In the February 4, 2010 publication of the journal Obesity, German medical scientists reported that 20 overweight and middle-aged men living in Munich who were subsequently moved to a German mountain resort ( Zugspitze) at 8,700 feet lost an average of about 3½ pounds in a week
During the seven days they spend at high altitude the men were allowed to eat whatever they wished and they were prevented from performing any strenuous physical activity. Not only did they lose 3½ pounds while at the high altitude resort, but, followup measurements performed a month after the men returned to Munich showed that they remained about 2 pounds lighter than before the study began.
The data obtained from the study showed that the men ate less at high altitude and burned more calories, even without exercise.
What does all this mean?
It's hard to draw firm conclusions. The study was uncontrolled, meaning that 20 similar men were not followed at the same time at low altitude and thus it is possible that the men ate less simply because they knew they were in a weight control study. Still, their reduced consumption doesn't account for all the weight loss and since exercise was carefully limited, neither does it. It might be that the extra calories were simply burned off from heavier and more rapid breathing--a natural protective reflex at high altitude. Still, the results are interesting and warrant further study.
Lippl, F.J., Obesity, published online Feb. 4, 2010