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Can the keto diet trick a breathalyzer into a false positive?

A DUI case in Texas was recently dismissed. The defendant performed well on a field sobriety test, but the police breathalyzer pegged him at well above the limit. According to his defense attorney, the reason was completely innocent: he was on the keto diet, and it had skewed his breathalyzer results.

Low-carbohydrate diets like the keto diet work by putting the body into a state of ketosis. During ketosis, the liver breaks down body fat and uses it for fuel. This process creates acetone, which is then released through the breath as isopropyl alcohol. This is not the same alcohol that can get you drunk -- that is called ethanol. Is it possible that breathalyzer tests could confuse isopropyl alcohol with ethanol and wrongly declare someone intoxicated?

It ight be. Two experts interviewed on the subject for Men's Health magazine agreed that inexpensive personal breathalyzers probably can't differentiate between the two types of alcohol, so a person on the keto diet might test as more intoxicated than they actually were.

The versions used by police, however, use a different technology than the ones people buy to monitor their own blood alcohol content. And, according to Men's Health, the manufacturers of police breathalyzers say their devices can tell the difference between isopropyl alcohol and ethanol. Allegedly, only ethanol is counted in the test result.

That said, a criminal defense attorney told Men's Health that he had been unable to find any peer-reviewed studies proving these devices can differentiate.

Ultimately, ketosis probably wouldn't create enough isopropyl alcohol in your breath to cause a positive test result if you had not been drinking. If a breathalyzer could not differentiate the two alcohols, however, the isopropyl alcohol might be enough to put you over the limit when you would otherwise be just under it.

Keto might affect ignition interlock devices

There are few published papers on this topic, but one Swedish researcher found that acetone sometimes gets converted to isopropanol, which might be more difficult to differentiate from ethanol. It is oxidized by police-style breathalyzers in the same way as ethanol.

In his paper, he noted that a man on a low-carb diet struggled to start a company car that was fitted with an ignition interlock. The engine wouldn't start unless the driver tested lower than 0.02, but the man in ketosis couldn't start it.

If you have been charged with DUI and are on a low-carb diet, you should definitely share this information with your defense attorney. Also, other medical conditions such as diabetes can interfere with breathalyzers. Being on the keto diet will not get you a free pass on a DUI charge, but hiring an experienced DUI attorney can help determine what role, if any, the diet could have had on alcohol results.

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