ZURICH (Dispatches)-In the future, a new sensor is going to make it possible to measure the fat the body burns with a convenient breathalyzer in order to test the condition of athletes and people who want to lose weight.
 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.
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.
"We were able to show how the acetone concentration in the exhalations varies greatly from person to person," says Güntner. Scientific opinion used to hold that athletes only begin burning fat after a certain period of physical exertion and on reaching a certain heart rate, but this view is now outdated. The measurements taken by the researchers in Zurich showed that lipolysis in some test subjects did, in fact, only start towards the end of the one-and-a-half-hour training session. In the other volunteers, the measurements showed that their bodies began burning fat much sooner.