A sparkling beer or glass of wine can enhance a meal and calm the mind. But what does alcohol do for the trillions of microbes that live in your gut?
As with much of microbiome science, “there’s a lot we don’t know,” says Lorenzo Leggio, a physician scientist who studies alcohol use and addiction at the National Institutes of Health.
That said, it’s clear that healthy microbes are essential for proper digestion, immune function, and gut health. And as scientists begin to explore how drinking alcohol can influence your gut, they’re discovering that overdoing it can have some unfortunate consequences.
HOW DOES EXCESSIVE ALCOHOL CONSUMPTION AFFECT YOUR MICROBIOME?
Most of the available research on alcohol and the microbiome has focused on people who drink regularly and in large quantities, says Cynthia Hsu, a gastroenterologist at the University of California, San Diego.
Some studies, for example, have found that people with alcohol use disorder (the inability to control or stop problematic drinking) often have an imbalance of “good” and “bad” bacteria in their intestines. This is called dysbiosis and is often associated with greater inflammation and disease compared to a healthier microbiome, says Hsu.
People who drink excessively and have dysbiosis may also have more “leaky” or leaky intestinal linings, says Leggio. A healthy intestinal lining acts as a barrier between the inside of the intestine — full of potentially harmful microbes, foods and toxins — and the rest of the body, he says.
When the intestinal lining breaks down, bacteria and toxins can escape into the bloodstream and flow to the liver, where they can cause inflammation and damage, adds Hsu.
Preliminary research suggests that an unhealthy gut may even contribute to alcohol cravings, says Jasmohan Bajaj, a hepatologist at the University of Virginia and the Richmond VA Medical Center.
In a 2023 study, for example, researchers analyzed the microbiomes of 71 people ages 18 to 25 who did not have alcohol use disorder. Those who reported binge drinking more frequently (defined as four or more drinks in about two hours for women, or five or more drinks for men) had changes in the microbiome that correlated with greater alcohol cravings. This study also added to previous research that found excessive alcohol consumption was associated with higher blood markers of inflammation.
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 alcohol consumption 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 the gut microbiome, says Jennifer Barb, a clinical bioinformatics scientist at the National Institutes of Health.
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 alcoholic beverages could benefit the microbiome — although it’s probably not the ethanol, says Barb.
In a 2020 study of 916 women in Britain who consumed two or fewer drinks per day, for example, researchers found that those who drank red wine — or to a lesser extent, white wine — had greater gut microbial diversity than those who didn’t drink. No such link has been found with beer or spirits. The researchers hypothesized that polyphenols, compounds found in grape skins in high concentrations in red wines, could explain their results.
But you don’t need alcohol to find polyphenols, says John Cryan, a neuroscientist who studies the microbiome at University College Cork in Ireland — they’re also present in grapes and most other fruits and vegetables, as well as many herbs, coffee and tea. .
In general, consuming a variety of plant-based foods and fermented foods like yogurt, kombucha, and kimchi can also improve microbiome diversity.
CAN REDUCING ALCOHOL CONSUMPTION IMPROVE YOUR GUT HEALTH?
Researchers analyzed the microbiomes of people who were 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, says Barb, and their intestinal linings became less “leaky”. But, she adds, people who are treated for alcohol use disorder also often start eating healthier and sleeping better, which can also improve gut health.
It’s not clear how — or even if — stopping or reducing alcohol consumption might influence the microbiomes of moderate drinkers, says Leggio. But we know that alcohol can cause acid reflux, inflammation of the stomach lining 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 “absolutely no doubt,” says Leggio, that drinking less is a worthwhile endeavor for your health.