Ketogenic Amino Acids.

Leucine is one of only two amino acids whose carbon skeleton is entirely ketogenic, degrading through HMG-CoA to acetoacetate and acetyl-CoA. It is the largest contributor to the ketogenic amino acid pool.

Lysine is the second purely ketogenic amino acid, catabolised by the saccharopine route to acetoacetyl-CoA. Its carbon never enters gluconeogenesis.

HMB is a metabolite of leucine formed on the way to HMG-CoA. Supplying it enters the same ketogenic branch further downstream.

The branched-chain ketoacid dehydrogenase complex needs thiamine pyrophosphate at its E1 subunit to decarboxylate the ketoacids. Without it the ketogenic branch stalls at the ketoacid step.

Riboflavin supplies the FAD used by the branched-chain dehydrogenase E3 subunit and by the acyl-CoA dehydrogenases downstream. Both steps sit on the route to acetoacetate.

Pyridoxal-5-phosphate is the cofactor for the branched-chain aminotransferase that starts the catabolic sequence. Transamination happens before any carbon reaches the ketone route.

Methylcrotonyl-CoA carboxylase, a step unique to leucine breakdown, is a biotin-dependent carboxylase. Biotin status governs how completely leucine carbon reaches HMG-CoA.

Every intermediate in this catabolic route travels as a coenzyme A thioester, and pantothenate is the backbone of CoA. Adequate CoA keeps the acyl intermediates moving.

Carnitine carries accumulating short and branched acyl groups out as acylcarnitines and frees coenzyme A. That keeps the CoA pool available for continued catabolism.

Medium-chain fats are taken to the liver and converted to acetoacetate and beta-hydroxybutyrate, the same ketone bodies this amino acid carbon feeds. The two inputs converge on one pool.

An exogenous ketone salt supplies the end product that ketogenic amino acid catabolism generates internally. Circulating ketone concentration reflects both contributions.

Isoleucine is split between glucogenic and ketogenic ends, and its ketogenic half runs through the same branched-chain ketoacid dehydrogenase step. The three branched-chain amino acids share that single enzyme complex.

Methylmalonyl-CoA mutase needs adenosylcobalamin, and it sits on the catabolic route of the glucogenic branched-chain amino acids valine and isoleucine. Leucine, the purely ketogenic one, does not pass through that step. In a mixed amino acid formula B12 status determines whether the glucogenic half of the blend clears normally.

NAD+ is the electron acceptor for the branched-chain ketoacid dehydrogenase complex and for the dehydrogenase steps further down leucine and lysine catabolism. Niacin is the dietary precursor of that NAD+ pool. Without adequate NAD+ the pathway backs up at the first irreversible step.

Lipoamide is a covalently bound cofactor of the E2 component of the branched-chain ketoacid dehydrogenase complex, the same architecture as pyruvate dehydrogenase. Lipoic acid is the free form of that cofactor. This is a settled cofactor relationship rather than a supplement effect claim.

Branched-chain ketoacid dehydrogenase activity is set by a kinase and a phosphatase, both ATP and magnesium dependent, and every ATP-using step downstream needs magnesium as the counter-ion. Separately, a ketogenic dietary state increases urinary loss of magnesium along with sodium and potassium. Both reasons put magnesium next to ketogenic amino acids in a formula.

The fall in insulin during a ketogenic state reduces renal sodium reabsorption, and the resulting natriuresis carries potassium with it. That is textbook renal physiology, not a supplement claim. Formulas built for a ketogenic context pair amino acids with potassium for this reason.

Sodium loss is the earliest and largest electrolyte shift when carbohydrate intake drops and insulin falls. Most of the symptoms people report in the first days of a ketogenic diet track that shift. Amino acid intake does not cause it and does not correct it, so sodium is a companion rather than an interaction.

A combined sodium, potassium and magnesium product covers the three minerals a low-insulin state moves at once. Pairing it with a ketogenic amino acid blend is standard formulation practice for that context. The electrolytes address fluid and mineral handling; the amino acids address protein turnover, and neither substitutes for the other.

Tryptophan is both ketogenic and glucogenic: part of its carbon skeleton reaches acetoacetyl-CoA, part reaches pyruvate and alanine. It is also the precursor for de novo NAD+ synthesis, which the ketogenic pathway itself consumes. Including it changes the ketogenic-to-glucogenic balance of a blend rather than adding to the ketogenic side alone.

Tyrosine catabolism splits cleanly into two products: fumarate, which is glucogenic, and acetoacetate, which is ketogenic. So it belongs in both categories at once. In a formula it broadens the amino acid profile without being a source of ketone bodies alone.

Phenylalanine hydroxylase converts phenylalanine to tyrosine, after which the two share the same fate of fumarate plus acetoacetate. Its ketogenic contribution is entirely downstream of that conversion. That makes it a dual-classified amino acid like tyrosine, not a purely ketogenic one.

Valine is the purely glucogenic branched-chain amino acid: its skeleton ends at succinyl-CoA, not acetyl-CoA. It competes with leucine both for the LAT1 transporter at the blood-brain barrier and for the shared branched-chain aminotransferase and dehydrogenase enzymes. Raising valine therefore lowers the fraction of that shared machinery working on leucine.

Glutamine is a major anaplerotic and gluconeogenic substrate, entering the cycle at alpha-ketoglutarate and exiting toward glucose. At larger intakes it supplies carbon for glucose in a way a purely ketogenic amino acid cannot. Whether that measurably shifts circulating ketone concentrations at supplement doses has not been established, so the direction is mechanistic.

Glycine conjugation is how the body disposes of isovaleryl-CoA, an intermediate of leucine catabolism, exporting it as isovalerylglycine. So glycine availability is part of the clearance route for a purely ketogenic amino acid. Glycine's own carbon skeleton, by contrast, is glucogenic.

Carnitine is built from lysine, and the two hydroxylation steps in that biosynthesis are ascorbate-dependent dioxygenases. Lysine is one of the two purely ketogenic amino acids, so this links its supply directly to fatty acid transport capacity. It is a settled cofactor relationship with no citation needed.

The same hydroxylases that build carnitine from lysine are non-heme iron enzymes, working alongside ascorbate. Iron status therefore sits on the lysine-to-carnitine route as well. This is enzymology, not a claim that iron raises carnitine in a person.

Whey is the richest common protein source in leucine, so it delivers the ketogenic amino acid alongside the full glucogenic complement and is markedly insulinotropic. That insulin response is the reason a whey dose behaves differently from an isolated leucine dose in a low-carbohydrate context. Stacking them raises total leucine but also raises everything else.

Casein clots in gastric acid and empties slowly, producing a lower, longer rise in plasma amino acids than whey. Paired with free-form leucine the two cover different parts of the same window. The trade is peak aminoacidemia against duration, not one being better.

Creatine works on phosphocreatine resynthesis and cell hydration; leucine works through mTORC1 signalling and substrate supply. The two support lean mass by unrelated routes, which is why they appear together in energy-restricted and low-carbohydrate protocols. Creatine synthesis also draws on glycine, arginine and methionine, so an amino acid blend touches its precursor pool.

Threonine is degraded by more than one route, and depending on which dominates its carbon reaches acetyl-CoA or succinyl-CoA. That places it in both the ketogenic and glucogenic columns. It is worth naming because textbooks list it inconsistently and a blend's classification depends on which route is assumed.

Histidine is glucogenic through glutamate and alpha-ketoglutarate. Like methionine it dilutes any claim that a blend is purely ketogenic. It is named here for accuracy about what the category means, not as a performance pairing.

Every amino acid oxidised for carbon has to have its nitrogen removed, and that nitrogen leaves as urea through a cycle in which arginine is an obligatory intermediate. Higher amino acid oxidation therefore means more urea cycle flux. Naming this makes clear that ketogenic amino acids are not nitrogen-free fuel.

Ornithine is the carrier that accepts the carbamoyl group at the start of each turn of the urea cycle, so it is part of how nitrogen from oxidised amino acids is disposed of. This is a cofactor-style relationship rather than a claim that supplemental ornithine increases anything. It belongs in any honest account of what happens to the nitrogen.

Beta-alanine raises muscle carnosine and buffers intracellular acidity during high intensity work; it is not a protein-forming amino acid and contributes no ketogenic carbon. It is named here because it shares a shelf with ketogenic amino acid products, not because the mechanisms interact. Untested as a pair.