Just a week at high altitudes can cause sustained weight loss, suggesting that a mountain retreat could be a viable strategy for slimming down.

Overweight, sedentary people who spent a week at an elevation of 8,700 feet lost weight while eating as much as they wanted and doing no exercise. A month after they came back down, they had kept two-thirds of those pounds off. The results appear in the Feb. 4 Obesity.

"What is nice about this paper, is that it clearly demonstrates that there’s a lasting effect of decreased caloric intake, that people eat less even a month after they come out of high altitude," said Massachusetts General Hospital anesthesiologist Kay Leissner, who studies high altitude physiology, but was not involved in the study.

Since a 1957 study, scientists have known that animals lose weight at high altitudes. Mountaineers also shed pounds during expeditions to 12,000 feet or more, though the exertion of climbing a mountain clearly played a role.

But the obese are more likely to suffer severe altitude sickness, in which low oxygen pressure causes dizziness, nausea and more serious problems like edema or heart attacks, Leissner said.

So a team at Ludwig-Maximilians University in Munich wanted to see if the pounds also melted away with a safer, sedentary stay at somewhat lower altitude.

The scientists ferried 20 overweight, middle-aged men by train and cable car to a research station perched 1,000 feet below the peak of Germany's highest mountain, Zugspitze. During the week-long stay, the men could eat and drink as much as they liked and were forbidden from any exercise other than leisurely strolls. The team measured the men's weight, metabolic rate, levels of hunger and satiety hormones before, during, and after their mountain retreat.

After a week up high, the subjects lost an average of 3 pounds. A month later, they were still 2 pounds lighter. The sceintists' data showed this was likely because they ate about 730 calories less at high altitudes than they did at normal elevations. They may have felt less hungry, in part, because levels of leptin, the satiety hormone, surged during the stay, while grehlin, the hunger hormone, remained unchanged. Their metabolic rate also spiked, meaning they burned more calories than they usually did.

A high-altitude weight loss strategy could be viable, though studies have shown peoples' appetites bounce back after about six months at high elevation, Leissner said. "If you could do intermittent periods for one week, then go down, and then go back up, this might actually be helpful."

One limitation of the study, however, is that it didn't show whether the men lost mostly muscle mass, fat, or water weight, Leissner said.

And the study didn't show that the stay at 8,700 feet was actually safe for the participants, University of Geneva exercise physiologist Bengt Kayser said in an e-mail.

New research into why the overweight are prone to heart attacks, diabetes, and other inflammatory diseases, suggest it could be some fat cells grow so rapidly that blood vessel growth can't keep up, and that leads to pockets of oxygen-starved fatty tissue, Kayser said. " This causes local inflammation because immune cells get activated."

If that's the case, then shuttling the overweight to even a moderate altitude may worsen inflammation and increase their chances of heart attack or other serious problems.

"So for the moment one has to remain very careful," Kayser said, "and evaluate the question a few more times before migrating all obese Americans to Colorado!"

Image: Zugspitze, Stephan A./flickr

Citation: "Hypobaric Hypoxia Causes Body Weight Reduction in Obese Subjects," Florian J. Lippl, Sonja Neubauer, Susanne Schipfer, Nicole Lichter, Amanda Tufman, Bärbel Otto, and Rainald Fischer. Obesity, 4 February 2010.

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