NEW YORK – A frothy beer or a glass of wine can enhance a meal and settle the mind. But what does alcohol do to the trillions of microbes living in your gut?

As with much of microbiome science, “there is a lot that 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 is clear that happy microbes are essential for proper digestion, immune function and intestinal health. And as scientists explore how drinking may influence your gut, they are learning that overdoing it could 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 regularly and heavily, said Dr Cynthia Hsu, a gastroenterologist at the University of California, San Diego.

A handful of studies, for instance, has 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 guts.

This is called dysbiosis, and it is generally associated with greater inflammation and disease compared with having a healthier microbiome, said Dr Hsu.

Dr Leggio said that heavy drinkers with dysbiosis can also have “leakier”, or more permeable, intestinal linings.

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 added.

When the gut lining breaks down, said Dr Hsu, bacteria and toxins can escape into the bloodstream and flow to the liver, where they can cause liver inflammation and damage.

Preliminary research suggests that an unhealthy gut might 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 alcohol-use disorder.

Those who reported...