Immediate biofeedback for energy balance via expired breath δ13CO2

Expired breath δ¹³CO₂ measured in real time serves as a useful biomarker of altered macronutrient metabolism in response to changes in energy balance. Altered breath δ¹³CO₂ is believed to be a result of changes in macronutrient oxidation and the kinetic isotope effect where enzymatic processes discriminate against metabolites naturally enriched with ¹³C. Use of breath δ¹³CO₂ as a rapid biofeedback of energy balance status will enhance an individual´s ability to modify behavior during weight loss efforts. Herein we describe a novel approach for immediate biofeedback for energy deficit using a moderate exercise challenge. Our new mid-infrared isotope ratio-meter for δ¹³CO₂ is a step toward miniaturization of a personal device for instant biofeedback for people attempting to lose weight.