How does alcohol affect your gut health?
A frothy beer or glass of wine can enhance the 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 abuse and addiction at the National Institutes of Health.
However, it is clear that a happy microbiome is essential for healthy digestion, immune function, and gut health. As scientists begin to explore how drinking affects your gut, they’re learning that drinking too much can have some unhappy consequences.
How does heavy drinking affect your microbiome?
Most of the available research on alcohol and the microbiome has focused on people who drink alcohol regularly and heavily, said Dr. Cynthia Hsu, a gastroenterologist at the University of California, San Diego.
For example, a group of studies have found that people with alcohol use disorder (the inability to control or stop drinking) often have an imbalance of “good” and “bad” bacteria in their gut. This is called dysbacteriosis, and is generally associated with increased inflammation and disease compared to having a healthier microbiome, Dr. Hsu said.
Heavy drinkers with dysbiosis can also have “leakier” or more permeable intestinal linings, Dr. Leggio said. A healthy gut lining acts as a barrier between the interior of the intestine — full of microbes, food and potentially harmful toxins — and the rest of the body, he said.
Dr. Hsu added that when the intestinal lining breaks down, bacteria and toxins can seep into the bloodstream and flow to the liver, where they can cause liver inflammation and damage.
Preliminary research suggests that an unhealthy gut may contribute to alcohol cravings, said Dr. Jasmohan Bajaj, a hepatologist at Virginia Commonwealth University and Richmond VA Medical Center.
In a 2023 study, for example, researchers looked at the microbiota of 71 people ages 18 to 25 who did not have alcohol use disorder. Those who reported frequent binge drinking (defined as four or more drinks in about two hours for women, or five or more drinks for men) had changes in their microbiome that were associated with increased alcohol cravings. This study also added to previous research that found that heavy drinking is associated with increased markers of inflammation in the blood.
However, none of these studies have proven that alcohol causes dysbacteriosis in humans. The link is clearer in animal studies, but in human studies, it is difficult for researchers to control factors such as 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’s very little research on how this amount of alcohol consumption affects the gut microbiome, said Jennifer Barb, a clinical bioinformatician at the National Institutes of Health.
Scientists have found that compared to those who don’t drink at all, people who drink at low to moderate levels have a more diverse gut microbiome — a characteristic generally associated with a healthy gut. This could be attributable to other diet or lifestyle factors, or there may be something in alcoholic beverages that may benefit the microbiome — although it’s likely not ethanol, Dr. Barb said.
In a 2020 study of 916 women in Britain who drank 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 those who did not. No such association was found with beer or alcoholic beverages. The researchers hypothesized that polyphenols, compounds found in grape skins and found in high concentrations in red wine, might explain their results.
You don’t need alcohol to find polyphenols, they’re also found in grapes and most other fruits and vegetables, as well as many herbs, coffee and tea, said John Cryan, a neuroscientist who studies the microbiome at University College Cork in Ireland. .
In general, consuming a variety of plant-based foods and fermented foods such as yogurt, kombucha, and kimchi can improve microbiome diversity as well.
Can reducing your alcohol intake improve your gut health?
Researchers looked at the microbiome 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 their gut linings became less “leaky.” But she added that people who are treated for alcohol use disorder usually start eating healthier and sleeping better, which may improve gut health as well.
It’s not clear how — or even whether — quitting or cutting back on alcohol might affect the microbiome of moderate drinkers, Dr. Leggio said. He added that we know that alcohol can cause acid reflux, inflammation of the stomach lining, and gastrointestinal bleeding, and can increase the risk of several types of cancer, including esophageal, colon, and rectal cancer.
So, Dr. Leggio said, “there’s absolutely no doubt” that drinking less is a beneficial endeavor for your health.