An Overnight, 8-Hour Low Oxygen Exposure Increases Energy Expenditure with No Effect on Energy Intake: A Randomized, Sham-Controlled, Crossover Study

BACKGROUND: Extended exposure to hypobaric hypoxia at high altitude induces negative energy balance through elevations in resting metabolic rate (RMR) and decreases in energy intake. It is unknown if an overnight bout of normobaric hypoxic (NH) exposure at sea level induces similar changes in energy balance and associated mechanisms. OBJECTIVES: The aim of this study is to determine the effects of a single overnight exposure to NH on RMR, heart rate (HR) variability (HRV), appetite, and energy intake compared with an overnight exposure to normobaric normoxia (NN) in normal-weight adults. METHODS: , 24.5 ± 3.9 y) slept 8 h in a tent maintained at either ∼15% (∼2640 m elevation) or ∼20% oxygen (∼305m elevation). The following morning, HRV was measured inside the tent using electrocardiography; RMR was measured outside the tent using indirect calorimetry; and energy intake and subjective appetite were assessed outside the tent with an ad libitum breakfast buffet and visual analog scales, respectively. RESULTS: , P-condition = 0.052, respectively). HR was greater in NH (61.3 ± 7.4 bpm) compared with NN (56.2 ± 7.6 bpm; P-condition < 0.0001). RMR was elevated in NH (1.07 ± 0.18 kcal/min) compared with NN (1.04 ± 0.13 kcal/min; P-condition = 0.018). Appetite and energy intake did not differ between conditions (P-condition > 0.05). CONCLUSIONS: One-night exposure to NH reduced PNS activity, increased HR and RMR, and had no impact on energy intake or appetite when compared with NN exposure. This trial is registered at https://clinicaltrials.gov/ as NCT04151927.