Grabbing a drink is an easy go-to activity when you’re making plans to catch up with a friend or getting together with colleagues after work. But drinking too much booze can come at a cost.
Researchers are beginning to unravel the many effects alcohol can have on the gut.
“Not only can alcohol by itself cause alcohol-associated diseases, it can also decrease the resiliency of the body to a whole host of problems,” Ali Keshavarzian, MD, director of the RUSH Center for Integrated Microbiome and Chronobiology Research in Chicago.
Here are five things you should know about how alcohol affects the gut and who is at higher risk for alcohol having a bigger impact on their gastrointestinal health.
1. It Encourages More Growth of Pro-Inflammatory Gut Bacteria
The biggest impact alcohol has on the gut is disrupting the balance of bacteria that make up the gut microbiome, says Dr. Keshavarzian.
Thousands of different types of bacteria, viruses, and fungi make up the gut microbiome. Most are beneficial and have a symbiotic relationship with the body, meaning both the microbe and the body benefit from each other. But some are potentially pathogenic, meaning they can cause disruptions in the body.
According to Cynthia Hsu, MD, PhD, an assistant professor in the division of gastroenterology at the University of California San Diego, when a person drinks large amounts of alcohol, the gut microbiome can change, favoring more potentially pathogenic microbes and killing off beneficial ones.
The Centers for Disease Control and Prevention (CDC) provide criteria for what constitutes heavy drinking based on the sex a person was assigned at birth. In general, eight or more alcoholic drinks per week constitutes heavy drinking for women, and 15 or more per week is considered heavy drinking for men, but alcohol affects different people in different ways, so fewer weekly drinks may be considered heavy drinking for some people.
“Unhealthy alcohol consumption can have a deleterious effect on the body through the gut by causing inflammation not only in the gut, but systemically,” Keshavarzian says.
A paper published in the International Journal of Environmental Research and Public Health noted pro-inflammatory gut bacteria can create inflammation in other parts of the body, which has been linked to obesity, Type 2 diabetes, and hardening of the arteries. Imbalanced gut bacteria have also been linked to mental health conditions such as depression.
According to a literature review published in the Journal of Gastroenterology and Hepatology, drinking alcohol is associated with decreased amounts of nine key beneficial bacteria that form symbiotic relationships with other bacteria. At the same time, alcohol appears to increase pathogenic bacteria. While the dysbiosis — when bacteria in the gut is imbalanced, usually giving way to more disease-supporting bacteria than healthy bacteria — can be reversed if a person gives up alcohol, sustained alcohol use disorder (AUD) may cause irreversible damage to the gut microbiome, Dr. Hsu and the study’s authors say.
When alcohol is consumed in the form of wine, mead, or mixed drinks, that excess sugar can have a compounded effect on the gut, too.
Early studies conducted in mice, including those outlined in a meta-analysis published in Nutrients, have shown that regularly consuming excess sugar can throw off the balance of anti-inflammatory and proinflammatory bacteria in the gut, creating an environment that favors pro-inflammatory bacteria. A study on mice published in Cell found that consuming excess sugar, at least in mice, alters the gut microbiome in a way that sets off a chain reaction that can lead to obesity and prediabetes.
2. It Can Cause Damage to the Lining of the Intestines
This build up of harmful, inflammatory gut bacteria caused by drinking can cause the lining in the intestines to thin.
“Those cells are there to act as a barrier to prevent more toxic substances from entering the bloodstream,” explains Hsu, who is also a staff physician at the San Diego VA Medical Center.
The intestines have a slimy mucus layer that acts as a barrier, letting nutrients through to the bloodstream and blocking toxins from the same pathways. Alcohol can make this thinner and looser, notes Keshavarzian.
He says to imagine the lining as a wall made of brick and mortar, where the bricks are the main structure and the mortar — essentially the glue between the bricks — keeps the barrier tightly sealed.
“The primary effect alcohol has is on the glue. It becomes loose and leaky,” Keshavarzian says.
When the gut becomes leaky, also called “leaky gut,” it’s easier for toxins to get into the bloodstream, which can have a negative effect on other organs.
3. It Can Damage the Liver
Alcohol damages the liver in several ways. The first is related to the intestinal layers that keep toxins out of the bloodstream.
“All of the blood that carries these toxins goes directly to the liver to be processed, so if there are more toxins in the blood, those toxins will hurt the liver,” Hsu says.
Imbalances in the gut microbiome can also cause similar disruptions in the liver.
In a review published in Nature Reviews Microbiology, Hsu and her colleague described how mounting research has found a link between imbalances in gut bacteria, including those caused by drinking alcohol, and how it can lead to harmful bacteria colonizing the liver and accelerating liver damage.
If a person drinks too much, they can develop a condition called alcohol-related liver disease (ARLD), which covers a number of different disorders, including fatty liver, alcoholic hepatitis, and cirrhosis.
Alcohol-related liver damage can be deadly.
A study published in JAMA Open Network, which included nearly 700,000 American adults 20 to 64 years, estimated that among adults 35 to 49 years, alcoholic liver disease was the second-most common way alcohol contributed to death, after overdoses on other substances.
4. It Can Cause Inflamed Stomach Lining
Binge drinking — having five or more drinks on one occasion, such as a night out, for men, and four for women, according to the CDC — can cause the mucus membrane lining in the stomach to become inflamed and thinned, causing a condition called reactive gastritis, per StatPearls.
Gastritis can be without symptoms, but it can also cause a gnawing or burning sensation in the upper abdomen that can get better or worse when you eat, nausea, stomach aches, and a feeling of fullness in your upper abdomen after you eat, according to the Mayo Clinic.
“Certainly heavy alcohol use can cause inflammation in the stomach and can irritate the esophagus and cause esophagitis,” Hsu says.
5. Even Small Amounts of Alcohol Can Have an Impact
According to Keshavarzian, there isn’t one magic dose of alcohol that affects the gut. It depends on a lot of factors, including the sex someone was assigned at birth.
People who were assigned female at birth have significantly smaller amounts of an enzyme in the stomach that digests alcohol, called alcohol dehydrogenase, he explains.
That’s why the CDC has different recommendations for drinking alcohol based on biological sex — two drinks or less per day for men and one or less for women. According to the CDC, people should not drink more than this on the days they do drink, and shouldn’t see these guidelines as a go-ahead to drink every day.
For people with underlying conditions, such as fatty liver, even moderate amounts of alcohol can cause damage.
Nearly 1 in 4 American adults have nonalcoholic fatty liver disease, according to the National Institute of Health, which doctors are now starting to call metabolic dysfunction-associated fatty liver disease (MAFLD), a condition in which fat cells build up in the liver.
In another study led by Hsu, published in the journal Hepatology, even modest alcohol use significantly had an effect on the gut microbiome of people with MAFLD, to a point where the microbiome was similar to that of people with alcohol use disorder.
“When I looked at their gut microbiomes, there were pretty significant differences between people who didn’t drink at all and people who drank at low levels,” Hsu says. People in the study who consumed low levels of alcohol drank no more than the equivalent of 20 grams of alcohol, or about 1.5 drinks, per day.
For people without underlying conditions such as MAFLD, Hsu says the key to safe alcohol consumption is moderation — no more than one drink per day for women and two for men, according to the CDC.
