Experts advise anyone looking to shed extra kilos to eat less and exercise more. One way is with endurance training, during which the body burns not only carbohydrates such as sugar, but also fat. When exactly the body begins burning fat can now be determined by analysing, for example, biomarkers in the blood or urine. Scientists at ETH Zurich and the University Hospital Zurich have now developed a method for the highly convenient, real-time monitoring of lipolysis by testing a person’s exhalations during exercise.

“When burning fat, the body produces by-products that find their way into the blood,” explains Andreas Güntner, a postdoc in the group of ETH Professor Sotiris Pratsinis. In the pulmonary alveoli, these molecules – especially the volatile ones – enter the air exhaled by the person. The most volatile of these lipid metabolites is acetone. Güntner and his colleagues have developed a small gas sensor that measures the presence of this substance. The sensor is much more sensitive than previous sensors: it can detect a single acetone molecule in hundred million molecules. It also measures acetone exclusively, so the more than 800 other known volatile components in exhalations do not affect the measurement.

Major individual differences

In collaboration with pulmonary specialists at the University Hospital Zurich led by Malcolm Kohler, Professor and Director of the Department of Pulmonology, the researchers tested the functioning of the sensor in volunteers while they exercised. The test subjects completed a one-and-a-half-hour session on a bicycle ergometer with two short breaks. Researchers asked the test subjects to blow into a tube that was connected to the acetone sensor at regular intervals.