Substrate Utilization, Exercise Performance, and Skeletal Muscle Response to Energy Deficit and Altitude Acclimatization
Condition: Weight Loss; Other Effects of High Altitude
MeSH terms: Altitude Sickness; Weight Loss
Study type: Interventional

Summary: 
      This research will evaluate nutrition requirements for missions at high altitude (i.e. >7800
      feet above sea level) and the information obtained can be used to optimize nutrient content
      specifications for combat rations.

      The objectives are:

        1. Determine whether loss of lean body mass resulting from negative calorie balance over a
           22-d period at high altitude can be prevented by increasing dietary protein intake.

        2. Determine the efficacy of carbohydrate (glucose and fructose) supplementation on aerobic
           exercise performance at sea level, acute exposure to high altitude, and in response to
           22-d period of negative calorie balance at high altitude.

        3. Determine cognitive function, sleep patterns, and behavioral responses to high altitude
           and underfeeding.

        4. Determine appetite and eating behavior in response to high altitude and sustained
           underfeeding.

        5. Examine the effects of high altitude, negative calorie balance, dietary intake
           manipulations on gut health.
    

Detailed description: 
      Twenty-four, normal to overweight (body mass index of 18.5-29.9 kg/m2), physically active
      adult civilians or active duty military personnel will be recruited for the 44-d protocol,
      22-d at sea level and 22-d at high altitude (HA). During the 22-d sea level phase, volunteers
      will receive dietary counseling to maintain baseline weight and consume protein at levels
      consistent with recommendations for periods of low physical activity (1.0 g/kg/d). During the
      22-d at HA, all meals and beverages (water ad libitum) will be prepared and provided to
      volunteers by research staff. Physical activity will be increased at HA and calorie intake
      will be reduced 40% to create a state of negative calorie balance.

      Changes in total body, lean body, and fat mass will be assessed at sea level and after a 22-d
      energy deficit at HA. Regulation of muscle mass will be assessed using stable isotope
      methodology, muscle biopsies, and various molecular techniques, to directly measure muscle
      protein synthesis, whole body protein balance, and the cellular mechanisms that regulate
      these processes. Furthermore, exercise testing, substrate oxidation rates, and expired carbon
      dioxide labeled with the stable isotope of carbon dioxide (one extra neutron) will be used to
      assess total, exogenous, and endogenous carbohydrate oxidation and performance capacity.

      A comprehensive cognitive/behavioral test battery will be performed at sea level and HA.
      Sleep will be assessed by actigraphy. Eating behavior and appetite will be assessed at sea
      level, acute HA, and after the 22-d energy deficit at HA using validated measures. Gut health
      will be assessed using sugar absorption tests and the bacterial composition of the gut will
      be characterized using advanced molecular techniques.
    

Intervention name(s): Standard pro; High pro; carbo bev; placebo bev
Intervention type(s): Other; Other; Other; Other
Intervention description(s): Volunteers will receive dietary protein at 1.0 ± 0.2 g/kg/d.; Volunteers will receive dietary protein at 2.0 ± 0.2 g/kg/d.; During aerobic performance testing, volunteers will receive a beverage containing 80 g glucose + 65 g fructose consumed at a rate providing ~1.8 g carbohydrate/min.; During aerobic performance testing, volunteers will receive a volume and flavor-matched, non-nutritive placebo beverage.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Prevention