A low carb diet can create a false-positive breath test by placing the body in an artificial state of ketosis. WebMD provides a short description of ketosis:
Ketosis is a normal metabolic process, something your body does to keep working. When it doesn't have enough carbohydrates from food for your cells to burn for energy, it burns fat instead. As part of this process, it makes ketones.
If you're healthy and eating a balanced diet, your body controls how much fat it burns, and you don't normally make or use ketones. But when you cut way back on your calories or carbs, your body will switch to ketosis for energy. It can also happen after exercising for a long time and during pregnancy. For people with uncontrolled diabetes, ketosis is a sign of not using enough insulin.
The American Prosecutors Research Institute acknowledges that this is a real concern, addressing it in their manual, "Breath Testing for Prosecutors." APRI states:
Response: Some substances are so similar to ethyl alcohol that early single-wavelength infrared EBTs had difficulty distinguishing them or were unable to distinguish them.Theoretically, these “interfering substances” could inflate breath test results.This is less of a problem than it would seem.There are only a few volatile substances that can be found in the breath of a living, breathing person other than alcohol. Furthermore, when alcohol is present in the breath, it far exceeds in concentration any other volatile components of the breath sample.
In fact, only one potentially interfering substance has been shown to exist in measurable concentrations in the human body over time: acetone. The body produces acetone as a byproduct of incomplete digestion in a very few individuals such as diabetics whose insulin levels are not controlled. If a person is diabetic or fasting, the officer and prosecutor should obtain as much information as possible about the person’s condition or diet.Additionally, people, most notably painters, may be exposed to acetone at work. If a person is exposed to acetone, officers and prosecutors should learn as much as possible about:
• Duration of exposure
• Environment of exposure
• Use of respiratory protective equipment
• Nature of material
• Time between last exposure and breath alcohol test
• Observation of arresting officer
The APRI focuses on acetone, observing that single-wavelength infrared EBTs could "theoretically" inflate breath test results. There's nothing "theoretical" about it, especially regarding single-wavelength infrared EBTs. To the contrary, it is well-known and accepted that a single-wavelength EBT cannot distinguish between ethanol and acetone, which is why most modern breath testing devices employ multiple wavelengths. The BAC Datamaster employs an infrared wavelength of 3.37 and 3.44 um. The Datamaster DMT measures at 3.37, 3.44, and 3.50 um. (Michigan State Police opted to disable the 3.50 um filter for no apparent reason, as well as crippling the Datamaster DMT by disabling the flow, volume and BrAC slope plotting software. In essence, the Datamaster DMT used across the county is wildly different from the Michigan Datamaster DMT, which has been intentionally hobbled by Michigan State Police for no good apparent reason.)
The Datamaster DMT is supposed to trigger a "chemical interference" if enough acetone is present in a breath sample. Although there are concerns regarding the amount of acetone necessary to trigger an error message, it is highly improbable that a Datamaster DMT would provide a reading in excess of the legal limit if only acetone were present. This is not true regarding single-wavelength infrared EBTs, and early advocates of the Atkins diet used older breath testing machines to measure a dieting subject's breath to ensure compliance with the program. Ketonix is a breath testing device that has been specifically designed to measure ketones in a person's breath in connection with the Atkins diet.
Although modern breath testing devices are designed to guard against confusing acetone for alcohol, breath testing devices cannot discriminate between different kinds of alcohol. There are several different kinds of alcohols, including ethanol, methanol, isopropanol, and ethylene glycol. Ethanol is the kind of alcohol contained in alcoholic beverages, but a breath testing device will be unable to distinguish ingested alcohol from other types of alcohols.
But it's not like you're drinking methanol on the Atkins diet, right? Well, not exactly...
An electrochemical detector, such as a PBT device, will respond to "acetaldehyde, methanol, isopropanol and n-propanol vapours besides ethanol, but it was insensitive to acetone vapour." Since these devices do not respond to acetone, a motorist who had a breath interlock testing device inside a company car was surprised when the car would not start. He never consumed alcohol and was a teetotaler, and he was not using mouthwash or any alcohol containing products. He was, however, on a low carb diet, and he was producing ketones consistent with that diet.
In 2007, A.W. Jones published a paper False-positive breath-alcohol test after a ketogenic diet reporting this case. A.W. Jones is one of the world's leading experts on forensic toxicology and human physiology relating to alcohol consumption. Jones reported that:
Since acetone may convert to a significant amount of isopropanol, this is alarming. A dieting person may be under the legal limit, but the isopropanol will be added to the amount of ethanol detected by the Datamaster DMT. There is no filter or safeguard against this based upon the nature of infrared testing.
In Michigan, police officers have the ability to force a motorist to submit to a breath, blood, or urine test under Michigan's implied consent laws. A blood test will not be effected by the presence of isopropanol. As Jones reports, "[t]he reduction of acetone to isopropanol is not a problem with blood-ethanol determination because gas chromatography is used and this highly specific method can resolve ethanol from both acetone and isopropanol under normal operating conditions." Given that officers have the choice of which test to administer, they should make inquiries regarding a person's diet, opting to administer a blood test following an arrest for suspected DUI whenever a person reports being on a low carb diet.