A sparkling beer or glass of wine can enhance a meal and calm the mind. But what does alcohol do to the trillions of microbes that live in your gut?
As with much of microbiome science, “there’s a lot we don’t know,” said Dr. Lorenzo Leggio, a physician-scientist who studies alcohol use and addiction at the National Institutes of Health.
That said, it’s clear that happy microbes are essential for proper digestion, immune function, and gut health. And as scientists begin to investigate how booze can affect your gut, they’re learning that going overboard could have some nasty consequences.
How does heavy drinking affect your microbiome?
Most of the available research on alcohol and the microbiome has focused on regular and heavy drinkers, said Dr. Cynthia Hsu, a gastroenterologist at the University of California, San Diego.
A handful of studies, for example, have found that people with alcohol use disorder (inability to control or stop problem drinking) often have an imbalance of “good” and “bad” bacteria in their guts. This is called dysbiosis and is generally associated with more inflammation and disease compared to having a healthier microbiome, Dr. Hsu said.
Heavy drinkers with dysbiosis may also have a “leaky” or more permeable intestinal lining, Dr. Leggio said. A healthy gut lining acts as a barrier between the inside of the gut — filled with microbes, food and potentially harmful toxins — and the rest of the body, he said.
When the gut lining breaks down, bacteria and toxins can escape into the bloodstream and flow to the liver, Dr. Hsu added, where they can cause inflammation and liver damage.
Preliminary research suggests that an unhealthy gut may even contribute to alcohol cravings, said Dr. Jasmohan Bajaj, a hepatologist at Virginia Commonwealth University and the Richmond VA Medical Center.
In a 2023 study, for example, researchers looked at the microbiomes of 71 people aged 18 to 25 who did not have an alcohol use disorder. Those who reported more frequent binge drinking (defined as four or more drinks within about two hours for women or five or more drinks for men) had microbiome changes associated with greater alcohol cravings. This study also added to previous research that found that heavy alcohol consumption was associated with greater markers of inflammation in the blood.
However, none of these studies have proven that alcohol causes dysbiosis in humans. The link is clearer in animal studies, but in human studies, it’s harder for researchers to control for factors like diet and other health conditions.
What about those who drink less?
Federal guidelines define moderate drinking as no more than two drinks per day for men or one drink per day for women. There is very little research on how this amount of alcohol consumption affects your gut microbiome, said Jennifer Barb, a clinical bioinformatics scientist at the National Institutes of Health.
The scientists found that compared to those who don’t drink at all, people who drink at low to moderate levels have more diverse gut microbiomes—a trait generally associated with a healthy gut. This could be attributed to other dietary or lifestyle factors, or it could be that something in the alcoholic beverages can benefit the microbiome — though it’s probably not the ethanol, Dr. Barb said.
In a 2020 study of 916 women in Britain who consumed two or fewer drinks a day, for example, researchers found that those who drank red wine — or to a lesser extent white wine — had greater gut microbial diversity than non-drinkers. No such link was found with beer or liquor. The researchers hypothesized that polyphenols, compounds found in grape skins that are found in high concentrations in red wines, might explain their results.
But you don’t need alcohol to find polyphenols, said John Cryan, a neuroscientist who studies the microbiome at University College Cork in Ireland—they’re also in grapes and most other fruits and vegetables, as well as many herbs, coffee and tea. .
In general, eating a variety of plant-based and fermented foods such as yogurt, kombucha, and kimchi can also improve microbiome diversity.
Can cutting out alcohol improve your gut health?
Researchers looked at the microbiomes of people treated for alcohol use disorder and found that within two to three weeks after people stopped drinking, their gut microbes began to show signs of recovery, Dr. Barb said, and his mucosal their intestines became less “leaky”. But, he added, people who receive alcohol use disorder treatment usually also start eating healthier and sleeping better, which can improve gut health as well.
It’s not clear how — or even if — stopping or cutting down on alcohol might affect the microbiomes of moderate drinkers, Dr. Leggio said. But we do know that alcohol can cause acid reflux, stomach inflammation and gastrointestinal bleeding, he added, and can increase the risk of several types of cancer, including those of the esophagus, colon and rectum.
So “there’s no question,” Dr. Leggio said, that drinking less is a worthwhile endeavor for your health.
