Can a low-carb diet lead to a false-positive breathalyzer result?

The basic idea behind low-carb dieting is simple: by denying the body a food supply of carbohydrates to convert into energy, you can force it to burn its fat reserves instead through a process known as “ketosis.” Research suggests that this may be a mixed blessing, however, if you should ever find yourself the subject of a breathalyzer test.
How can a low-carb diet trigger a false positive?
To understand how ketosis can contribute to skewed breath test readings for alcohol, the first thing to consider is that there are different types of alcohol. Most people are familiar with ethanol, the “grain alcohol” that is found in alcoholic beverages, and methanol, or “wood alcohol” that is unfit for human consumption; but other forms exist as well, like isopropanol and ethylene glycol. All of these variations have at least one thing in common, a breathalyzer cannot differentiate among them; and ketosis can have the effect of creating isopropanol that a breathalyzer can detect in the same way as ethanol.
Here is how the process works:
1. When you do not consume enough carbohydrates, the body breaks down fat cells for energy (ketosis can also result from prolonged exercise or from diabetes).
2. A byproduct of ketosis is ketones; and one form of ketone is acetone.
3. Acetone breaks down into isopropanol in the body, which a breathalyzer or an ignition interlock device cannot tell apart from ethanol.
Although modern breathalyzer devices can tell the difference between acetone and alcohol, incidents have still been recorded in which a person who has consumed little or no alcohol, but who is producing ketones that have converted into isopropanol, has generated a false positive breath test sample for alcohol.
What does this mean for you?
Chances are that if you have not been drinking alcohol, but have been generating ketones through one of the ways described above, you will not have enough isopropanol in your system to trigger a .08 reading from a breath test (that is, you can’t “get drunk” from ketosis). A problem can still occur, however, when you have consumed alcohol — not enough to reach the DUI threshold — and the ketone-to-acetone-to-isopropanol breakdown produces just enough isopropanol in your breath to fool the breathalyzer or ignition interlock into reading that you have indeed exceeded the legal limit.
This false-positive possibility is known to law enforcement, and a trained police officer can seek to avoid it by asking you questions meant to identify whether you have been engaged in activities or exposed to environments such as painting that could produce acetone in your system. Another way that police may try to confirm whether your over-the-limit BAC reading is measuring ethanol is by obtaining a blood sample for analysis (blood tests are not subject to the confusion of different alcohol types that breathalyzers are).
If you have been subjected to a breathalyzer test that indicates you were DUI, that test result is not necessarily as damning to your legal defense as it might seem on the surface. Ketosis-generated alcohol in your system is one way that a breath test can produce an inaccurate result; it is not the only way. An experienced DUI defense attorney will know what to look for when working with you to see if one or more challenges exist to a breathalyzer result that can work to your advantage.