Previous studies investigating the effects of high altitude (1500 – 3500 m) exposure on energy balance demonstrate various physiological adaptations that support negative energy balance, such as increases in resting metabolic rate and reductions in energy intake and appetite. Normobaric hypoxic exposure using a hypoxic tent system at sea level may provide a more feasible alternative to induce negative energy balance than travel to high altitude. Previous studies investigating the effects of normobaric hypoxic exposure on determinants and modulators of energy balance provide conflicting results, likely due to differences in study design and methodology. The objective of this randomized, single-blind, crossover pilot study was to investigate the effects of passive (i.e., no exercise intervention), one-night normobaric hypoxic (NH) exposure on energy intake, appetite, and food preferences in healthy, normal weight individuals. We hypothesized that one-night of NH exposure would result in reduced energy intake at an acute ad libitum buffet meal and for the following 24-h, decreased appetite, and increased consumption of sweet food items compared to a one-night exposure to normobaric normoxic (NN) conditions. Participants (n = 20, age = 20 – 45 yrs, BMI = 18.5 – 24.9 kg/m2) were recruited to sleep one night (8-h) in NH conditions (~15% oxygen; achieved with nitrogen dilution, equivalent to ~2,590 m elevation) and another night (8-h) in NN conditions (control, ~20% oxygen; equivalent to ~304 m elevation) with at least a 2-wk wash-out between visits. Study visits for all female participants were scheduled within the first 7-d of their menstrual cycle. Dietary intake was monitored using an automated, self-administered 24-h dietary recall (ASA24®) on the day before, during, and after each visit. Following overnight exposure to NH or NN, participants were given access to an ad-libitum buffet-style breakfast meal designed to assess energy and macronutrient intake and food preferences. Pre-meal (0 min) and postprandial (30, 45, 60, 90, 120 min) subjective appetite ratings were obtained using visual analog scales. This thesis manuscript is an interim analysis of an ongoing study and includes 9 participants (3 males, 6 females). There were no statistically significant treatment differences in appetite, energy intake, or food preferences following the ad-libitum buffet meal. There was a trend (P = 0.11) for a greater gram weight of low-fat sweet foods consumed following NH compared to NN, but this did not coincide with an increase in caloric intake. There was a numerical, but not statistical, trend towards decreased total daily energy intake following NH compared to NN (1732 ± 532 vs. 1914 ± 507 kcal, respectively; P = 0.60). These data may inform subsequent research investigating the effects of chronic (e.g., weeks to months), consecutive overnight exposures to normobaric hypoxia to induce negative energy balance in overweight or obese individuals. Furthermore, this study may demonstrate a novel protocol to quantify food preferences in future nutritional studies. In conclusion, this interim analysis demonstrates the feasibility of measuring energy intake, appetite, and food preferences following a one-night, 8-h exposure to either normobaric hypoxia or normobaric normoxia in healthy, normal weight males and females.
