Device Tracks Fat Burning Through Exhaled Breath

Acetone is the by-product of fat metabolism that is exhaled via the lungs. It is made when the body burns fat instead of carbohydrates such as sugar. Researchers from ETH Zurich have developed a breath test device that can detect acetone in exhaled air with high precision. The device is very reminiscent of the alcohol breathalysers used by the police in traffic checks and can be operated reliably by non-experts in combination with a smartphone app. People can therefore monitor their fat metabolism without professional support or blood tests. This could eventually allow diets, treatments for metabolic disorders like diabetes, and ketogenic therapies used for example for epilepsy to be monitored more closely and tailored to individual patients.

"When it comes to diets, there's no rule of thumb that works for everybody. Ideally, people should self-monitor to see how their own metabolism responds," explains Andreas Güntner, Professor of Molecular Sensing at ETH Zurich's Department of Mechanical and Process Engineering. "Methods are also needed that can be carried out independently and that produce reliable results, similar to blood glucose measurements for diabetics." Güntner's research group developed the measuring device in collaboration with the ETH spin-off Alivion, and tested its reliability together with the University Hospital Zurich.

Precise measurements outside the lab 

In a validation study involving 12 adults, the researchers compared 312 breath readings recorded with the new measuring device with blood test results and measurements from a high-precision mass spectrometer - the analytical gold standard. The measurements were carried out using different metabolic scenarios: with light and intensive physical activity and various diets. This revealed that the results from the hand-held device were practically identical to those from the lab. In addition, the new measuring device delivered reliable results over a period of months.

In essence, the recently tested hand-held device is based on a sensor technology that has been in development at ETH Zurich for over 10 years and was presented for the first time in 2017. Already at the time, Güntner and his co-authors were able to demonstrate that the gas sensors they had developed were so sensitive that they could detect a single acetone molecule in a hundred million other molecules.

Reproducible readings thanks to filter and app

According to the researchers, readings from currently available acetone breathalysers have only limited reproducibility and can only detect pronounced metabolic changes. They not only respond to acetone, but also to other components of exhaled air, for example if test subjects ate or drunk something beforehand.

The researchers therefore developed a filter that blocks interfering molecules, and a smartphone app that guides test subjects in real time as they exhale. "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." In order for this to work, the devices are initially calibrated and adjusted to the patient's lung volume.

From basic research to product 

The successful validation study is an important milestone for the researchers. "We were able to demonstrate that our device can detect slight differences in fat metabolism accurately and reliably," says ETH doctoral student Hersberger. Further studies are now intended to show whether the new measuring device can really be used to personalise therapies for metabolic disorders. In partnership with the University Children's Hospital Zurich, the researchers are currently looking at whether the hand-held device can help children with epilepsy better monitor their ketogenic diet. Other fields of application are the monitoring and optimisation of medical diets or of so-called GLP-1 therapies with weight loss jabs. Applications in amateur sports are also being considered.

The ETH spin-off Alivion AG has launched the device under the name 'Nutrion'. It is currently being deployed in international research studies and in medical facilities. To scale up further and to open up further fields of application, Alivion is seeking additional industry partners and strategic investors. "This example shows how the results of basic research can be put into practice and ultimately help society," says ETH professor Andreas Güntner.

This work is being financially supported by Innosuisse, the Vontobel Foundation and the Accentus Foundation.