Several recent cases in South Carolina and other states have uncovered a strange problem where drivers on a keto diet produce positive results for alcohol intoxication even when they haven’t been drinking. During ketosis, the liver increases its breakdown of fat, producing acetone. This chemical is partially evaporated as isopropyl alcohol. A breathalyzer can’t distinguish this from consumed alcohol that results from drinking according to many medical professionals, leading to a false positive.

Companies that manufacture fuel-celled breathalyzers, which are the type used by the police during traffic stops, claim that their devices can tell the difference between isopropyl alcohol and ethanol. A professor from Sweden’s Linköping University, however, says that there is no peer-reviewed data that shows these devices are able to tell the difference. Either way, however, BAC test results done during a field stop won’t be used to convict. Tests conducted at the police station use infrared spectroscopy, which can tell the difference between alcohol types, will be admitted for evidence at trial.

Experts believe that it’s unlikely that acetone production from ketosis alone could cause a person to blow above the legal limit. The concern here is for drivers who already have a DUI on their record who could be penalized for a BAC as low as .02 which is possible from keto alone. Other factors, such as diabetes and acid reflux, can also result in false positives.

Drivers accused of drunk driver have the right to representation from an attorney who practices criminal defense. It’s the responsibility of a lawyer to make sure evidence of their client’s BAC was obtained legally and that the results are accurate. Alcohol testing can be very complicated: Lawyers may be up-to-date on the latest research and case law regarding breathalyzers, blood tests, and other detection methods.