In addition to a lack of oxygen, there may be another reason it’s called thin air--researchers have been exploring the relationship between weight loss and high altitudes. Last year, a study published in the International Journal of Obesity found a strong association between altitude and obesity prevalence within the United States. Using data for over 400,000 people, researchers found Americans living closest to sea level were four to five times more likely to be obese, compared to people who live well above sea level in Colorado.
Everyone knows the problems with correlation and causation:
The study was more complex than just correlation--it used statistical analysis to control for factors such as activity level, temperature, and urbanization. Still, the issue was something the researchers recognized--as one of the study’s contributors, Dr Jameson Voss, noted, “While it is always important to remember correlation does not prove causation, in this case, we already know hypoxia causes anorexia and weight loss based on well controlled interventional data.”
What causes weight loss at high altitudes? Many studies have looked at climbers at high altitudes and, expectedly, increased energy expenditure due to increased physical activity can contribute to some of their weight loss. Exercise at high altitudes doesn’t fully explain weight loss, though. Studies have indicated that decreased energy consumption due to lack of appetite is one of the more significant causes of weight loss during high altitude exposure. Researchers conducted a study in a hypobaric chamber that simulated a 40 day ascent of Mount Everest. Despite having ample amounts of palatable food available, participants experienced a loss of appetite, leading to a decrease in caloric intake and subsequent decrease in weight. Because factors such as harsh environmental stressors were omitted and large quantities of appetizing food were provided, the researchers believe the findings suggested that "hypoxia can be sufficient cause for the weight loss and decreased food consumption reported by mountain expeditions at high altitude."
Weight loss can also occur at high altitudes in the absence of exercise. In a preliminary study, a group of obese, mainly sedentary males who spent a week at a moderately high altitude were able to lose weight without exercise. Although the participants were allowed to eat as much as they wanted, they consumed nearly 730 calories less than they typically did at a normal altitude. They also had significantly increased levels of leptin, the protein hormone that plays a role in appetite control and metabolism. In total, the participants lost an average of three pounds and managed to keep two pounds off one month after the study was completed.
The role of leptin in high altitude weight loss has become a bit of a debate because different studies have resulted in different findings. Some show an increase in plasma leptin levels with exposure to high altitude while others demonstrate a decrease with exposure to high altitude. This may be a result of confounding factors but such findings suggest there is even more to be discovered about how leptin and other aspects of conditions at high altitude affect weight loss.
Each year, climbers go up Everest and their weight often goes down.
This happens in the midst of an abundance of food--often food and other supplies make their way up to Everest Base Camp transported by yaks.
While preparing, those attempting the summit can burn an average of 6,000 calories daily. Successful summiters (like these from Malaysia) can be expected to use between 12,000-15,000 calories on summit day.
Climbers often report a preference for carbohydrates at high altitudes. For those attempting the summit at Everest, carb craving can be met by bringing comfort foods from home and also by eating one of the most common dishes served throughout the Himalayas--a traditional dish of lentils and rice.
2 Cups Basmati Rice
4 Cups Water
4 Tablespoons Clarified Butter
1 Onion, chopped
2 Cloves Garlic, minced
1 Tablespoon Ginger, minced
1 Teaspoon Turmeric
¼ Teaspoon Asafetida*
2 Dried Red Chillies
2 Cups Lentils, rinsed
4 Cups Water or Vegetable Broth
Salt and Pepper to taste
Make the rice by bringing water to a boil, adding in the rice and reducing to a low simmer. Cover and cook the rice until it’s firm and tender and the water is fully absorbed (should be about 25 minutes).
To make the lentils, saute onion, garlic and ginger in butter for one minute. Add lentils, spices, chillies and water or broth. Bring to a boil, then reduce heat and simmer, covered, for about 30 minutes until lentils are soft. Serve rice and lentils garnished with achar.
*Asafetida is a spice once described by Harold McGee as “one of the strangest and strongest of all spices” and is commonly found in Indian supermarkets.
Image Credits: xkcd.com, remainder by author.