A Belgian man with a very rare metabolic condition that causes his body to produce alcohol had a drink-driving charge against him dismissed in court on Monday.

The 40-year-old proved that he has auto-brewery syndrome (ABS), which causes carbohydrates in his stomach to be fermented, increasing ethanol levels in his blood and resulting in signs of intoxication.

His lawyer, Anse Ghesquiere, confirmed the unusual case to AFP after Belgian media reported on it.

She said scientists believe that the number of ABS cases in the world is under-estimated. Currently, only some 20 people globally have been officially diagnosed with the condition.

She stressed that her client -- whose identity was not given -- gave evidence of his ABS after tests run by three doctors.

The court recognised that factors unforeseen by law applied to the man's case and acquitted him of the charge.

He ended up in court after police in April 2022 pulled his vehicle over and registered him giving a breathalyser reading of 0.91 milligrammes of alcohol per litre, and again a month later when his breath contained 0.71 milligrammes.

The legal limit in Belgium is 0.22 milligrammes per litre of air exhaled, which corresponds to a blood alcohol level of 0.5 grammes per litre.

Previously, in 2019, the man had received a fine and a driving licence suspension despite protesting that he had not drunk any alcohol.

He was apparently unaware of his syndrome before his latest run-in with police.

Ghesquiere said she and her client were awaiting formal notification of the acquittal. She noted that the prosecution service had a month to lodge an appeal if it wished to do so.

The man meanwhile was following a carbohydrate-light diet to avoid his stomach producing more alcohol.

At his initial court appearance in March, the prosecutor requested he avoid any alcoholic beverages, the Belgian state television channel VRT reported.