According to StudyBlue, ketogenic amino acids are the type that have been converted to acetoacetate or acetyl CoA and are the precursors of ketone bodies and fatty acids. Glucogenic amino acids are the type that have been converted to the precursors for the synthesis of glucose, such as pyruvate, oxaloacetate, fumarate, succinyl CoA and alpha-ketoglutarate. Certain types of amino acids are glucogenic and ketogenic, such as Isoleucine.
BioCarta notes that a large amount of metabolic energies is derived from amino acid metabolism. Amino acids that degrade into intermediates are known as glucogenic; some degrade directly into gluconeogenic intermediates and others contribute more indirectly to gluconeogenesis. The other common type of intermediates present in amino acid metabolism are acetoacetate and acetyl-CoA.
Animals do not have metabolic pathways that enable conversion of an intermediate into glucose. Animals use the metabolic processes of acetoacetate and acetyl CoA to produce ketone bodies or fatty acids. There are various amino acids that do not fall in a clean way into glucogenic or ketogenic. These are known as both glucogenic and ketogenic.
An example of an amino acid that is both glucogenic and ketogenic is an isoleucine metabolism that produces acetyl CoA, making it ketogenic. However, it additionally produces succinyl CoA, which is associated with glucose production.