high concentrations of ketone bodies, formed by the deamination of amino acids, and the breakdown of fatty acids. The two common ketones produced in humans are acetoacetic acid and β-hydroxybutyrate. This is most common in untreated type 1 diabetes mellitus, when the liver breaks down fat and proteins in response to a perceived need for respiratory substrate. It can also occur with people undergoing hunger strikes, fasting over 3 days, or people starving to death as the body is forced to break down fat for sustenance due to their lack of outside nutrition. Ketoacidosis can be smelled on a person's breath. This is due to acetone, a direct byproduct of the spontaneous decomposition of acetoacetic acid. It is often described as smelling like fruit or nail polish remover.