Alcohol Metabolism

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Alcohol Metabolism

Alcohol is absorbed into the blood from the gastrointestinal tract by passive diffusion. On consumption, a small amount of alcohol is absorbed in the mouth and stomach, but most of the absorption takes place in the small intestine. Usually, 30–45 minutes after consumption, the absorption of alcohol is at its maximum. The blood alcohol concentration (BAC) reached depends on several factors:

  • the amount consumed,
  • the rate at which the amount is consumed,
  • gender,
  • body mass,
  • recent food intake and
  • type of alcoholic beverage consumed.

The BAC reaches higher levels when both larger volumes of alcoholic beverages or higher alcohol percentage (ABV) are consumed. Alcohol is distributed from the blood into all tissues and fluids throughout the body in proportion to their relative content of water.

When drinking the same quantity of alcohol, women usually reach a higher BAC level than men, mostly because of their overall lower percentage of body water and higher percentage of body fat, and average lower body weight compared to men. Similarly, lean body mass and total body water is reduced in elderly individuals compared to younger individuals, leading to a relatively higher BAC[1].

Another important factor in predicting a person’s BAC level is recent food intake. The same amount of alcohol can produce a BAC as much as 50% lower in a person who has recently eaten compared with a person who is drinking on an empty stomach.  The balance between the absorption and breakdown of alcohol determines how the BAC changes over time. Most of the alcohol is metabolised for elimination by the liver. As described earlier, alcohol elimination is typically driven by specific alcohol-metabolising enzymes: alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH).  This enzyme system, however, becomes saturated at relatively low concentrations of alcohol.

Therefore, during periods of heavy and binge drinking, the liver’s microsomal ethanol oxidizing system (MEOS), an alternative pathway of alcohol metabolism, gets involved and breaks down the excess ingested ethanol to help clear the ethanol faster from the body. During this process, however, free radicals (very reactive oxygen molecules) are created which can damage the cells of the liver (Cederbaum 2012). 

[1] BAC = Blood alcohol concentration

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