Ketone bodies are three water-soluble compounds that are produced as by-products when
fatty acids are broken down for
energy in the
liver and
kidney. They are used as a source of energy in the
heart and
brain. In the brain, they are a vital source of energy during
fasting. Although termed "bodies", they are dissolved substances, not particles.
The three ketone bodies are acetone, acetoacetic acid, and beta-hydroxybutyric acid, although beta-hydroxybutyric acid is not technically a ketone but a carboxylic acid.
Ketone bodies can be used for energy. Ketone bodies are transported from the liver to other tissues, where acetoacetate and beta-hydroxybutyrate can be reconverted to acetyl-CoA to produce energy, via the citric acid cycle.
The heart gets little energy from ketone bodies; it uses mainly fatty acids.
