Some people in Illinois on low-carb diets may blow false positives on alcohol breath tests. This happened to a man in Texas whose diet put him in ketosis. His attorney was able to get his DUI dismissed.

The reason is that the fat broken down during ketosis may release a byproduct, acetone, that becomes isopropyl alcohol when a person breathes it out. Not all breath tests can distinguish between this and ethanol alcohol although manufacturers say the types that police carry can. However, the attorney who got the Texas case dismissed says that there have been no studies proving that the devices can tell the difference if a person is breathing a mix of isopropyl and ethanol alcohol. If a person who is in ketosis has a small amount to drink, that person could appear to have an inaccurately high blood alcohol content.

One paper published in 2006 examined a man’s difficulty to start a company-owned vehicle that required a breath test. The man was on a low-carb diet. The paper argued that fuel cell breath analyzers could not tell the difference in ethanol and acetone that had been converted to isopropanol.

Most law enforcement agencies have a device back at the station that uses infrared spectroscopy and can distinguish between the types of alcohol. A person may also be able to request a blood test.

Even a first-time DUI conviction can have significant repercussions. In addition to penalties that could include a fine or jail time, DUIs may also affect some people’s careers. People who are facing DUI-related charges may want to contact an attorney to discuss options for DUI defense. This might include challenging the results of a Breathalyzer test. A person’s attorney may also question law enforcement’s report of what happened or look into whether the person’s rights were violated.