Researchers have found that certain gut microbes can transform food into alcohol at levels high enough to cause intoxication, in rare cases where the digestive system acts as an internal brewery.
A very small number of people can naturally experience symptoms of intoxication despite not consuming any alcohol. This condition comes with many frustrating complications, as patients, family, and friends often have trouble understanding the disease; even doctors have struggled to explain its origins. Some patients have even faced legal consequences for driving under the influence without ever touching a drink.
The findings are detailed in a new study that appeared in Nature Microbiology, led by researchers at Mass General Brigham and the University of California San Diego.
A Rare Condition With Serious Consequences
Auto-brewery syndrome occurs when gut microbes ferment carbohydrates from food into ethanol. Most people only produce trace amounts of alcohol during digestion, but people with this syndrome can naturally produce alcohol levels high enough to be considered legally intoxicated.
The condition is hard to diagnose. The most reliable test involves giving patients carbohydrates under supervision and measuring their blood alcohol levels over time, but this approach is relatively inefficient. Many patients have spent years searching for an explanation for their symptoms.
“Auto-brewery syndrome is a misunderstood condition with few tests and treatments,” said Elizabeth Hohmann, an infectious disease physician at Mass General Brigham and a co-senior author of the study.
Tracking Alcohol Production
Researchers studied 22 people diagnosed with auto-brewery syndrome to investigate the biological basis of the disorder. The study also included 21 unaffected household partners and 22 healthy control participants. Including household partners in this study allowed the team to account for shared diets and other environmental influences.
The team collected stool samples during periods when patients were experiencing symptoms of intoxication and measured the ethanol in each sample. The results showed clear differences between groups.
Samples from patients with auto-brewery syndrome produced significantly more ethanol than those from household partners or healthy control participants. In some cases, the amount of ethanol was enough to explain the levels of intoxication observed in patients.
This evidence suggests that stool-based fermentation tests could eventually provide a simpler, more accessible way to diagnose the condition.
Identifying the Microbial Culprits
The study also goes beyond earlier theories about the origins of auto-brewery syndrome. Many of these focused on overactive yeast growth within the system. However, detailed microbial and metabolic analyses identified other bacterial species as the main contributors to this condition.
During periods of intoxication, patients showed increased levels of enzymes involved in fermentation, directly linking changes in the gut microbiome to ethanol production. The researchers note that the condition does not result from a single pathogen but appears to be caused by disruptions in the gut ecosystem that promote fermentation.
Identifying the specific microbes responsible for each patient’s intoxication remains complicated and time-consuming. Still, the alignment of microbial and metabolic evidence supports a biological explanation for the syndrome.
Fecal Transplantation
The team focused on one patient after standard treatments proved ineffective. The patient received a fecal microbiota transplant, a procedure that aims to reset the gut ecosystem using donor microbes.
After the first transplant, the patient’s symptoms improved, but only temporarily. Both relapse and recovery were associated with changes in bacterial strains and gut metabolic activity. A second transplant used a different antibiotic pretreatment, which led to the patient staying symptom-free for more than 16 months.
A Path Forward
Although this result is based on a single patient, it provides a long-term view of how changes in the gut microbiome can influence clinical outcomes.
“Our study demonstrates the potential for fecal transplantation,” Hohmann said, adding that identifying responsible microbes could lead to better diagnostic tools and targeted therapies.
The team’s findings help provide context to a long-misunderstood condition. For patients suffering from auto-brewery syndrome, this new research can provide a possible path forward with legitimate biological evidence and a credible diagnosis.
Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds a Master of Business Administration, a Bachelor of Science in Business Administration, and a Data Analytics certification. His work combines analytical training with a focus on emerging science, aerospace, and astronomical research.