Oct. 29, 2019 -- A man who said he never drank alcohol but often appeared drunk actually had a rare condition called auto-brewery syndrome, in which his gut began producing alcohol whenever he ate carbohydrates, a new case study says.

For years, the 46-year-old man's family, doctors and police thought he was a closet drinker, despite his insistence that he didn't drink any alcohol, NBC News reported.

The man displayed "brain fog and aggressive behavior," fell often, and was even arrested for suspicion of driving while intoxicated.

He was eventually diagnosed with auto-brewery syndrome, which occurs when "gut disturbances" -- including antibiotic use -- result in uncurbed growth of fermenting fungi or bacteria in the gastrointestinal tract, NBC News reported.

When carbs such as pizza, pasta, bread and soda are consumed, these microbes turn the sugar in that food or drink into ethanol, leading to "extreme blood alcohol levels," according to the study by doctors at the Richmond University Medical Center in New York that appears in the journal BMJ Open Gastroenterology.

In this case, the man's troubles began in 2011 after he was prescribed antibiotics for a thumb injury, NBC News reported.

After years of struggle, the man was treated with antifungals and began taking probiotics, which promote the growth of good bacteria in the digestive system. His symptoms went away and he eventually resumed eating a normal diet, according to the study.