Lumen, a health technology company, has launched the Lumen, a handheld, portable device and app that measures your metabolism in real-time with just your breath. 

The company says it’s making personal, at home metabolic tracking available outside of research labs for the first time. The Lumen works by measuring your body’s carbon dioxide concentration by breathing into the handheld device. These levels indicate the type of fuel your body is using to produce energy – a mix of fat or carbs.

The Lumen provides you with personalized suggestions on when and what to eat to fuel your workout, based on your metabolism. It supports fat burn and purportedly improves your metabolic flexibility, which is your body’s ability to efficiently switch between using carbs and fats as a fuel source.

The US$349 Lumen device is available at lumen.me. The device comes equipped with a travel case, charging dock, USB-C Cable, and Premium Customer Support. Users can download the app for free on the Apple App Store and on Google Play.