Are ketosis strips about to be a thing of the past? Scientists have developed a reliable acetone detecting device that can estimate how much fat you’re burning with a puff of air. A team of engineers and diabetes specialists, helmed by Prof. Dr Andreas Güntner, Assistant Professor at the Department of Mechanical and Process Engineering, ETH Zürich, reported this July that they have invented a smart phone accessory that turns your device into an acetone breathalyzer.
Similar to an alcohol breathalyzer, this new piece of kit can detect the percentage of acetone in your breath. An app on your smart phone then crunches the numbers to convert this into an estimate of how much fat your body is currently metabolizing. While there are acetone breathalyzers on the market right now, the academics claim that their device sets a new standard for accuracy and consistency.
In a research paper published in the scientific journal Device, the inventors demonstrated that their acetone breathalyzer performs consistently between devices and in varying humidity conditions over at least eight months. Perhaps most importantly, its measurements line up with the gold standard of breath analysis – laboratory mass spectrometry.
Every Breath You Take
If you aren’t a biohacker or keto diet enthusiast, you might be asking yourself what any of this means. Basically, when we run out of glucose to power our cells, our bodies go to a back-up energy supply – fat. We call the chemical process that converts fat into energy, ‘ketosis’. We use enzymes in our cells to break fats down into ketones, breaking the chemical bonds between molecules in fats releases energy. Making ketones from fats is the process of ketosis.
Ketones are a waste product like urea in our urine and carbon dioxide on our breath. We get rid of them in our urine and by breathing them out. Acetone is a ketone that we exhale along with water vapour, carbon dioxide, etc. We can estimate how much fat we’re burning based on how much acetone we breathe out. The more acetone on our breath, the more of our fat stores we are using up.
The idea of low carb and ketogenic diets is to push our bodies to use up our fat stores instead of metabolizing glucose derived from carbs.
Does an acetone breathalyzer really need to be that accurate? As Güntner explained in a press release, ‘Methods are also needed that can be carried out independently and that produce reliable results, similar to blood glucose measurements for diabetics.’ While most of us equate acetone or ketosis monitoring with weight loss, it is also a useful indicator for epileptics following a ketogenic diet and high-risk diabetics to make sure that they are managing their diet effectively. For diabetics in particular, ketosis can be a warning sign that their blood glucose levels are dangerously low.
Canary in a Coal Mine
Right now people rely on blood tests and urine dip sticks for reliable measures of ketosis. The current generation of acetone breathalyzers are expensive, bulky and don’t always give the level of consistency that users need.
What’s more, an acetone reading in isolation isn’t necessarily that useful. To really understand what’s going on with our metabolism, we need to track our acetone levels reliably over a period of time, keeping careful records to figure out how they are changing.
The problems with acetone breathalyzers centre around three aspects: user error, our environment and the mechanics of the breathalyzer itself. To get an accurate and consistent read out, you need to use the breathalyzer the same every time. If you ate or drank something recently, it can change the molecular profile of your breath, confusing the machine. If you don’t blow the same way each time, your reading won’t be accurate. Then, on top of that, you need to keep track of your readings.
Even the air around you needs to be consistent. Humidity in the air can change the proportion of acetone in your breath a typical breathalyzer will record. Some breathalyzers aren’t even calibrated to precisely detect acetone amongst a bunch of other similar chemicals.
With all these limitations, a typical home acetone breathalyzer is a useful tool. The read-out it gives, however, will never be accurate enough to detect small metabolic changes or trends over a short period of time, so blood tests and urine strips win the day.
Message in Bottle
Güntner and his team aimed to solve these problems by hitching a special breath sensor with a built-in filter to a smart phone.
The addition of the filter and the specialized sensor improve the device’s performance by safeguarding against contaminants from food and drink and by correcting for differences in humidity. A sophisticated air filtration system uses air pressure to pinpoint the amount of puff needed and carefully separates out the compounds in the breath. This controlled breath sampling allows the device to account for ambient humidity as the compounds flow over a special sensor calibrated to detect acetone.
The breathalyzer filter transits information via Bluetooth to the app. It tells the user whether you are breathing hard enough and long enough to make sure it’s measuring the same part of your breath every time. This, the researchers say, is vital to ensuring a consistent reading.
‘The device measures the volume of exhaled air and only takes a sample that comes from deep in the lungs after a certain time,’ says lead author Simone Hersberger, adding: ‘Otherwise, every reading would be slightly different.’
Next the sensor sends the acetone measurement to the app, which stores it exactly as read, for future analysis. The app can show you trends over time and alert you to changes that need attention. With the filter ensuring a clean and consistent sample every time and the improved sensor, the team hope to slim down enough of these variables to boost their device’s sensitivity and reliability.
That’s all very good to say, but does it work? Hersberger certainly thinks so. ‘We were able to demonstrate that our device can detect slight differences in fat metabolism accurately and reliably.’ But how can they be sure?
On Any Other Data
The researchers challenged their device to perform as well as the most sensitive analytical device for identifying chemical signatures in gas samples – laboratory mass spectrometry. They recruited twelve healthy volunteers to test the acetone breathalyzer to its limits. The team compared readings from the breathalyzer to mass spectrometry results on breath samples collected within minutes. The agreement between the devices’ measurements of acetone parts per million and that of the mass spectrometry was very high. Consistently the researchers reported correlation r values of more than 0.9 when tested against samples taken at rest, after exercise and from people on a ketogenic diet. Participants were a mix of male and female volunteers aged between 20 and 37. Repeated readings were collected over a period of up to eight months.
The team used several different mass spec techniques to cross-validate the results and found R values close to 1 consistently in the first few months of use.
All the distributed devices performed similarly in terms of repeatability and accuracy as compared to laboratory measures. Even after eight months of repeated exposure to human breath, the devices performed well.
The researchers were able to show changes in acetone on people’s breath within eight hours of exercise, and they could see differences in acetone profiles between participants on carb rich, fat rich and fasting diets.
It’ll probably be a while before we see the device on pharmacy shelves along with glucose monitors and ketosis strips. With a Zürich-based university spin off business handling the next steps of research and development we might not be waiting long.
Hersberger S, Broek J van den, Schmid L, Kappeler F, Gerber PA, Güntner AT. Self-monitoring of fat metabolic status with smartphone-assisted breath acetone detector. Device. 2026;0(0). doi:10.1016/j.device.2026.101226
