When Gut Bacteria Make Alcohol Inside the Body

New microbiome research explains auto-brewery syndrome and points to practical diagnostic and treatment pathways.

Carefully designed microbiome profiling confirms that specific gut bacteria can ferment carbohydrates into clinically significant amounts of alcohol, validating auto-brewery syndrome and opening new directions for diagnosis, diet, and treatment.

Study Details

Auto-brewery syndrome, or ABS, describes a rare but disruptive condition in which people develop symptoms of alcohol intoxication without drinking alcohol. For years, many patients were dismissed or misdiagnosed, often labeled as covert drinkers. A new study published in Nature Microbiology examined 22 patients with confirmed ABS and provides the most rigorous biological explanation to date.

Researchers used deep metagenomic sequencing and fecal metabolomics to identify the microbes and metabolic pathways responsible for endogenous ethanol production in the gut. Importantly, patients were compared with healthy household members to reduce shared diet and environmental bias.

Methodology

Participants underwent supervised carbohydrate challenge testing using 75 to 100 grams of glucose, followed by serial blood alcohol measurements over six hours. Stool samples were analyzed using metagenomic sequencing to identify bacterial species and functional metabolic pathways. Fecal cultures were tested for ethanol production, and targeted antimicrobial experiments were used to determine whether bacteria or fungi were responsible.

This combined approach allowed researchers to link specific microbial strains, fermentation pathways, and measurable blood alcohol levels in real time.

Key Findings

• Gut bacteria, not fungi, were the primary source of alcohol production, overturning long-standing assumptions about Candida overgrowth

• Symptomatic patients reached mean blood alcohol levels of 136 mg/dL despite no alcohol intake

• Proteobacteria such as E coli and Klebsiella pneumoniae were enriched, alongside reduced microbial diversity

• Multiple fermentation pathways operated simultaneously, explaining why single-antibiotic treatments often fail

• Fecal acetate levels strongly correlated with blood alcohol levels, suggesting a self-sustaining metabolic loop

• One refractory patient achieved long-term remission after targeted antibiotics followed by fecal microbiota transplantation

Implications for Practice

For patients
This research provides validation. Individuals who experience intoxication after meals without drinking are not imagining symptoms or hiding behavior. Dietary carbohydrate restriction remains a cornerstone of symptom control, and newer microbiome-based diagnostics can offer objective confirmation.

For clinicians
ABS should be considered in patients with unexplained intoxication, positive breathalyzer tests without alcohol intake, or atypical liver disease progression. Diagnostic protocols must extend to at least six hours after carbohydrate challenge to capture delayed ethanol peaks. Treatment strategies should shift away from antifungal monotherapy toward bacteria-focused approaches, and in refractory cases, fecal microbiota transplantation may be appropriate with long-term follow-up.

Beyond ABS, these findings raise broader questions about whether chronic low-level microbial alcohol production could contribute to metabolic liver disease even in people who never drink.