How does alcohol affect the microbiome?

As a researcher who studies diet and the microbiome, I often hear questions about how everyday choices impact the body.

One area that people are especially curious about is alcohol. How much is safe to drink? Can drinking harm the microbiome? How can I repair my microbiome if I drink too much?

Below, I answer common questions about how drinking alcohol can affect the body’s microbiome and what it means for our overall health.

What is the microbiome? 

The microbiome is our body’s non-human inhabitants, such as bacteria, viruses and fungi. Humans have an oral microbiome and a gut microbiome.

When we are talking about the gut microbiome, we're mostly talking about our bowel: our colon all the way down to our rectum.

Normally, the gut microbiome has a healthy balance of bacteria. These bacteria help our bodies by:

• supporting our immune system 
• supporting our metabolism
• regulating inflammation
• working with the liver to defend against toxins
• helping to prevent chronic and infectious diseases 
  

How does drinking alcohol affect the body’s microbiome?

Diet, or what we ingest, has a huge impact on the microbiome. When we drink alcohol, it impacts everything from the oral microbiome all the way through the digestive system. It also involves a lot of other organs along the way.

Here are three things that can happen in the gut microbiome when we drink alcohol.

Alcohol changes the balance of bacteria in the gut microbiome. 

First, alcohol can change the composition, or balance, of the gut microbiome. This can cause the gut microbiome to go from a state of homeostasis where everything is happy and calm into a state of dysbiosis where things start to go out of whack.

Metabolites can harm the microbiome

The gut microbiome works to metabolize the different components of alcoholic drinks. In doing so, it creates products, called metabolites, that are used to signal between the gut microbiome, liver and blood. Some of the metabolites that are created when your body breaks down alcohol can be toxic.

Leaky gut 

There is a protective mucus layer on the intestinal lining of our gut. When our gut microbiome starts to get out of balance, it begins to eat at the protective layers between the gut, the rest of our body and our circulating blood. This causes a change in gut integrity, or a leaky gut.

Does the microbiome play a role in alcohol’s link to cancer?

Alcoholic drinks contain ethanol. Ethanol is considered a carcinogen. It's a toxin that causes DNA damage and ramps up reactive oxygen species, which are mechanisms associated with cancer. 

If you have a leaky gut, toxins from metabolizing alcohol can get into the bloodstream and cause things to go awry beyond the gut microbiome, usually starting with the liver.  

However, these toxins can also increase cancer risk outside the gastrointestinal system. Cancers that are linked to drinking alcohol include:

• esophageal cancer
• colorectal cancer
• stomach cancer
• liver cancer
• oral cancer
• breast cancer  

The gut microbiome is really opening up how we understand this problem. Alcohol affects both the oral microbes and gut microbes which play important roles in cancer risk.

How else can alcohol impact the microbiome?

The gut microbiome is a big part of how our body metabolizes what we eat, what we drink and the medications we take. Working in a delicate balance with the liver, it helps to control the amount of ethanol or toxins that impact our health more broadly. 

Alcohol can cause gastritis. The enzymes in the stomach lining can be overwhelmed, and the lining can start to break down. There’s a reason why drinking too much alcohol makes us sick to our stomach and can lead to vomiting and diarrhea: you’re sort of overwhelming the system.  

How should we proceed?

Going forward, it is helpful to know about alcohol dosage and your personal alcohol sensitivity.

Understand alcohol serving sizes

MD Anderson says that for cancer prevention, it is best not to drink alcohol. However, for those that choose to drink, men should limit themselves to two drinks per day, while women should limit themselves to one drink a day. 

Some people are surprised to learn that a standard drink looks different depending on the type of alcohol. The Centers for Disease Control and Prevention (CDC) writes that a standard drink has 0.6 ounces of pure alcohol. This is the amount of pure alcohol that is usually in 12 ounces of beer, 5 ounces of wine or 1.5 ounces of 80-proof distilled spirits or liquor.  

There may be a limited or acceptable amount of alcohol that a healthy body, with everything working in perfect harmony, can get out of the system appropriately. However, everyone is different, and things can go wrong at different places along the way.

Know why people respond differently to alcohol 

People break down alcohol differently. A well-documented example of this is the difference in how men and women break down alcohol. 

I didn’t understand the recommendations that suggest women drink half as much alcohol as men until I went to graduate school. I thought it was all about size. I thought, ‘I’m a 5’8 woman, why is my recommendation different than a 5’8 man?’ 

I later learned it doesn't have to do with size; it has to do with metabolic function. People's personal biological and genetic sensitivity to alcohol, and how well they break down alcohol into its toxic and nontoxic components, is based on how much of an enzyme called alcohol dehydrogenase (ADH) they have. 

ADH levels are different in men and women, as well as in people of different racial and ethnic backgrounds. This is determined by our genetics.

Although we give recommendations for alcohol consumption, they might not apply to everyone. Some people may be so sensitive to alcohol that they can’t tolerate that amount. That's why MD Anderson and other organizations have said there’s no safe amount of alcohol for cancer risk. At the end of the day, we don't know what your specific situation is.  

Can your microbiome be repaired?

When it comes to alcohol and other nutritional components, if you're having a bad week, you can put your microbiome in quite a bad state. 

The good news is that, typically, if you make an effort to go back to healthier ways, the microbiome will go back to the same state it was in before.

Something interesting I’ve seen with diet and alcohol is that the decline happens faster than the repair. For example, maybe it takes eight weeks to build this really healthy microbiome, but in less than two weeks, you can turn that around in the wrong direction.  

What is important is how far down you go and how long you stay there. If you put your microbiome in a state of stress for an extended period of time, it's actually pretty selfish and it will put its own needs over yours. That's why it starts to eat things like the mucus layer. It doesn't want to starve and die, so it starts taking from you. That's when things start to really go in the wrong direction. 

The gut microbiome is really important for immunity. People joke “I'm going to drink alcohol and kill all the bad stuff,” but that's not how it works. You want your gut microbiome to be really healthy to fight infections; it's a critical part of our overall immune system. It is also really important for regulating inflammation not only in the gut, but throughout the whole body. Infection, poor eating habits or smoking can create pro-inflammatory conditions. When you drink alcohol on top of that, it's like adding fuel to the fire. The microbiome can't bounce back to take care of you. It’s our friend until it's in trouble, and then it is not our friend.

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