Metabolism of ethanol requires NAD+. Large amounts of alcohol generates NADH which is normally regarded as 'energy rich', but when produced in large quantities, it overwhelms the electron transport chain which is used to harness the energy.
Glycogen stores are depleted over hours. In the setting of high alcohol consumption and insufficient dietary carbohydrate, the depletion of NAD+ suppresses gluconeogenesis, driving generation of ketone bodies. An equilibrium exists between 3‑hydroxybutrate and acetoacetate (both ketone bodies), but the high [NADH] to [NAD+] ratio favours the formation of 3-hydroxybutrate.