BetaHydroxybutyrat

Beta-hydroxybutyrate, often abbreviated BHB, is one of the three primary ketone bodies produced by the liver. It arises during fatty acid breakdown in conditions such as prolonged fasting, carbohydrate restriction, or insulin deficiency and serves as an important energy substrate for peripheral tissues, including the heart and brain, when glucose availability is limited.

Chemically, beta-hydroxybutyrate is a hydroxy-keto carboxylic acid and exists as two enantiomers, D- and L-β-hydroxybutyrate. The D-enantiomer is the form most closely involved in human energy metabolism. It is generated from acetoacetate by the enzyme beta-hydroxybutyrate dehydrogenase using NADH, and it can be reconverted into acetyl-CoA inside mitochondria to fuel the tricarboxylic acid cycle.

In the body, BHB is transported in the blood and crosses the blood-brain barrier via monocarboxylate transporters, supplying energy to tissues when glucose is scarce. Beyond its role as fuel, BHB participates in signaling pathways, including inhibition of histone deacetylases and activation of certain G-protein-coupled receptors, which can influence inflammation, metabolism, and gene expression.

Exogenous forms of beta-hydroxybutyrate, such as ketone salts and esters, are consumed as dietary supplements to raise blood ketone levels. These supplements are used in some contexts to support ketosis, exercise performance, or cognitive function, though they can cause gastrointestinal discomfort and their physiological effects vary by formulation and dose.

Normal fasting BHB levels are typically 0.1–0.5 mM, with higher levels during sustained ketosis. Very high levels can occur in diabetic ketoacidosis. Beta-hydroxybutyrate remains a focus of nutritional and medical research for its metabolic and signaling roles.