Gut bacteria sometimes get people drunk, leading to DUIs and liver disease

Imagine you're a police officer. You spot a car that's swerving all over the road. You pull the driver over and they're clearly intoxicated. With slurred speech, they swear that they haven't had a drop of alcohol all day. Would you believe them?

In 2024, a Belgian man was acquitted after he was cited three times for DUI within four years. Though his job at a brewery likely raised suspicions, he insisted that he hadn't been drinking. Three doctors confirmed that he suffered from a condition called auto-brewery syndrome and was unaware. People with this syndrome carry microbes in their intestines that produce abnormally high levels of alcohol when breaking down sugars and carbohydrates.

Though it's a rare condition, a woman was acquitted of her DUI charge in 2016 after doctors diagnosed her with the same syndrome. She had a blood alcohol level four times the legal limit.

I am a microbiologist who is intrigued by the roles the gut microbiome plays in human health. As the author of the book "Pleased to Meet Me: Genes, Germs, and the Curious Forces That Make Us Who We Are," I have done extensive research into how your microbiome affects your health, mood and behavior. It turns out the specific species of bacteria in your intestines at the root of auto-brewery syndrome may also cause fatty liver disease by producing high levels of alcohol.

Diseased liver, without drinking

The accumulation of excess fats in the liver can cause serious Health problems, including iNFLaMMAtion. This can lead to cirrhosis, or scarring, and liver cancer. Most people associate fatty liver disease with alcoholism. However, metabolic dysfunction-associated steatotic liver disease, or MASLD, arises without excessive alcohol intake. Formerly known as nonalcoholic fatty liver disease, this condition affects 80 million to 100 million Americans.

There appear to be multiple causes of MASLD, such as obesity, insulin resistance, high cholesterol and hepatitis C infection. Microbes may be another.

In a 2019 study, physicians identified a patient who was suffering from both auto-brewery syndrome and severe MASLD. When researchers examined stool samples from the patient, they found a species of bacteria called Klebsiella pneumoniae. This particular strain of K. pneumoniae was making between four and six times the quantity of alcohol that strains of the same bacteria make in healthy people. Examining a cohort of 43 other patients with MASLD, they discovered that 61% of participants possessed K. pneumoniae excreting unusually high amounts of alcohol. Among the 48 healthy people included as controls, only 6% had such bacteria.