Effects of Overnight Low Oxygen Exposure on Energy Balance

Weight loss is a common factor reported in lowlanders traveling to high altitudes. Although the exact cause is unknown, studies have shown that weight loss at high altitude is associated with the amount of time and severity of the altitude exposure. Upon arrival to high altitude (≥ 5000 feet), numerous physiological adaptations occur that may promote weight loss, such as increased energy expenditure and reduced appetite. The breadth of current altitude research is limited by the logistical and monetary constraints of traveling to remote locations or access to an altitude chamber. A more logistically feasible alternative is the simulation of low oxygen conditions at sea level, using a commercially available tent and generator system to reduce ambient oxygen concentrations. The current research study will evaluate changes in resting metabolic rate, appetite, and heart rate variability following overnight exposure (8 h/night) to normobaric hypoxia (NH) or normobaric normoxic (NN). In randomized order, participants will sleep one night in NH conditions ( 15% oxygen; achieved with nitrogen dilution, equivalent to 8500 feet elevation) and another night in NN (control) conditions ( 20% oxygen; achieved with nitrogen dilution, equivalent to 1000 feet elevation). In the morning, following NH or NN exposure, resting metabolic rate will be measured using indirect calorimetry, appetite using an ad libitum buffet meal protocol, and heart rate variability by electrocardiogram. It is hypothesized that exposure to overnight NH will result in increased resting metabolic rate, decreased appetite, and decreased heart rate variability.