Belgian Driver Acquitted After 3.56 Promille Due to Auto-Brewery Syndrome

A 42-year-old driver from Kuurne, West Flanders, has been acquitted of drunk driving charges despite registering a blood alcohol level of 3.56 promille — more than seven times the Belgian legal limit of 0.5 promille. The police court accepted the man’s defense that he suffers from auto-brewery syndrome (ABS), an extremely rare medical condition in which the body naturally produces alcohol through fermentation of carbohydrates in the gut.

The Incident and Diagnosis

On May 11, 2025, police in Kortrijk stopped K.C. (initials only) during a routine traffic check. The breathalyzer result was staggering: 3.56 promille, a level that would typically indicate severe intoxication and could be life-threatening for most people. The driver admitted to having consumed two glasses of cava with his partner to celebrate their engagement but insisted this could not account for such an extreme reading.

According to Het Laatste Nieuws, the mystery was solved during a vacation in Germany in summer 2025, when K.C. suffered a sudden epileptic seizure and was hospitalized. Doctors there diagnosed him with auto-brewery syndrome (autobrouwerijsyndroom), a condition where the body itself converts carbohydrates and sugars into alcohol.

“The doctors discovered that he suffers from the so-called auto-brewery syndrome, an extremely rare syndrome where the body itself converts carbohydrates and various sugars into alcohol,” said his lawyer, Thomas Vandemeulebroucke.

What is Auto-Brewery Syndrome?

Auto-brewery syndrome, also known as gut fermentation syndrome, is an exceptionally rare medical condition affecting only approximately 15 confirmed individuals worldwide. It occurs when an overgrowth of fermenting yeasts and bacteria — particularly Saccharomyces cerevisiae and Candida species — in the gastrointestinal tract causes the body to produce ethanol through endogenous fermentation.

Toxicologist Jan Tytgat, who provided expert commentary on the case, explained: “We all actually have a little bit of alcohol in our bodies. That’s because bacteria ferment in our large intestine. But that involves extremely small amounts.” He noted that the levels recorded in these cases are extraordinarily high, adding: “The amounts are very high, so I am inclined to be critical. But if it’s been established and scientifically proven, who am I to contradict that?”

The Court’s Decision

The court appointed a medical expert who confirmed the ABS diagnosis and deemed K.C. fit to drive on the condition that he follows a strict low-carbohydrate diet. The judge acquitted the driver on grounds of force majeure (overmacht), ruling that it is impossible to accurately determine his alcohol level when he has consumed alcohol, given his condition.

K.C.’s lawyer described the toll the ordeal took on his client: “His life was turned upside down for months. He stopped working and no longer drove. His wife didn’t even trust him when he went out on his bicycle.”

A Remarkable Coincidence in West Flanders

Remarkably, this is the second such case in Belgium’s West Flanders province. A 40-year-old man from Bruges was acquitted in April 2024 under similar circumstances, as reported by Het Laatste Nieuws. He was stopped twice — on April 2, 2022 (2.09 promille) and May 7, 2022 (1.63 promille) — before being diagnosed. The Bruges driver, who ironically works for a brewery, now follows a strict diet avoiding apples, bread, and cola to prevent his body from producing alcohol.

Both diagnosed ABS cases in Belgium live in the same province, approximately 50 kilometers apart — a striking concentration given the condition’s global rarity.

Legal Implications and Public Safety

The acquittals establish a growing legal precedent in Belgium for recognizing auto-brewery syndrome as a valid medical defense against drunk driving charges. However, the court warned both drivers that now they are aware of their condition, future violations while not adhering to their diets could result in conviction.

The cases raise important questions about road safety and medical monitoring. While the court deemed both drivers fit to drive on strict diets, concerns remain about how compliance will be monitored and what happens if trigger foods are consumed unknowingly. Some commentators have suggested that alcohol ignition interlock devices could provide an additional safety measure.

What’s Next

As awareness of auto-brewery syndrome grows, medical professionals hope that others with undiagnosed ABS may come forward. For now, the two West Flanders drivers must carefully manage their diets to avoid triggering alcohol production. Their cases highlight the complex intersection of rare medical conditions and legal responsibility — and the challenges courts face when science presents an explanation that defies common assumptions.