Any of three compounds, acetoacetic acid (3-oxobutanoic acid, CH₃COCH₂COOH), β‎-hydroxybutyric acid (3-hydroxybutanoic acid, CH₃CH(OH)CH₂COOH), and acetone (propanone, CH₃COCH₃), all produced by the liver as a result of the metabolism of body fat deposits. Ketone bodies are normally used as energy sources by peripheral tissues. However, if carbohydrate supply is limited (e.g. during starvation or in diabetics), the blood level of ketone bodies rises and they may be present in urine, giving it a characteristic ‘pear drops’ odour. This condition is called ketosis.