Lhydroxybutyrate

L-hydroxybutyrate, commonly referred to as L-β-hydroxybutyrate or L-3-hydroxybutyrate, is the L enantiomer of the four-carbon hydroxycarboxylic acid 3-hydroxybutyrate. It is a stereoisomer of the more familiar D-β-hydroxybutyrate, which is one of the ketone bodies produced by the liver during fasting or carbohydrate-restricted states.

In humans, the D enantiomer (D-β-hydroxybutyrate) is the predominant circulating ketone body during ketosis. The L form generally occurs only in trace amounts in blood under normal conditions. Sources of L-hydroxybutyrate may include gut microbial metabolism, dietary intake of certain precursors, and potentially tissue- or microbial processes that generate or interconvert hydroxyfatty acids. The physiological significance of the L enantiomer is less well established than that of the D enantiomer.

Metabolically, the L enantiomer is thought to be less readily utilized for energy in human tissues than the D enantiomer, and its precise metabolic fate is not as well defined. Enzymes that act on 3-hydroxybutyrate can display enantioselectivity, and some pathways that handle hydroxybutyrates remain the subject of ongoing research. Some studies investigate L-hydroxybutyrate as a potential biomarker for gut microbiome activity or metabolic states, rather than as a major energy source.

In research and industrial contexts, L-hydroxybutyrate can serve as a chiral building block for chemical synthesis and as a reference in studies of hydroxycarboxylate metabolism.