Dhydroxybutyrate

D-hydroxybutyrate, also known as D-β-hydroxybutyrate (D-BHB) or D-3-hydroxybutyrate, is a four-carbon hydroxycarboxylic acid and one of the ketone bodies produced during fatty acid oxidation. It exists as two enantiomers, D and L, with the D enantiomer being the physiologically dominant form in humans.

Biochemistry and metabolism: During prolonged fasting or carbohydrate restriction, the liver increases ketogenesis, producing ketone bodies from acetyl-CoA. Acetoacetate can be reduced to D-BHB by a dehydrogenase, and D-BHB is released into the bloodstream. It is transported to peripheral tissues via monocarboxylate transporters and, once inside cells, is converted back to acetyl-CoA to enter the tricarboxylic acid cycle for energy production.

Physiological role: D-BHB serves as an important energy substrate when glucose availability is limited, supporting energy supply for the brain, heart, and skeletal muscle. It can cross the blood-brain barrier and, under certain conditions, provides more efficient energy per carbon than glucose. In addition to its metabolic role, D-BHB is being studied as a signaling molecule that may influence various cellular pathways, though many of these roles remain an area of active research.

Clinical and research context: Elevated D-BHB levels occur in physiological ketosis and in diabetic ketoacidosis. Measurement of ketone bodies, including D-BHB, is used diagnostically in metabolic investigations. Exogenous ketone supplements containing D-BHB–related forms are marketed for potential therapeutic or performance-enhancing effects, but evidence for specific benefits varies by context.