Carbs Are Key to Survival at High Altitude
New evidence of differences in energy metabolism between high- and low-altitude native mammals.
-- by Alexia Severson
Loading up on carbohydrates may be the key to surviving in harsh, high-altitude environments, according to a new study conducted with collaborators from the Universidad Peruana Cayetano Heredia and reported online in Current Biology, a Cell Press publication.
According to researchers, this study provides the first compelling evidence of a clear difference in energy metabolism between high- and low-altitude native mammals. And while the study was conducted on mice living in the high-altitude, oxygen-starved environment of the Andean mountains, this research may also apply to humans and other mammals.
At an altitude of about 4,000 meters, every breath of air contains about 40 percent less oxygen than it would at sea level. Because carbs can supply 15 percent more energy for the same amount of oxygen in comparison to fats, a diet packed with carbohydrates is the most logical in these conditions.
Researchers said it has been known for many years that burning carbohydrates uses less oxygen to produce the same amount of energy as other available fuels. The idea that high-altitude environments should favor carbohydrate metabolism was proposed almost 30 years ago, but it has never been put to the test until now.
The Expert Take
Based on this theory, study author Grant McClelland and his colleague Marie-Pierre Schippers of McMaster University predicted that high-altitude native animals should rely to a greater extent on carbs for exercise to take advantage of this economical use of oxygen.
“We have shown one way these mice may be able to survive in this harsh environment is by squeezing out extra energy from the oxygen they have available,” he said. “Why don't all mammals use this strategy? Probably because mammals, including humans, store carbs in very low amounts—about 1 percent of the total available energy for metabolism.”
According to McClelland, this strategy may explain why these high-altitude mice are the only mammals that have been found to change the mix of fuels used during exercise. It may also hold strong implications for future research.
“Global climate change has seen altitudinal distributions of some animals change as they seek cooler environments,” he said. “Understanding adaptations to high altitude may help predict the success of high altitude colonization by lowland native animals.”
Source and Method
This study takes a multispecies approach, using four native species of male mice living at different altitudes: two from the Peruvian Andes and two found at sea level. McClelland and Schippers teamed up with scientists in Peru who had done previous work on the ecology of the leaf-eared mouse group (genus Phyllotis).
All mice were captured with Sherman traps and transported to the animal facility of the Universidad Peruana Cayetano Heredia (UPCH) in Lima, Peru. After at least six weeks in captivity at sea level, researchers determined the aerobic capacity of all mice and then performed the following measurements in a random order: rates of O2 consumption (VO2) and CO2 production (VCO2), at rest, at a target exercise intensity of 75 percent of each individual VO2max and time to fatigue at a speed of 12 meters per minute.
According to McClelland, because this study shows one of "nature's solutions" to low oxygen, it may hold promise for future interventions of human diseases that restrict tissue oxygen delivery.
This research also gives a better understanding of mammals in general and the way in which they adapt to climate change and high altitude conditions.
In a study published in 2010 in Progress in Cardiovascular Diseases, researchers determined that high-altitude provides a unique opportunity to study fundamental mechanisms of diseases. Based on previous research and observations, authors of this study shed light on conditions and diseases that mimic the low oxygen content of the atmosphere at high altitude conditions.
Another study published in 2007 in BMJ revealed that soccer teams from high altitude countries have a significant advantage over lowland teams unable to adjust to high altitude conditions. At high altitude, researchers found that lack of oxygen (hypoxia), cold, and dehydration can lead to altitude sickness, breathlessness, headaches, nausea, dizziness, or fatigue. Therefore, activities such as football can make symptoms worse and prevent players from performing their best.
In a slightly different approach, research published in The American Journal of Physiology—Regulatory, Integrative and Comparative Physiology in 2009 found that pregnant women who are indigenous to the Andes Mountains deliver more blood and oxygen to their fetuses at high altitude than women of European descent. Additionally, babies of Andean descent born at high altitude were found to weigh more than European babies born at high altitude. Among several other findings, researchers determined that the greater the mother's Andean heritage, the greater the oxygen delivery to the fetus.