Ketogenic (Keto) and low carbohydrate diets are among the more popular eating lifestyles these days. Someone on a strict Keto or other low carb diet metabolizes energy differently than a person who is eating a normal amount of carbs. The liver of a person on such diets breaks down fat for fuel, which creates acetone that may be released through the person’s breath. This is colloquially referred to a “being in ketosis.” The acetone can be reduced to isopropyl alcohol depending on the stage of ketosis
Anecdotal evidence (and a few scientific papers) supports a potential concern that someone on a Keto diet could cause a false positive on a breathalyzer. While the breath molecules expelled by a person in ketosis will not turn a 0.00% blood alcohol content (BAC)into a 0.08% BAC, a Keto diet may cause a breathalyzer to register over 0.08% for someone who, if not on a Keto diet, may have registered something below that. For example, someone who is in ketosis and has had a couple of drinks and might have a 0.06% true BAC, could potentially register 0.08% or more.
Law enforcement agencies use fuel cell breathalyzers, which supposedly can differentiate between ethanol molecules (those created by drinking alcohol) and other alcohol-based molecules, such as the Isopropyl molecules expelled when someone is in ketosis. However, I am unaware of any data that support this. While a blood test for BAC can establish that the driver’s BAC is under 0.08%, this can become more than an inconvenience for the driver. Beyond that, the driver who unwittingly chooses a breath test rather than a blood chemical test, may be stuck with a false positive result. A lesson here might be that if your