The Journey of a Drink

From the moment alcohol touches your lips, your body starts a complex process. Understanding this process helps you make smarter decisions about drinking — and explains why the same number of drinks affects people so differently.

Mouth & Esophagus

A small amount of alcohol is absorbed through the mucous membranes in your mouth. This is why you might feel a slight warmth almost immediately. However, the vast majority passes through to your stomach.

Stomach

About 20% of alcohol is absorbed directly through the stomach lining. This is where food makes a big difference: an empty stomach allows rapid absorption (peak BAC in 30–45 minutes), while a full stomach can delay peak BAC by 1–2 hours. The stomach also performs “first-pass metabolism” — enzymes called alcohol dehydrogenase (ADH) begin breaking down alcohol before it ever reaches your blood.

Small Intestine

The remaining 80% of alcohol is absorbed in the small intestine, which has a much larger surface area than the stomach. Once absorbed, alcohol enters the bloodstream through the portal vein and heads straight to the liver.

Liver

Your liver is the primary organ responsible for breaking down alcohol. It processes alcohol at a roughly constant rate of 0.015–0.017% BAC per hour (about one standard drink per hour). The liver converts alcohol to acetaldehyde (toxic), then to acetate (harmless), then to water and CO2.

Brain

Alcohol crosses the blood-brain barrier easily. It enhances the effect of GABA (an inhibitory neurotransmitter) and suppresses glutamate (an excitatory one). This is why alcohol makes you feel relaxed at low doses but causes slurred speech, poor coordination, and impaired judgment at higher doses.

Factors That Affect Your BAC

Two people can drink the exact same amount and have very different BAC levels. Here’s why:

Body Composition (Most Important)

This is the single biggest factor most BAC calculators ignore. Alcohol distributes primarily in lean tissue (muscle, organs) and very little in fat tissue. Someone with more body fat has a smaller distribution volume, meaning the same amount of alcohol concentrates in less space — resulting in a higher BAC.

Biological Sex

Women generally reach higher BAC levels than men of the same weight after drinking the same amount. This is due to several factors:

• Higher average body fat percentage (smaller distribution volume)
• Lower levels of stomach ADH enzyme (less first-pass metabolism)
• Hormonal fluctuations that can affect alcohol metabolism
• Generally smaller liver size relative to body weight

Age

As you age, your body composition changes — lean mass decreases and fat mass increases, even if your weight stays the same. Liver function also gradually declines. This means the same drinking pattern that was “fine” at 25 may produce a noticeably higher BAC at 45.

Food in Your Stomach

Eating before or while drinking slows alcohol absorption significantly. Food (especially protein and fat) keeps the pyloric valve closed longer, keeping alcohol in the stomach where absorption is slower. This doesn’t reduce total absorption — it just spreads it out over time, resulting in a lower peak BAC.

Drink Type & Speed

Carbonated drinks (beer, champagne, mixed drinks with soda) are absorbed faster than non-carbonated ones. Drinking speed matters too — your liver can only process about one standard drink per hour. Drinking faster than that causes BAC to rise.

Hydration

Dehydration concentrates alcohol in a smaller blood volume, leading to a higher BAC. Alcohol itself is a diuretic (it makes you urinate more), which is why alternating alcoholic drinks with water is a smart strategy.

What is a “Standard Drink”?

In the United States, one standard drink contains approximately 14 grams of pure alcohol. This equals:

Metabolism Rate: What You Can and Can’t Control

Things that affect your metabolism rate

• Body weight — heavier people generally have larger livers and faster metabolism
• Age — liver efficiency decreases with age
• Sex — men have ~10% faster ADH enzyme activity on average
• Liver health — regular heavy drinking, fatty liver, and hepatitis all reduce metabolism rate
• Genetics — ADH and ALDH enzyme variants differ significantly across populations

Things that do NOT speed up metabolism

• Coffee — makes you feel more alert, does not lower BAC
• Cold shower — makes you feel more awake, does not lower BAC
• Exercise — negligible effect on alcohol metabolism
• Food after drinking — doesn’t help once alcohol is already absorbed
• Water — great for hydration, does not lower BAC

The US Body Composition Challenge

Why does Alcophone specifically calibrate for Americans? Because the US population has significantly different body composition averages than the European populations used to develop the original BAC formulas:

Using a formula calibrated for 1980s European body composition on a modern American adult can underestimate BAC by up to 25%. That’s the difference between “one more drink” and “over the legal limit.”