Auto-Brewery Syndrome: When Your Gut Produces its Own Alcohol

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In 2013, a 61-year-old man arrived at the emergency room of a Texas hospital with a blood alcohol level of 0.37 g/dL. He claimed he had not been drinking. The medical staff did not believe him, since 0.37 g/dL is equivalent to consuming, in one go, nearly ten standard pints.

When Dr. Barbara Cordell’s team hospitalized him for twenty-four hours in a controlled room, with no access to any type of alcohol, his blood ethanol level rose again after each meal.

The diagnosis came after analyzing his stool, as his large intestine harbored a massive concentration of Saccharomyces cerevisiae, the same yeast that ferments beer (Cordell and McCarthy, 2013).

That case documented for the first time with rigor what is known as “auto-brewery syndrome” or “automatic fermentation” and demonstrated that the human body can, under certain conditions, become an ethanol bioreactor.

What is auto-brewery syndrome?

Auto-brewery syndrome is a medical disorder characterized by the endogenous production of ethanol from the fermentation of carbohydrates in the gastrointestinal tract.

The responsible yeasts—mainly Saccharomyces cerevisiae, although Candida albicans, Candida glabrata, and other species have also been identified—metabolize ingested sugars and produce ethyl alcohol in sufficient quantities to raise blood alcohol levels without any external consumption of alcoholic beverages.

The biochemical reaction involved is exactly the same as that occurring in any brewery fermenter:

C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂

One molecule of glucose breaks down into two of ethanol and two of carbon dioxide. The difference between an industrial fermenter and the large intestine is not in the chemistry, but in the control.

The brewer manages temperature, substrate concentration, strain, and available oxygen. In the intestine, the process occurs within a complex, dynamic, and difficult-to-regulate microbial ecosystem.

What is the difference with conventional intoxication?

In ordinary intoxication, ethanol enters orally, is absorbed in the small intestine, and the liver processes it through the enzyme alcohol dehydrogenase (ADH).

In auto-brewery syndrome, ethanol is produced directly in the large intestine, where absorption is slower but continuous.

The liver receives a sustained flow of ethanol, not a single bolus, which can mask initial symptoms and complicate diagnosis.

How do yeasts ferment in the intestine?

The large intestine of an adult human contains between 10¹¹ and 10¹² microorganisms per milliliter of luminal content.

Under normal conditions, yeasts represent a very small fraction of this community, greatly outnumbered by bacteria such as Bacteroides, Firmicutes, and Bifidobacterium.

When the microbiota becomes unbalanced—a phenomenon known as intestinal dysbiosis—yeasts can proliferate until reaching concentrations high enough to ferment significant amounts of carbohydrates.

Several factors favor this anomalous colonization, such as prolonged or aggressive use of broad-spectrum antibiotics, which destroy competing bacteria without affecting yeasts, which lack a bacterial wall.

A diet high in simple carbohydrates provides abundant substrate; short bowel syndrome reduces the absorption surface in the small intestine, displacing unabsorbed carbohydrates to the colon, where they serve as fermentable fuel.

Why can’t the liver always neutralize it?

The adult liver metabolizes approximately 7 to 10 grams of ethanol per hour, equivalent to one standard drink.

When intestinal fermentation is intense — especially after a high carbohydrate intake — ethanol production can exceed that processing capacity.

The excess accumulates in the blood and produces the classic symptoms of intoxication, such as euphoria, disorientation, ataxia, and vomiting, depending on the level reached.

Two variables aggravate this dynamic. First, individual insulin resistance can raise postprandial glycemia, providing more substrate to the yeasts; and certain medications, including some antihistamines and antidepressants, inhibit hepatic ADH activity, further reducing clearance capacity.

The Cordell and McCarthy case (2013)

The case published in the International Journal of Clinical Medicine is the most cited because it was the first to apply a rigorous exclusion protocol.

The patient was hospitalized, given a controlled diet, and his blood alcohol level was measured every few hours over several days.

The results eliminated any possibility of covert consumption: blood ethanol rose after ingesting carbohydrates and decreased during fasting. Stool culture revealed Saccharomyces cerevisiae as the causative organism.

Treatment with fluconazole—an azole antifungal that inhibits ergosterol synthesis in the yeast membrane—combined with a low-carbohydrate diet produced complete remission of the condition.

Blood ethanol levels returned to zero and remained so during follow-up.

The Ohio case (2019)

Six years later, a case published in BMJ Open Gastroenterology expanded the list of causative species.

A middle-aged man presented blood alcohol levels of up to 0.40 g/dL without alcohol consumption. The diagnosis was confirmed with the same controlled hospitalization protocol.

In this case, the identified species was not S. cerevisiae but Saccharomyces boulardii, a strain commonly used as a probiotic for the treatment of diarrhea.

The patient had been taking S. boulardii supplements for months (Malik et al., 2019).

This detail is not anecdotal and highlights that even organisms considered beneficial can behave problematically when established in a gut with pre-existing dysbiosis.

Legal implications

Several courts in the United States have had to rule on this syndrome in cases of driving under the influence of alcohol.

In 2015, a New York court dismissed charges against a driver whose attorney presented medical evidence of the syndrome. The defendant had Saccharomyces cerevisiae in the intestine in abnormal concentrations, confirmed by culture.

In Japan, literature from the 1980s already documented cases related to post-surgical short bowel syndrome that had generated similar legal problems.

These implications reinforce the clinical importance of diagnosis. Auto-brewery syndrome is not a medical curiosity but a disorder with real consequences for those who suffer from it.

Risk factors and diagnosis

The available literature points to several consistent risk factors:

• Previous use of broad-spectrum antibiotics such as fluoroquinolones, cephalosporins, and combinations of beta-lactams with beta-lactamase inhibitors eliminates bacterial competition and opens space for fungal proliferation.
• Short bowel syndrome causes carbohydrate malabsorption in the small intestine; it displaces glucose and starch to the colon, where they ferment.
• Poorly controlled type 2 diabetes, where postprandial hyperglycemia raises the concentration of substrate available to yeasts.
• Autoimmune diseases treated with corticosteroids or immunosuppressants predispose to anomalous fungal colonization.
• A diet high in simple sugars and refined starches such as white bread, polished rice, free sugar, and sugary drinks provides the substrate that feeds fermentation.

How is the syndrome diagnosed?

A definitive diagnosis requires a strict hospital protocol. The patient is admitted to a controlled room where there is no access to any type of alcohol.

A high-carbohydrate diet is established, and blood ethanol levels are measured at regular intervals over twenty-four to forty-eight hours. If blood alcohol rises without alcohol intake, the diagnosis is practically confirmed.

The next step is to identify the causative organism through stool culture, ideally with quantification of yeast colony-forming units. Concentrations above 10⁵ CFU/g are considered diagnostically relevant, although no universally established threshold exists.

Diagnostic errors are frequent; many patients are labeled as covert alcoholics before anyone considers this possibility. The average delay from symptom onset to correct diagnosis is several months, sometimes years.

What treatments exist and how do they work?

The therapeutic approach combines three lines of action:

1. Systemic antifungals

Fluconazole is the first-line drug for cases caused by sensitive Saccharomyces and Candida. Documented regimens in the literature range from two to four weeks of treatment, with doses of 200-400 mg daily.

In strains resistant to fluconazole—some Candida glabrata—alternatives such as voriconazole or amphotericin B are used. Oral nystatin, non-absorbable, is reserved for cases where systemic exposure is to be minimized.

2. Microbiota restoration

Probiotics based on Lactobacillus and Bifidobacterium help repopulate the intestine with organisms that compete with yeasts. Some specialists recommend regimens of several months.

It is important to highlight the paradox of the Ohio case. If the probiotic involved was precisely S. boulardii, the selection of the replacement probiotic must be made with discernment.

Dietary modification

Restriction of simple carbohydrates eliminates the main fermentation substrate. In the most severe cases, a ketogenic diet—below 20-50 grams of net carbohydrates per day—can interrupt the fermentative cycle almost immediately.

Maintaining a low-refined-sugar diet is part of long-term follow-up to prevent recurrence.

What this syndrome teaches about fermentation

For those of us dedicated to the study of beer, auto-brewery syndrome is revealing in a precise sense; it demonstrates that alcoholic fermentation is not an exclusive process of breweries, vineyards, or distilleries.

It is a universal biological process that occurs whenever three elements converge: a source of fermentable carbohydrates, viable yeasts, and anaerobic or microaerophilic conditions.

The human large intestine meets all three requirements. Body temperature—around 37°C—is, by the way, higher than the optimal fermentation temperature for most lager strains (S. pastorianus prefers 8-14°C), but it is within the functional range of S. cerevisiae, which ferments efficiently between 20 and 30°C and tolerates higher temperatures.

The fundamental difference between the intestine and a beer fermenter is not in the chemistry but in control. Strain selection, temperature, sugar concentration, pH, and partial oxygen pressure are controlled variables in production.

In the intestine, they are dynamic variables, influenced by diet, microbiota, the immune system, and individual physiology. This loss of control is precisely what turns a normal physiological process into a disorder.

Understanding this syndrome also helps contextualize why beer fermentation requires such strict conditions; the quality of the final product depends on controlling every variable that, in these people’s intestines, operates without any kind of management.

Frequently Asked Questions (FAQ)

1. What is auto-brewery syndrome?

It is a documented medical disorder in which yeasts present in the large intestine — mainly Saccharomyces cerevisiae or Candida albicans — ferment ingested carbohydrates and produce endogenous ethanol in sufficient quantities to raise blood alcohol levels without the person having consumed alcohol.

2. Is auto-brewery syndrome curable?

Yes. Treatment combines antifungals such as fluconazole or nystatin to eliminate yeasts, probiotics to restore intestinal microbiota, and a diet restricted in simple carbohydrates. Documented cases in medical literature show complete remission with proper medical follow-up.

3. Is auto-brewery syndrome dangerous?

It can be if not diagnosed. Endogenous ethanol levels recorded in clinical cases have exceeded the legal driving limit. Without treatment, chronic exposure to internally produced ethanol can cause progressive liver damage similar to that of conventional alcoholism.

4. What relationship does this syndrome have with beer brewing?

The biochemistry is identical: yeasts metabolizing sugars and producing ethanol and CO₂. The difference lies in control. In a brewery, the process occurs in a sterile fermenter with controlled strain, temperature, and substrate. In the intestine, the variables are dynamic and uncontrolled, which turns a normal process into a disorder.

References

1. Stamation, R. (2025). Endogenous Ethanol Production in the Human Alimentary Tract: A Literature Review. Journal of Gastroenterology and Hepatology, 40(4), 783-790. DOI: 10.1111/jgh.16869
2. Baynes, T., et al. (2021). Gut fermentation syndrome: A systematic review of case reports. United European Gastroenterology Journal, 9(3), 332-342. DOI: 10.1002/ueg2.12062
3. Becker, E. C., Bou Daher, H., Philip, N., & Farmer, A. D. (2025). S5119 The Accidental Brewer: When the Gut Turns into a Brewery. The American Journal of Gastroenterology, 120(10S2), S1093. DOI: 10.14309/01.ajg.0001147936.57849.ee

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