The FSU Nutritional Physiology lab is recruiting individuals who are normal weight (BMI: 18.5-24.9kg/m2), aged 20-45, for a study to evaluate changes in resting metabolic rate, appetite, and heart rate variability following overnight exposure (8 h/night) to reduced environmental oxygen. In randomized order, participants will sleep one night in low oxygen conditions (~15% oxygen; equivalent to ~8500 feet elevation) and another night in normal oxygen (control) conditions (~20% oxygen; equivalent to ~1000 feet elevation). Participants will earn $50 for completing the study as well as dinner and breakfast on overnight visits.