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Could a Low-Carb Diet Affect the Results of A Breathalyzer Test?

The Collin County Law Group March 6, 2019

In 2006, a Swedish researcher published a paper on the effect of low-carb diets on breath testing machines. He profiled a man who struggled to start a company vehicle fitted with an ignition interlock device even though he was completely sober. An ignition interlock is a breath-testing machine that won’t allow a vehicle to start unless the driver provides a clean breath sample — typically less than 0.02 percent.

This man’s low-carb diet put his body into a state of ketosis, which creates acetone in the body. That acetone gets converted by the body into isopropyl alcohol. Although isopropyl alcohol isn’t the intoxicating kind, its presence in the breath can be misread by some breath testing technologies. It was apparently the presence of isopropyl alcohol in the man’s breath that triggered the ignition interlock.

In other words, there may be circumstances when being on the Keto diet (or another low-carb diet) could push your breathalyzer results higher than they might otherwise be. For example, if you were really at 0.065 percent, being on the Keto diet could push your results to as high as 0.085 percent — over the legal limit.

How Plausible Is the Keto Diet as A DWI Defense?

Men’s Health magazine recently looked into the question, and the answer is still unclear. The magazine found one example of a Texas DWI case that was tossed out because the driver was on a low-carb diet. He apparently blew well above the limit but passed a field sobriety test.

Before you assume you’ve got a get-out-of-jail-free card, however, consider what else Men’s Health found out. The magazine interviewed the CEO of a breath testing machine company to find out if breathalyzers can tell the difference between isopropyl alcohol and the type of alcohol people drink, which is called ethanol.

First, he noted that the personal breathalyzers people buy to gauge their own blood alcohol levels probably can’t differentiate between isopropyl and ethanol alcohols. These devices work by measuring the number of alcohol molecules that strike a metal film, changing its resistance.

That said, the breath testing devices used by police use a different technology. They are based on fuel cells. Breath tester manufacturers, including the CEO interviewed by Men’s Health, insist that these devices are able to differentiate between the two types of alcohol.

Can they? It’s hard to say without peer-reviewed studies explaining just what the devices can and can’t do. It could be especially complex when a person in ketosis drinks alcohol, mixing the ethanol and isopropyl alcohol in the breath.

The upshot? If you’re on a low-carb diet and get pulled over for DWI, you should definitely mention that fact to your DWI attorney. Whether the diet would affect your results is hard to say and would depend on the machine used to gauge your blood alcohol content. Moreover, you may have been subjected to a blood or urine test that gave a different result. All of these factors should be considered when planning your DWI defense strategy.