A disease still in the initial stages of investigation causes some individuals to literally get drunk from eating normal amounts of carbohydrates. Originally noticed in Japan, so-called "auto-brewery syndrome" was caused by an abnormal liver enzyme that turns yeast contained in the gut into alcohol.

But new cases have recently surfaced in the US and UK, baffling medical researchers because no such liver enzyme is detectable. Barbara Cordell, head of nursing and health sciences at Panola College in Texas, and her colleague Justin McCarthy, were the first to identify the disorder in the US and have since released a paper studying its causes and effects.

"The problem arises when the yeast in our gut gets out of hand. Bacteria normally keep the yeast in check, but sometimes the yeast takes over," explains Cordell. When you look at the gut environment of people with auto-brewery syndrome, you always find abnormally large numbers of yeast, most commonly a strain called Saccharomyces cerevisiae — what beer makers call "brewers yeast".

Patients who have the disease demonstrate symptoms of drunkenness after eating grains, rice, and other carbohydrates. They can slur their words, feel dizzy and confused, and lose normal motor function. As a result, auto-brewery syndrome has popped up as a defense in some drunk driving cases where police arrested individuals who swore they'd had nothing to drink that evening. 

Police, like physicians unaware of the disease, naturally think the sufferer is drunk: blood-alcohol ratios increase as though the person has been drinking and alcohol is detectible on their breath. When patients are admitted to hospital with symptoms of auto-brewery syndrome, they are suspected of being closet alcoholics. 

Cordell says the condition is most likely caused by antibiotics, which wipes out bacteria in the gut that breaks down and digests yeast. For sufferers of the disease, a diet low in carbohydrates and sugar can eliminate most symptoms. It is helpful, explains Cordell, for physicians to keep an open mind if they encounter a patient with auto-brewery symptoms.

Read more at BBC Future.