Lumen is a handheld metabolism tracking device that utilizes breath analysis to assess whether the body is primarily burning fats or carbohydrates as a source of energy. Through a CO₂-based measurement, the device provides users with real-time insights into their metabolic state. By integrating with apps such as Apple Health, Google Fit, and Garmin, Lumen can account for variables like nutrition, physical activity, sleep, and stress patterns to offer personalized feedback. Each breath sample is analyzed with a proprietary algorithm, which may result in a tailored nutrition and lifestyle guidance through the Lumen app. Users receive daily recommendations that can adjust based on inputs like exercise or menstrual cycle phases. Lumen allows on-demand metabolic readings and records trends over time to reflect patterns and shifts in metabolic flexibility. According to the information available, Lumen’s device performance has been evaluated against a gold-standard metabolic cart and is supported by multiple peer-reviewed studies. The device comes with a one-year warranty from the date of account activation or ten days after purchase, whichever occurs first.