Field-deployable measurements of free-living individuals to determine energy balance: fuel substrate usage through δ~(13)C in breath CO_2 and diet through hair δ~(13)C and δ~(15)N values

摘要

Carbon isotopes of breath CO2 vary depending on diet and fuel substrate used. This study examined if exercise-induced delta C-13-CO2 changes in substrate utilization were distinguishable from baseline delta C-13-CO2 variations in a population with uncontrolled diet, and compared hair isotope values and food logs to develop an isotope model of diet. Study participants included nine women with diverse Body Mass Index (BMI), age, ancestry, exercise history, and diet. Breath samples were collected prior to and up to 12 h after a 5- or 10 K walk/run. Indirect calorimetry was measured with a smartphone-enabled mobile colorimetric device, and a field-deployable isotope analyzer measured breath delta C-13-CO2 values. Diet was assessed by food logs and delta C-13, delta N-15 of hair samples. Post-exercise delta C-13-CO2 values increased by 0.54 +/- 1.09 parts per thousand (1 sd, n = 9), implying enhanced carbohydrate burning, while early morning delta C-13-CO2 values were lower than daily averages (p = 0.0043), indicating lipid burning during overnight fasting. Although diurnal delta C-13-CO2 variation (1.90 +/- 0.77 parts per thousand) and participant baseline range (3.06 parts per thousand) exceeded exercise-induced variation, temporal patterns distinguished exercise from dietary isotope effects. Hair delta C-13 and delta N-15 values were consistent with a new dietary isotope model. Notwithstanding the small number of participants, this study introduces a novel combination of techniques to directly monitor energy balance in free-living individuals.