Lumen
Portable metabolism analyzer that measures your respiratory exchanges to tell you if you are burning fat or carbs
Overview
Lumen is a pocket device that measures the CO₂/O₂ ratio in your breath to determine in real time if your metabolism is using primarily fat or carbs as an energy source. Each morning, you breathe into the device and the AI app analyzes your metabolic level (1-5) to personalize your macronutrient intake for the day, with nutritional recommendations adapted to your physical activity and goal (fat loss, sports performance, metabolic flexibility).
Lumen targets athletes and nutrition-conscious individuals wanting to optimize their diet based on real metabolic state, particularly those practicing ketogenic diets, intermittent fasting, or carb periodization. The device is an investment (>$300) with a mandatory monthly subscription after the first month. The app is English only. Integrations are extensive (Garmin, Apple Health, Strava, Oura, WHOOP), making it a metabolic data hub for multi-device users.
Our verdict
Best for athletes and advanced nutrition practitioners wanting real biochemical data to personalize their diet around training. Not for you if you are looking for a simple calorie tracker: the device plus subscription cost is high for casual use, and the lack of a French version limits adoption.