5.3 Factors Affecting Alcohol Absorption Rates

Why Absorption Rate Matters More Than Drink Count

Section 5.2 explained that the same drink count produces different BACs in different people because of who they are. This section explains that the same drink count can produce different BACs in the same person depending on how, when and what they drink. Together these factors are why the duty manager's lawful test is observation of the individual, not the till receipt.

Food in the Stomach

Food is the single biggest controllable factor in how fast alcohol reaches the bloodstream.

• Eating before or during drinking — especially food containing fat and protein — slows gastric emptying (the rate at which the stomach releases contents to the small intestine, where most alcohol is absorbed). The alcohol is held in the stomach longer, metabolised by gastric ADH, and released more slowly. The result is a lower peak BAC for the same number of drinks.
• Drinking on an empty stomach — alcohol passes quickly to the small intestine and is absorbed rapidly, producing a fast, high peak.

This is not just theory: the host-responsibility requirement under the Sale and Supply of Alcohol Act 2012 that on-licence and club premises make food available whenever alcohol is being sold is partly grounded in this physiology. Encouraging patrons to eat is a recognised intoxication-prevention strategy.

Rate of Drinking

Because the liver metabolises alcohol at a fixed rate (~1 standard drink per hour), the rate at which a patron drinks relative to that fixed clearance is decisive:

• Rapid consumption (shots, drinking games, 'skulling') overwhelms the liver's clearance capacity and BAC climbs sharply.
• Spacing drinks (one per hour or slower) lets metabolism keep up, so BAC rises slowly and may plateau at a much lower level.

A practical duty-manager cue: a patron who orders doubles, drinks in quick succession, or is seen to finish a drink in a few minutes is on a fast-rising curve even if their current visible signs are mild.

Carbonation

Carbonated drinks are absorbed faster than still drinks of the same alcohol content. The pressure from the dissolved gas appears to push alcohol through the stomach lining and speed gastric emptying. Common examples:

• Champagne and sparkling wine
• Beer (naturally carbonated)
• Spirits mixed with fizzy soft drinks (bourbon and cola, vodka and soda)

A still version of the same drink (e.g. wine without bubbles, spirits with juice) tends to produce a slower, lower peak.

Body Size and Composition

Alcohol distributes in body water, so body size and composition directly affect BAC per drink:

• Lower body mass → less water for the same dose → higher BAC.
• Lower body water percentage (higher body fat) → higher BAC.

A 50kg patron drinking one standard drink will reach a meaningfully higher BAC than a 100kg patron drinking the same drink.

Sex

As covered in 5.2, females generally reach a higher BAC than males for the same intake due to lower body water, lower gastric ADH and higher body fat. This is an absorption-rate factor as well as a peak-BAC factor.

Genetics and Liver Enzyme Activity

Individual genetic variation in alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) activity means some people metabolise alcohol faster or slower than the average. Some East Asian populations carry an ALDH2 variant that causes acetaldehyde to accumulate, producing facial flushing and nausea after small amounts — a visible sign a duty manager may notice without the patron being 'drunk' in the SCAB sense.

Medication and Health

• Liver disease (e.g. cirrhosis, hepatitis) reduces metabolic capacity, so BAC stays higher for longer.
• Some medications inhibit enzymes or compete for metabolic pathways, slowing clearance. This is treated in more detail in 5.4.
• Fatigue and illness can amplify the visible signs even at a BAC the person would normally handle.

Type of Drink and Mixer

• Higher ABV drinks can irritate the stomach lining and the pyloric sphincter may close temporarily, slowing emptying — but in practice strong spirits consumed quickly still raise BAC fast.
• Mixer type matters: fizzy mixers speed absorption (above); juices or water slow it slightly; energy drinks can mask perceived intoxication (covered in 5.4).
• Warm drinks (mulled wine, hot toddies) are sometimes absorbed faster, though this is a smaller effect than food or carbonation.

Putting It Together: The 'Only Had Two' Patron

Consider a scenario the exam likes to test. A small (55kg) female patron arrives at 9pm having eaten nothing since noon. She orders two double gin and tonics and drinks both within twenty minutes. She tells staff 'I've only had two drinks.' Physiologically, her BAC may already be approaching or past the moderate-impairment band because:

• two doubles = four standard drinks,
• consumed rapidly,
• with carbonated tonic mixers,
• on an empty stomach,
• by a person with low body mass and female physiology.

The duty manager does not calculate this at the bar. The duty manager observes her signs — speech, coordination, behaviour, appearance — and intervenes on the basis of what they see. The physiology in this section exists so you understand why the signs can be pronounced despite a low drink count, and so you can explain it to a challenging patron or a junior server.

Link to Host Responsibility

Several of the factors above map directly onto host-responsibility strategies you will meet in Chapter 7:

• Food availability counters the empty-stomach effect.
• Promoting low-alcohol and non-alcoholic options reduces the dose per drink.
• Spacing drinks and offering water slows consumption and dilutes the dose.
• Avoiding high-alcohol promotions and drinking games addresses rapid consumption.

Understanding absorption turns these strategies from arbitrary rules into evidence-based prevention.