No one can work on an empty stomach.
It is old news that warfighters conducting combat operations in mountainous regions such as Afghanistan can experience significant loss of weight and muscle mass. Yet, this loss may not entirely be due to a lack of food or high physical activity levels. Hypoxia, a condition that leads to Acute Mountain Sickness, or AMS, could be playing a major role in muscle loss during high-altitude missions.
For the past 10 years, researchers from the U.S. Army Research Institute of Environmental Medicine, or USARIEM, have conducted a series of underfeeding studies in order to evaluate nutrition requirements needed for working in extreme environments. High altitude — greater than 11,500 feet — had been one of the puzzle pieces that USARIEM’s Military Nutrition Division, or MND, had not yet explored until last summer.
MND researchers conducted a six-week underfeeding study with 17 test volunteers at the Institute’s Maher Memorial Altitude Laboratory, located 14,115 feet above sea level on the Pikes Peak summit in Colorado. According to Dr. Stefan Pasiakos, the study’s principal investigator, the purpose was to better understand nutrition requirements for high-altitude missions and to provide evidence that can be used to optimize the combat ration. Specifically, the Modular Operational Ration Enhancement, or MORE, a food ration the U.S. Natick Soldier Research, Development and Engineering Center’s Combat Feeding Directorate developed to provide warfighters additional calories during strenuous high-altitude missions.
“The most consistent issue we see during operations is that warfighters are not eating enough, which causes a negative calorie balance and, ultimately, a loss of muscle mass,” Pasiakos said. “USARIEM researchers want to ensure that warfighters are consuming the right blend of macronutrients, particularly carbohydrates and protein, during periods of negative calorie balance to protect against muscle wasting, physical performance declines and cognitive deterioration — in this case, during high-altitude missions.”
Researchers executed a highly controlled diet and exercise intervention at the Pikes Peak lab. They assessed body composition, muscle protein and carbohydrate metabolism measurements, appetite, gut microbiome, exercise and cognitive performance at sea level, during and after 21 days of high-altitude exposure.
According to Pasiakos, this is not the first time researchers have studied the effects of hypoxia and underfeeding, but it is the first comprehensive and systematic approach to identify how hypoxia elicits muscle wasting and how a warfighter’s diet during high-altitude missions can either contribute to muscle loss or help protect warfighter muscle and performance.
What may explain the loss of body weight and muscle during high-altitude missions?
“Hypoxia diminishes the ability to deliver oxygen to the body, so metabolism ramps up because the body still needs the same amount of oxygen to function,” Pasiakos said. “Warfighters need to eat more to maintain body weight. But appetite is also suppressed. While these symptoms improve as warfighters acclimatize to high altitude, the higher amount of calories needed versus the lower amount of calories consumed is going to cause warfighters to lose weight. Warfighters’ abilities to maintain muscle mass, prevent injury and sustain physical and cognitive performance are at greater risk of being compromised.”
Volunteers ate either a standard-protein diet or a higher-protein diet consistent with recommendations for periods of high physical activity to see how well they maintained their muscle mass when losing weight. Researchers also fed volunteers either a multi-carbohydrate blended drink or a placebo to test how efficiently the volunteers burned carbohydrates during endurance exercise and how fast they were able to complete a two-mile run.
Pasiakos said that while the volunteers went through the stress of being underfed and performed high levels of physical activity, they were monitored by “research staff, with over 100 years of combined physiology research at high altitude.”
“The practical experience and can-do attitude of our staff enabled the team to tightly control physical activity and diet and execute complex experiments throughout this six-week study,” Pasiakos said.
For the price of underfeeding the test volunteers, warfighters could be better fed during future missions.
“The knowledge learned from this study will improve Soldier readiness by advancing our understanding of the nutritional requirements for warfighters working in extreme high-altitude environments,” said Pasiakos. “Recommending dietary changes to the ration composition is one method to help prevent muscle loss and maintain physical and mental performance during high-altitude stress.”
Pasiakos said that researchers are currently “digesting the results.” He will share the study outcomes with the ration developer to optimize the dietary composition of future combat rations.
“Nutrition recommendations for athletic performance are available, but they do not necessarily apply or are practical for warfighters operating in environmental extremes, due to limited access to foods or mission constraints on eating,” Pasiakos said. “It is our job to define nutrition requirements and identify solutions specific to our warfighters under the multiple circumstances they operate in. This study is expected to advance our understanding of how to best feed warfighters during high-altitude missions.”