Daily Low Oxygen Exposure and Weight Status

The objective of this single-blind, parallel-arm, randomized clinical trial is to evaluate changes in body weight and composition, assess determinants of energy balance, and measure modulators of energy intake and expenditure, following 8 wk of calorie restriction (CR, -500 kcal/d) in combination with either overnight exposure (8 h/night) to normobaric hypoxia (NH; 15% oxygen, \~8500 ft elevation) or normoxia (NN; 21% oxygen, sea level), using a commercially available, in-home tent system, in adults who are overweight or obese.

The current research study will evaluate changes in body weight and composition, assess determinants of energy balance, and measure modulators of energy intake and expenditure, following 8 wk of calorie restriction (CR, -500 kcal/d) in combination with either overnight exposure to normobaric hypoxia (NH) or normoxia (NN). Participants will be instructed to follow their normal diet but with a 500 kcal/day deficit as advised by a Registered Dietitian. Participants will spend 8 hours/night in a tent, set-up around their bed, in their home, for 8 weeks. Participants sleeping in the hypoxic tent (Hypoxico Inc., New York, NY, commercially available tents: https://hypoxico.com/) will breath \~15% oxygen (achieved with nitrogen dilution, equivalent to \~8500 ft elevation), whereas those in the control tent (Hypoxico Inc.) will breath \~21% oxygen (achieved with nitrogen dilution, equivalent to sea level elevation). Trained research staff will set-up the hypoxic or control tent system in each participant's home on day 0 and will visit the participant's home on days 1, 2, and 3 to check and/or adjust the tent settings. After day 3, research staff will visit the participant's home weekly to check and/or adjust the tent settings. participants will be weighed each morning following an overnight fast and morning void. Participants will come to the laboratory on two separate days for baseline testing (days -1 and 0) and again on two separate days at the end of the study (days 55 and 56) for endpoint testing.

Eligibility Criteria:
Inclusion Criteria:

* Men and women aged 20 - 50 years
* Overweight or obese (BMI between 27.5-34.9 kg/m2)
* Born at altitudes less than 2,100 meters (\~7,000 feet)
* Currently residing in Tallahassee, Florida, or the surrounding area
* Not taking any medication(s) that interfere with metabolism or oxygen delivery/transport for 4 weeks prior to and throughout the entire study (e.g., includes sedatives, sleeping aids, tranquilizers, and/or any medication that depresses ventilation, diuretics, alpha, and beta-blockers).
* Willing to refrain from smoking, vaping, chewing tobacco, and dietary supplement use throughout the entire study
* Willing to have a hypoxic tent set-up in their home and spend 8 consecutive hours per night in the tent for 8 weeks
* Lives with a family member, partner/spouse, or roommate who can hear and respond in the unlikely event that the blood oxygen, air oxygen, or air carbon dioxide monitoring alarm would sound.

Exclusion Criteria:

* Living in areas that are more than 1,200 m (\~4,000 feet), or have traveled to areas that are more than 1,200 m for five days or more within the last 2 months
* Metabolic or cardiovascular abnormalities, gastrointestinal disorders, and any condition that interferes with metabolism or oxygen delivery/transport (e.g., kidney disease, diabetes, cardiovascular disease, etc.)
* Evidence of apnea or other sleeping disorders
* Evidence of prior high-altitude pulmonary edema (HAPE) or high-altitude cerebral edema (HACE) diagnosis
* Diagnosis or family history of sickle cell anemia/trait
* Hematocrit \<42% for males, \<36% for females
* Hemoglobin \<13 g/dL for males, \<12 g/dL for females
* Blood donation within 8 weeks of beginning the study
* Present condition of alcoholism, anabolic steroids, or other substance abuse issues
* Allergies or intolerance to foods included in the standardized and ad libitum meal tests (e.g., lactose intolerance/milk allergy)
* Women who are pregnant, lactating, planning to become pregnant, or who have had an irregular menstrual cycle in the past 6 mo.
* Weight gain or loss \> 10% of body weight during the past 6 months
* Adults unable to consent
* Individuals who are not yet adults (infants, children, teenagers)
* Prisoners