Alcohol Metabolism

Alcohol Absorption & Metabolism

Alcohol is processed in the body through distinct steps: absorption, metabolism, and excretion. Unlike most nutrients, alcohol does not require digestion before absorption.

• Absorption:

  • Alcohol is absorbed directly through the stomach and small intestine lining into the bloodstream.

  • Most alcohol absorption occurs in the small intestine.

  • Once absorbed, alcohol is transported to the liver for metabolism.

• Metabolism:

  • Alcohol is metabolized primarily in the liver by specific enzymes.

  • The main pathway involves two key enzymes:

    • Alcohol dehydrogenase (ADH): Converts alcohol (ethanol) to acetaldehyde.

    • Aldehyde dehydrogenase (ALDH): Converts acetaldehyde to acetate.

  • Acetate can be used for energy by cells.

  • Acetaldehyde is toxic and must be quickly converted to acetate.

Equation for Alcohol Metabolism:

• Overall reaction:

Enzymes Involved in Alcohol Metabolism

• Alcohol dehydrogenase (ADH): Located mainly in the liver, initiates the breakdown of ethanol.

• Aldehyde dehydrogenase (ALDH): Also in the liver, converts acetaldehyde to acetate.

• Some metabolism occurs in the stomach, but the majority is in the liver.

Blood Alcohol Content (BAC)

Blood Alcohol Content (BAC) is the amount of alcohol in blood, expressed as a percentage. BAC is used to measure the degree of intoxication.

• Greater BAC = more alcohol in the body.

• BAC is influenced by several factors:

Factors Affecting Alcohol Absorption and BAC

• Body size: Smaller body size leads to higher BAC for the same amount of alcohol consumed.

• Body composition: More body fat results in higher BAC, as alcohol is less soluble in fat than in water.

• Sex: Females generally have higher BAC than males after consuming the same amount of alcohol, due to:

  • Lower body water percentage.

  • Lower activity of stomach ADH enzyme.

• Stomach contents: Food in the stomach slows alcohol absorption.

• Genetics: Some populations (e.g., Asians) have non-functional ALDH genes, leading to acetaldehyde buildup and "Asian flush".

Example: BAC Comparison

• Given two individuals (a female and a male) consuming the same amount of alcohol, the female will typically have a higher BAC due to lower body water and less active ADH enzyme.

• To lower BAC, one can:

  • Drink less alcohol.

  • Increase body water (e.g., by increasing body size).

  • Eat food before drinking.

Alcohol Metabolism Pathway Table

The following table summarizes the steps, enzymes, and locations involved in alcohol metabolism:

Key Points and Definitions

• Ethanol: The type of alcohol found in alcoholic beverages.

• Acetaldehyde: A toxic intermediate produced during alcohol metabolism.

• Acetate: A non-toxic product that can be used for energy by cells.

• Alcohol dehydrogenase (ADH): Enzyme that initiates alcohol breakdown.

• Aldehyde dehydrogenase (ALDH): Enzyme that detoxifies acetaldehyde.

• Blood Alcohol Content (BAC): Percentage of alcohol in the blood.

Additional info:

• Alcohol metabolism is a key topic in nutrition because it affects energy balance, nutrient absorption, and health risks associated with alcohol consumption.

• Impaired metabolism (e.g., due to genetic differences in ALDH) can lead to increased health risks.