How Alcohol Affects Your Digestive System & Bowel Movements

Explore the science behind how alcohol consumption can disrupt your digestive process, leading to unusual changes in bowel movements.

By Vincent Ho, Western Sydney University

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As we enter the festive season it’s a good time to think about what all those celebratory alcoholic drinks can do to your gut.

Alcohol can interfere with the time it takes for food to go through your gut (also known as the “transit time”). In particular, it can affect the muscles of the stomach and the small bowel (also known as the small intestine).

So, how and why does alcohol make your poos goes weird? Here’s what you need to know.

Diarrhoea and the ‘transit time’

Alcohol’s effect on stomach transit time depends on the alcohol concentration.

In general, alcoholic beverages such as whisky and vodka with high alcohol concentrations (above 15%) slow down the movement of food in the stomach.

Beverages with comparatively low alcohol concentrations (such as wine and beer) speed up the movement of food in the stomach.

These changes in gut transit explain why some people can get a sensation of fullness and abdominal discomfort when they drink vodka or whisky.

How long someone has been drinking a lot of alcohol can affect small bowel transit.

We know from experiments with rats that chronic use of alcohol accelerates the transit of food through the stomach and small bowel.

This shortened transit time through the small bowel also happens when humans drink a lot of alcohol, and is linked to diarrhoea.

Alcohol can also reduce the absorption of carbohydrates, proteins and fats in the duodenum (the first part of the small bowel).

Alcohol can lead to reduced absorption of xylose (a type of sugar). This means diarrhoea is more likely to occur in drinkers who also consume a lot of sugary foods such as sweets and sweetened juices.

Chronic alcohol use is also linked to:

This means chronic alcohol use may lead to diarrhoea and loose stools.

How might a night of heavy drinking affect your poos?

When rats are exposed to high doses of alcohol over a short period of time, it results in small bowel transit delay.

This suggests acute alcohol intake (such as an episode of binge drinking) is more likely to lead to constipation than diarrhoea.

This is backed up by recent research studying the effects of alcohol in 507 university students.

These students had their stools collected and analysed, and were asked to fill out a stool form questionnaire known as the Bristol Stool Chart.

The research found a heavy drinking episode was associated with harder, firm bowel motions.

In particular, those who consumed more alcohol had more Type 1 stools, which are separate hard lumps that look or feel a bit like nuts.

The researchers believed this acute alcohol intake results in small bowel transit delay; the food stayed for longer in the intestines, meaning more water was absorbed from the stool back into the body. This led to drier, harder stools.

Interestingly, the researchers also found there was more of a type of bacteria known as “Actinobacteria” in heavy drinkers than in non-drinkers.

This suggests bacteria may have a role to play in stool consistency.

But binge drinking doesn’t always lead to constipation. Binge drinking in patients with irritable bowel syndrom (IBS), for example, clearly leads to diarrhoea, nausea and abdominal pain.

What can I do about all this?

If you’re suffering from unwanted bowel motion changes after drinking, the most effective way to address this is to limit your alcohol intake.

Some alcoholic beverages may affect your bowel motions more than others. If you notice a pattern of troubling poos after drinking certain drinks, it may be sensible to cut back on those beverages.

If you tend to get diarrhoea after drinking, avoid mixing alcohol with caffeinated drinks. Caffeine is known to stimulate contractions of the colon and so could worsen diarrhoea.

If constipation after drinking is the problem, then staying hydrated is important. Drinking plenty of water before drinking alcohol (and having water in between drinks and after the party is over) can help reduce dehydration and constipation.

You should also eat before drinking alcohol, particularly protein and fibre-rich foods.

Food in the stomach can slow the absorption of alcohol and may help protect against the negative effects of alcohol on the gut lining.

Is it anything to worry about?

Changes in bowel motions after drinking are usually short term and, for the most part, resolve themselves pretty efficiently.

But if symptoms such as diarrhoea persist beyond a couple of days after stopping alcohol, it may signify other concerning issues such as an underlying gut disorder like inflammatory bowel disease.

Researchers have also linked alcohol consumption to the development of irritable bowel syndrome.

If problems persist or if there are alarming symptoms such as blood in your stool, seek medical advice from a general practitioner.

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