A ketogenic amino acid is an amino acid that can be degraded directly into acetyl-CoA, which is the precursor of ketone bodies and "myelin, especially during early development, when brain myelin synthesis is extremely high" according to the National institute of Health. This is in contrast to the glucogenic amino acids, which are converted into glucose. Ketogenic amino acids are unable to be converted to glucose as both carbon atoms in the ketone body are ultimately degraded to carbon dioxide in the citric acid cycle.
In humans, two amino acids are exclusively ketogenic:
(remembered as all the "L" amino acids)
In humans, five amino acids are both ketogenic and glucogenic:
(remembered by the useful mnemonic "PITTT" or "FITTT", and includes all the aromatic amino acids)
Ketogenic amino acids serve important roles in the human body, leading to the study of ketogenic amino acid rich (KAAR) diets as possible treatment for non-alcoholic fatty liver disease (NAFLD) and diabetes. Dietary studies of fatty liver disease in mice show that decreasing the intake of ketogenic amino acids lysine and threonine may induce hepatic steatosis, a major cause of non-alcoholic fatty liver disease. Lysine in particular has been shown to serve an important role in the metabolic pathway for insulin via activation of the rapamycin complex 1 (mTORC1) and protein S6 kinase 1 (S6K1) for which over-activation leads to insulin resistance. Further studies illustrate that ketogenic amino acid rich diets may aid in decreasing obesity and insulin resistance, but their usage remains disputed.