During amino acid catabolism, the removal of the amino group leaves a carbon skeleton. These carbon skeletons are converted into one of seven major metabolic intermediates: pyruvate, acetyl CoA, acetoacetyl CoA, alpha-ketoglutarate, succinyl CoA, fumarate, or oxaloacetate. The liver utilizes these metabolites for multiple purposes, including energy production via the citric acid cycle, acting as anabolic precursors, or generating ketone bodies and glucose. Consequently, amino acids are categorized as ketogenic, glucogenic, or both, depending on which metabolic pathways their carbon skeletons enter.