ETH Zurich researchers have developed a handheld, smartphone-assisted breath analyzer that measures acetone to indicate fat metabolism, delivering lab-grade accuracy in about 90 seconds. In a validation study with 12 healthy adults and 312 breath samples, the device’s readings closely matched those from mass spectrometry across various metabolic scenarios, including different exercise intensities and diets. The system guides users through proper breathing via a companion app to ensure reliable samples, and includes filters and quality controls to minimize interference from moisture and contaminants. The technology, branded as Nutrion by the ETH spin-off Alivion, is being explored for clinical monitoring of obesity, diabetes, epilepsy, intermittent fasting, and ketogenic therapies, offering a potential alternative to repeated finger-prick blood tests. Experts stress that rapid, at-home measurements could enable personalized diet plans and treatment adjustments based on an individual’s fat-burning state. The research underscores a move toward accessible, precise metabolic monitoring outside traditional laboratories.