1.2 How Alcohol Affects the Body

Absorption, Metabolism, and BAC

To judge intoxication you need to understand the path alcohol takes through the body and the one rate that never changes: how fast the liver clears it. These mechanics explain why a guest can keep ordering, seem fine, and then spike rapidly.

How Alcohol Is Absorbed

Unlike food, alcohol needs no digestion. Roughly 20% is absorbed through the stomach lining and 80% through the small intestine, passing directly into the bloodstream. Effects typically begin 15 to 45 minutes after the first sip, and blood alcohol concentration (BAC) usually peaks 30 to 90 minutes after the last drink. That lag is dangerous: a guest who looks borderline now may climb higher 30 minutes after you stop serving.

Factors That Speed Up or Slow Down Absorption

The Liver Sets a Fixed Speed Limit

The liver metabolizes alcohol at a constant rate of roughly one standard drink per hour (about 0.015 BAC per hour). This is the single most tested concept in the chapter. Nothing accelerates it: not coffee, not cold showers, not exercise, not greasy food, not energy drinks, not vomiting. Only time lowers BAC. Coffee and energy drinks may make a guest feel alert, which is more dangerous because a "wide-awake drunk" still has impaired judgment and reflexes.

If a guest drinks faster than one standard drink per hour, the surplus alcohol circulates and BAC rises. Three standard drinks consumed in one hour means roughly two drinks' worth is still building in the bloodstream.

BAC and Observable Effects

Legal Limits You Must Know

• 0.08% BAC is the per se DUI limit in 49 states.
• 0.05% BAC is the limit in Utah, the strictest in the nation, effective December 30, 2018.
• 0.04% BAC applies to commercial drivers (CDL) nationwide.
• Zero tolerance (commonly 0.00 - 0.02%) applies to drivers under 21.

Note the exam trap: the older claim that "all states use 0.08%" is outdated. Utah moved to 0.05%.

Why Two Guests Reach Different BAC

• Body weight: a heavier person has more blood volume, diluting the alcohol, so lower BAC for the same intake.
• Body fat: fat tissue holds little water, so higher body-fat individuals reach higher BAC.
• Sex: women generally reach higher BAC than men of equal weight, due to less body water and lower levels of the alcohol-processing enzyme.
• Medications and food: some drugs amplify impairment; food slows the climb.

How the Body Processes Alcohol Chemically

Most alcohol metabolism happens in the liver in two enzyme steps. The enzyme alcohol dehydrogenase (ADH) converts ethanol to acetaldehyde, a toxic compound that causes much of the hangover and flushing reaction. A second enzyme, aldehyde dehydrogenase (ALDH), converts acetaldehyde into harmless acetate, which the body burns as energy or water and carbon dioxide. Because the supply of these enzymes is fixed, the rate is fixed. About 90 to 95% of alcohol is metabolized by the liver; the remaining small fraction leaves unchanged through breath, sweat, and urine, which is exactly what a breathalyzer measures.

Reading Visible Signs Tied to BAC

Servers cannot test BAC, so they read behavior. Map observable cues to the BAC ranges above:

These are the four classic warning categories most programs group as judgment, coordination, speech, and appearance. Two or more cues together signal you should stop service.

Common Exam Traps

• "Eating a big meal lowers BAC." False. Food only slows absorption; it does not reduce the total alcohol or speed metabolism.
• "A strong, fit person metabolizes alcohol faster." False. Fitness does not change liver enzyme rate.
• "Beer is safer than liquor." False. A standard beer and a standard shot contain the same 0.6 oz of pure alcohol.
• "Sleeping it off works fast." Only time matters; the rate is the same awake or asleep.

Server Takeaway

Because the liver clears only one drink per hour, the safest practical pace is no more than one standard drink hourly. When you stop service, BAC may still rise toward its peak for up to 90 minutes, so cut off before obvious intoxication, not after. Pair every signal you observe with the running standard-drink count from Section 1.1 to make a defensible service decision.