The Association of Macronutrient Consumption and BMI to Exhaled Carbon Dioxide in Lumen Users: Retrospective...

Metabolic flexibility is the ability of the body to rapidly switch between fuel sources based on their accessibility and metabolic requirements. High metabolic flexibility is associated with improved health outcomes and a reduced risk of several metabolic disorders. Metabolic flexibility can be improved through lifestyle changes, such as increasing physical activity and eating a balanced macronutrient diet. Lumen is a small handheld device that measures metabolic fuel usage through exhaled carbon dioxide (CO₂), which allows individuals to monitor their metabolic flexibility and make lifestyle changes to enhance it.

This retrospective study aims to examine the postprandial CO₂ response to meals logged by Lumen users and its relationship with macronutrient intake and BMI.

We analyzed deidentified data from 2607 Lumen users who logged their meals and measured their exhaled CO₂ before and after those meals between May 1, 2023, and October 18, 2023. A linear mixed model was fitted to test the association between macronutrient consumption, BMI, age, and gender to the postprandial CO₂ response, followed by a 2-way ANOVA.

The model demonstrated significant associations (P<.001) between CO₂ response after meals and both BMI and carbohydrate intake (BMI: β=-0.112, 95% CI -0.156 to -0.069; carbohydrates: β=0.046, 95% CI 0.034-0.058). In addition, a 2-way ANOVA revealed that higher carbohydrate intake resulted in a higher CO₂ response compared to low carbohydrate intake (F_2,2569=24.23; P<.001), and users with high BMI showed modest responses to meals compared with low BMI (F_2,2569=5.88; P=.003).

In this study, we show that Lumen's CO₂ response is influenced both by macronutrient consumption and BMI. The results of this study highlight a distinct pattern of reduced metabolic flexibility in users with obesity, indicating the value of Lumen for assessing postprandial metabolic flexibility.