The ketone bodies are three chemical compounds: 3-oxobutanoic acid (acetoacetic acid), 3-hydroxybutanoic acid (β-hydroxybutyric acid), and propanone (acetone). When present in the blood in high concentrations, they increase the blood's acidity. Known as ketonuria or ketosis, this condition occurs most commonly in starvation (see malnutrition) and diabetes mellitus.
The ketone bodies are products of poor carbohydrate metabolism, and they accumulate in the body tissue and fluids, especially the urine. Note that β-hydroxybutyrate is not chemically a ketone; however, it is considered to be physiologically equivalent to one because it and acetoacetate are readily interconverted in the body.
A ketogenic diet is a diet that promotes the formation of ketone bodies (called ketogenesis) in the tissues. It is one in which the principal energy sources is fat rather than carbohydrate.