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.
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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
PREVENTION
Masking
SINGLE
Enrollment
21
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.
US Army Research Institute of Environmental Medicine
Natick, Massachusetts, United States
Change in lean body mass
Time frame: baseline (sea level day 0), prior to altitude exposure (sea level day 20), after ~3 wk energy deficit diet at high altitude (high altitude day 19)
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