Microsomal Ethanol Oxidizing System

The Microsomal Ethanol Oxidizing System (MEOS) is an alternate pathway of ethanol metabolism to the oxidation of ethanol via alcohol dehydrogenase. While playing only a minor role in ethanol metabolism in average individuals, MEOS activity increases after chronic alcohol consumption. Increase in MEOS activity is correlated with an increase in cytochrome P450, particular CYP2EI, seen most conclusively in alcohol dehydrogenase negative deer mice.

The MEOS pathway requires oxidation of NADPH to NADP, which consumes ATP and dissipates heat, thus leading to the hypothesis that long term drinkers see an increase in resting energy expenditure.