A Review of the Effects of Alcohol on Carbohydrate Metabolism

Abstract

1. The effects of alcohol (ethanol) on carbohydrate metabolism are reviewed. 2. The metabolism of ethanol by alcohol dehydrogenase leading to a decreased [NAD+]/[NADH] ratio plays an important role in the above effects of ethanol in the liver, whereas effects in brain and other tissues could be caused by acetaldehyde transported from the liver. 3. Ethanol increases peripheral acetate utilization and decreases free coenzyme A in brain. 4. Ethanol inhibits hepatic gluconeogenesis by decreasing the steady-state concentration of pyruvate. 5. Ethanol inhibits glycolysis in liver and brain. In the liver, the inhibition may be at the level of 3-glyceraldehyde phosphate dehydrogenase. 6. Ethanol inhibits the tricarboxylic acid cycle by an undefined mechanism(s) involving decreased pyruvate concentration, increased malate/oxaloacetate ratio or inhibition of citrate synthase and isocitrate dehydrogenase. 7.Ethanol inhibits the pentose phosphate pathway in the liver, but enhances that in the brain. The mechanisms of these actions require investigation. 8. Ethanol causes an initial hyperglycaemia, a later hypoglycaemia and various effects on glucose utilization. 9. Ethanol inhibits galactose metabolism by inhibiting the key enzyme uridine diphosphate galactose 4-epimerase. 10. Ethanol inhibits the metabolism of fructose and sorbitol. 11. It is suggested that further work is required to examine the roles of acetaldehyde and of pyridine nucleotides in the actions of ethanol on brain carbohydrate metabolism.