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Have you ever noticed a change in your digestion after you’ve had a couple drinks? Maybe a few glasses of wine don’t affect you, but beer does, or vice versa. Just as many of us are still figuring out our own relationship with alcohol, scientists are beginning to explore the connection between consuming alcohol and the bacteria living in our gut microbiome.

“Individuals with an alcohol use disorder (inability to control or cease problematic drinking habits) have been found to have an imbalance of good and bad bacteria in their gut, also known as dysbiosis.”

While this is still a new field of study, most of the research on alcohol’s effect on the gut has focused on people who drink regularly and heavily, said Dr. Cynthia Hsu, a gastroenterologist at the University of California, San Diego. Studies have shown that individuals with an alcohol use disorder (inability to control or cease problematic drinking habits) have been found to have an imbalance of good and bad bacteria in their gut, also known as dysbiosis. Dysbiosis has been associated with greater inflammation and disease as well as “leakier” or permeable intestinal linings compared to those with a more balanced gut microbiome. A healthy gut lining acts as a barrier between the interior of the intestine, which is full of microbes, food and potentially harmful toxins, and the rest of the body, says Dr. Lorenzo Leggio, a physician-scientist who studies alcohol use and addiction at the National Institutes of Health. Dr. Hsu added that when the permeability of the gut lining is compromised, toxins can escape into the bloodstream and flow to the liver and other organs where they can cause inflammation and damage. In another study from 2023, researchers looked at the microbiome of 71 people ages 18 to 25 without a diagnosis of an alcohol use disorder. Those who reported more frequent binge drinking (four or more drinks within two hours for women or five or more drinks for men) showed microbiome changes that correlated with greater alcohol cravings which added to previous research showing that binge drinking was associated with greater blood markers of inflammation.

“People who drink low-to-moderate levels tend to have more diverse gut microbiomes – a characteristic generally associated with a healthier gut.”

For those who like to have a glass of wine with dinner or a few drinks with friends on the weekend, there is little research on how low-to-moderate drinking (two drinks per day for men and one for women) affects the gut microbiome, says Jennifer Barb, a clinical bioinformatics scientist at the National Institutes of Health. A Nature article published in 2020 found that compared with those who are completely abstinent from consuming alcohol, people who drink low-to-moderate levels tend to have more diverse gut microbiomes – a characteristic generally associated with a healthier gut. Dr. Barb says this is unlikely from the ethanol but can more likely be attributed to some ingredient or compound in alcoholic beverages or other diet or lifestyle factors.

“There is extensive research on the benefits of polyphenols due to their role in promoting the growth of beneficial bacteria in the gut microbiome…”

In a 2020 study observing 916 women in Britain who drank two or fewer alcoholic beverages per day, researchers found that those who drank wine – more so with red wine – had an increased gut microbial diversity compared with those who did not. Considering this association was not found with beer or liquor, the researchers hypothesized that polyphenols, compounds found in grape skins that are especially high in red wines, might be the answer. While more research still needs to be done to identify whether wine is the independent variable here, polyphenols can be found in most fruits and vegetables as well as many herbs, coffee and tea. There is extensive research on the benefits of polyphenols due to their role in promoting the growth of beneficial bacteria in the gut microbiome such as Lactobacillus and Bifidobacterium, which are two major beneficial probiotics that benefit overall human health.

“Since everyone’s relationship to drinking is different and everyone’s microbiomes are unique, it is important to consider how alcohol affects your own body and decide what is best for your overall health and well-being.”

So far, the link between alcohol and the microbiome has only been demonstrated in those who have an alcohol use disorder and in rodent studies. However, the results of low-to-moderate alcohol consumption and occasional binge drinking in human studies have not shown consistent results due to the difficulty of controlling variables like diet and lifestyle factors. Despite the evidence for a potential positive effect of moderate alcohol consumption on gut microbial diversity, and the potential role of wine polyphenols in this association, consumption of even moderate amounts of red wine cannot be recommended as a strategy to improve gut microbial function. Although more extensive research is needed to identify the effects of moderate levels of alcohol on the gut microbiome specifically, it is well known that high alcohol consumption can cause several negative symptoms to overall health depending on addiction history and current medical conditions. Since everyone’s relationship to drinking is different and everyone’s microbiomes are unique, it is important to consider how alcohol affects your own body and decide what is best for your overall health and well-being.