Lumen

Lumen provides one metabolic signal within a broader tracking picture rather than replacing all other metrics. Lumen is presented as a consumer-friendly adaptation of indirect calorimetry. Lumen estimates whether the body is using fat, carbohydrates, or both by measuring carbon dioxide in exhaled breath after a controlled breathing maneuver. The breath hold is described as making exhaled carbon dioxide more reflective of blood carbon dioxide and current fuel use. Lumen requires a specific breath maneuver rather than ordinary breathing.