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How Your Body Breaks Down Alcohol

Breaking down alcohol: alcohol 101, Part 1


This is Part 1 in what will be a three-part series on everything you need to know about alcohol. This first part explains how your body processes alcohol. The second and third parts will go into the effects of alcohol on your body and what you can do to help your body out when you’re drinking.


How does your body process the alcohol you ingest? Note that when we say “alcohol” in this post, we’re referring to the molecule ethanol (also called ethyl alcohol, if you’re not into the whole brevity thing). Let’s start with the basic biochemistry.

The breakdown of alcohol in your body occurs in two stages:

These two chemical reactions are mediated by two different and specialized enzymes that break down alcohol (enzymes are proteins that catalyze chemical reactions):

  1. The first reaction is mediated by an enzyme called alcohol dehydrogenase. This enzyme removes a pair of electrons along with two hydrogen atoms from alcohol to make acetaldehyde (On paper this is chemically the same as removing hydrogen gas, hence the old-timey name de-hydrogen-ase). 
  2. The second reaction is mediated by an enzyme called – you guessed it – acetaldehyde dehydrogenase. This enzyme removes another pair of electrons (and a hydrogen atom) to allow water to bond with the acetaldehyde (in the form of a hydroxy group) to make acetate.

At this point we are left with acetate, a harmless molecule – essentially vinegar. And this is as far as we need to go for the purposes of understanding alcohol metabolism from a biochemical standpoint.

How does the body metabolize alcohol

Your liver – the major site of alcohol metabolism

Where does this biochemistry take place? The vast majority of the alcohol you drink is processed by your liver after it is absorbed into your bloodstream from your gut.

The basic path of alcohol through the body is:

  1. Ingestion in your mouth
  2. Into your stomach, where about 20% of the alcohol is absorbed directly through the stomach lining. The more food you have in your stomach, the slower the alcohol is absorbed here, and the longer it takes to move into your intestines.
  3. Into your small and large intestines (for simplicity, we’ll call this your “gut”), where most of the rest of the alcohol is absorbed through the intestinal lining. A small amount of the alcohol is directly metabolized here by the microbes living in your gut (which we’ll discuss in more detail in the next section).
  4. Into your bloodstream, where it circulates throughout the entire body, including your brain, muscles, etc., creating the various effects you feel from drinking (e.g. intoxication, hunger, etc. – more on this in part 2).
  5. Into your liver, where the two chemical reactions discussed above take place. Your liver produces sufficient amounts of both enzymes (alcohol dehydrogenase and acetaldehyde dehydrogenase) to quickly process the alcohol to acetaldehyde, and then to acetate.

Importantly, almost none of the intermediate acetaldehyde escapes the liver; nearly all of it is immediately processed to acetate via the liver pathway.* However, the same is not true in the gut.

*It’s worth noting that this is different for people with an acetaldehyde dehydrogenase deficiency, a genetic condition experienced by approximately 8% of the global population (citation).

Your gut – the minor site of alcohol metabolism

Interestingly, a small amount of the alcohol you drink is metabolized directly in the gut itself, rather than the liver (citation). This happens before the alcohol gets absorbed into the bloodstream, and is the result of biochemical activity in a surprising place: your gut microbiome. 

The microbes in your gut (collectively known as your gut microbiome) also produce alcohol dehydrogenase enzymes, converting alcohol into acetaldehyde (citation). 

However, unlike in your liver, these microbes only do the first step of the process. They do not subsequently convert acetaldehyde to acetate. And without that second reaction, acetaldehyde produced in your gut starts to accumulate. As such, while only a relatively small amount of alcohol is processed this way, it results in the largest amount of persistent acetaldehyde creation in your body (citation).

In fact, so much acetaldehyde is produced by your microbiome that gut acetaldehyde concentrations can reach levels 5-10x higher than in the rest of your body. At this point, all that acetaldehyde is absorbed out of the gut into the bloodstream.

This isn’t without consequence. Acetaldehyde is a very nasty molecule that wreaks havoc on your body and is responsible for a large share of the misery you might feel the day after drinking. We’ll go into more detail about this in a future post, but it is important to note that this is a major difference between the liver and the gut pathways for alcohol metabolism, and it’s at the heart of why ZBiotics’ first product exists. You can read more about acetaldehyde and the science underlying that first product here.

In Summary

So to recap, your body processes alcohol in two stages: (1) from alcohol to acetaldehyde; and (2) from acetaldehyde to acetate. In terms of alcohol metabolism your liver does most of the work and efficiently converts nearly all the alcohol it encounters to the innocuous acetate. Your gut (and the microbes in your gut) process a small amount of alcohol before it gets absorbed, but the majority of that alcohol is converted to toxic acetaldehyde, not acetate.

Up next is part 2 of the series, where we discuss the effects alcohol has on your body, and part 3, where we outline best habits and practices while drinking to help your body as it’s processing alcohol.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice.