The three ketone bodies, each synthesized from acetyl-CoA molecules, are:
* Acetoacetate, which can be converted by the liver into β-hydroxybutyrate, or spontaneously turn into acetone.  Most acetoacetate is reduced to beta-hydroxybutyrate, which serves to additionally ferry reducing electrons to the tissues, especially the brain, where they are stripped back off and used for metabolism.
* Acetone, which is generated through the decarboxylation of acetoacetate, either spontaneously or through the enzyme acetoacetate decarboxylase. It can then be further metabolized either by CYP2E1 into hydroxyacetone (acetol) and then via propylene glycol to pyruvate, lactate and acetate (usable for energy) and propionaldehyde, or via methylglyoxal to pyruvate and lactate.
* β-hydroxybutyrate (not technically a ketone according to IUPAC nomenclature) is generated through the action of the enzyme D-β-hydroxybutyrate dehydrogenase on acetoacetate.  Upon entering the tissues, beta-hydroxybutyrate is converted by D-β-hydroxybutyrate dehydrogenase back to acetoacetate along with a proton and a molecule of NADH, the latter of which goes on to power the electron transport chain and other redox reactions.  β-Hydroxybutyrate is the most abundant of the ketone bodies, followed by acetoacetate and finally acetone.
β-Hydroxybutyrate and acetoacetate can pass through membranes easily, and are therefore a source of energy for the brain, which cannot directly metabolize fatty acids. The brain receives 60-70% of its required energy from ketone bodies when blood glucose levels are low. These bodies are transported into the brain by monocarboxylate transporters 1 and 2. Therefore, ketone bodies are a way to move energy from the liver to other cells. The liver does not have the critical enzyme,  succinyl CoA transferase, to process ketone bodies, and therefore cannot undergo ketolysis. The result is that the liver only produces ketone bodies, but does not use a significant amount of them.