Non-invasive 13C bicarbonate tracer technique for measuring energy expenditure in men – A pilot study

SummaryBackground & aimsEnergy expenditure is an important physiological parameter for providing nutrition guidelines in healthy and ill humans as well as animals. As a potential method for measuring energy expenditure (EE) of human subjects at their habitual physical activity or actual disease condition, the oral stable isotope 13C bicarbonate tracer technique (o13C-BT) is explored for use under routine conditions. The o13C-BT avoids invasive measures like tracer injection, blood sampling or restriction of free movement. This pilot study aimed to determine the accuracy and precision of EE by the o13C-BT examined against indirect calorimetry (IC) in healthy adults.Materials and methodsIn a first experiment, both techniques were applied while the subjects resided in a 4 m3-respiration chamber. After an overnight fast four male volunteers ingested NaH13CO3 (1 mg kg−1). Breath samples were simultaneously collected (A) by sampling from the respiration chamber and (B) by blowing into breath bags. In a second experiment (C), one week later, the determination of EE was repeated in the same individuals under free living, resting conditions by the o13C-BT alone.ResultsEE (kJ d−1 kg−0.75) estimated by the o13C-BT (A: 312 ± 19; B: 331 ± 23) corresponds with the values obtained by IC (329 ± 13). One week later, EE determined by o13C-BT in the same subjects was in an excellent agreement with the preceding estimates (C: 336 ± 22).ConclusionWe conclude that the non-invasive oral o13C-BT is appropriate to estimate EE in free living individuals under routine conditions.