This is one of a series of posts on the science of the Mayo Everest expedition. This is from Amine Issa, Ph.D. on the mountain, with additional comment from Mayo endocrinologist and obesity specialist James Levine, M.D., Ph.D.
The good news is that you tend to lose weight at altitude... but it’s not as simple as you may think. For most people, six hours a day of hiking means an increase in energy expenditure. Weight loss through more calories burned doesn't sound so bad right? However, muscle is broken down to meet increasing energy demands, meaning you will lose a lot more than just your padding. It gets more complicated when you consider that low oxygen conditions force your body to reroute nutrients and blood primarily to sustain your vital functions. This hampers the molecular mechanisms by which your body produces new proteins effectively making it harder to build muscle after breakdown. This altered protein production is evident in the decreased hair and nail growth seen at high altitude. Other biochemical mediators may also cause an increased breakdown of protein, even without heavy exercise.
The rerouting of blood flow to sustain vital functions under hypoxic conditions also affects the digestion of food. Stomach cramps begin to manifest and are followed shortly after by nausea and sometime vomiting, and diarrhea. Many people will actually eat less at altitude, despite being relatively active. This lack of appetite, or acute anorexia, along with the other GI issues contributes to the weight loss experienced at altitude. However there is research that shows that even under standard caloric intake at sea level, hypoxic conditions still cause weight loss. For our expedition we will be using doubly labeled water, a gold standard for measuring energy expenditure, and energy expenditure monitoring devices to measure metabolic changes that may be associated with dietary changes and weight loss. By correlating this data with physiological data gathered during the climb, we will attempt to form a more comprehensive understanding of weight loss and energy expenditure changes that happen at altitude.
Dr. Levine adds: "I emailed Dr Johnson to find out how he is doing on Everest: "Tired, puffing hard", he replied. Dr Johnson's struggle on Everest is no different than any of my patients battling with their weight. Every day is a mountain of exhausting challenges. Although Dr Johnson is burning more calories, he will need to eat more - otherwise he will be tired and lose energy. So too with my patients - they eat to have enough energy to sustain three jobs and their families. Many eat from stress and loneliness. Many of my patients feel as if they are climbing on a mountain alone. However, I would like my patient to understand that, like Dr Johnson, she has a team to support her - her friends that care, at Mayo Clinic. My message to my patient is the same as to Dr Johnson - Keeping going!"