Scientists have identified specific gut bacteria and biological pathways that cause alcohol to be produced inside the body in people with auto-brewery syndrome (ABS). This rare and frequently misunderstood condition causes individuals to experience intoxication even though they have not consumed alcohol. The research was conducted by a team at Mass General Brigham in collaboration with researchers from the University of California San Diego and was published on January 7 in Nature Microbiology.
Auto-brewery syndrome develops when certain microbes in the gut break down carbohydrates and convert them into ethanol (alcohol), which then enters the bloodstream. While normal digestion can create trace amounts of alcohol in anyone, people with ABS can produce levels high enough to cause noticeable intoxication. Although the condition is extremely rare, experts believe it is often missed because of limited awareness, difficulties with diagnosis, and social stigma.
Many people with ABS spend years without an accurate diagnosis. During that time, they may face social strain, medical complications, and even legal problems linked to unexplained intoxication. Confirming the condition is also challenging because the gold-standard diagnostic approach requires carefully supervised blood alcohol testing, which is not easily accessible in many settings.
To investigate the biological roots of the disorder, researchers studied 22 people diagnosed with ABS, along with 21 unaffected household partners and 22 healthy control participants. The team compared the makeup and activity of gut microbes across these groups to identify meaningful differences.
Laboratory testing showed that stool samples collected from patients during active ABS flare-ups produced far more ethanol than samples from household partners or healthy controls. This finding highlights the possibility of developing a stool-based test that could make diagnosing the condition easier and more reliable in the future.
Identifying the Microbes and Pathways Involved
Until now, scientists had limited information about which specific gut microbes (yeasts or bacteria) were responsible for auto-brewery syndrome. Detailed stool analysis pointed to several bacterial species as key contributors, including Escherichia coli and Klebsiella pneumoniae. During symptom flare-ups, some patients also showed much higher levels of enzymes involved in fermentation pathways compared to control participants. The researchers note that identifying the exact causative microbes in individual patients remains a complex and time-consuming task.
The research team also followed one patient whose symptoms improved after receiving a fecal microbiota transplantation when other treatments had not worked. Periods of relapse and recovery closely matched changes in specific bacterial strains and metabolic activity in the gut, offering additional biological evidence for the condition. After a second fecal transplant, using a different antibiotic pretreatment, the patient remained symptom-free for more than 16 months.
"Auto-brewery syndrome is a misunderstood condition with few tests and treatments. Our study demonstrates the potential for fecal transplantation," said co-senior author Elizabeth Hohmann, MD, of the Infectious Disease Division in the Mass General Brigham Department of Medicine. "More broadly, by determining the specific bacteria and microbial pathways responsible, our findings may lead the way toward easier diagnosis, better treatments, and an improved quality of life for individuals living with this rare condition."
