Peak of fitness. Spending time on Zugspitze, pictured here, in Germany, appears to spur weight loss.

Christian Nawroth

Can Thin Mountain Air Make You Slim?

Looking for a new weight loss plan? Try living on top of a mountain. Twenty obese men spent a week near the top of Germany's highest peak and saw their metabolism speed up, their appetite diminish, and more pounds melt off than they likely would have had they stayed at home, a new study reports. However, the study lacked a control group, so firm conclusions are tough to draw, other researchers say.

Mountain air contains less oxygen than air at lower altitudes, so breathing it causes the heart to beat faster and the body to burn more energy. A handful of studies have found that athletes training at high altitudes tend to lose weight. Gastroenterologist Florian Lippl of the University Hospital of Ludwig-Maximilians-University Munich in Germany wondered how the mountain air would affect obese individuals if they weren't doing any more physical activity than usual. "We know from our outpatient unit that it's hard to motivate our obese patients" to exercise, says Lippl. "We thought if we bring them up there, the higher metabolic rate will do most of the work for them."

Lippl and his colleagues invited 20 obese men to an environmental research station about 300 meters below the summit of Zugspitze, a mountain near the Austrian border. This was no hiking expedition. The subjects reached the outpost at 2650 meters altitude almost effortlessly, by cog railway and cable car, and once there could only take the same number of steps each day that they were accustomed to taking at home, as monitored with a pedometer. They were allowed to eat as much as they liked. The men also gave blood so that researchers could test for hormones linked to appetite and obesity, such as leptin and ghrelin.

At the end of the week, the men, whose mean weight starting out was 105 kilograms, had lost on average about 1.5 kg, the researchers report 4 February in Obesity. The men's blood pressure also dropped, which the researchers attributed to weight lost. In addition, leptin levels rose. Normally, those levels fall when food intake decreases, but in this case Lippl attributes the change to the thin air.

Exactly what caused the weight loss is uncertain. Loss of appetite is common at higher altitudes, and indeed the men ate significantly less than usual--about 700 calories fewer per day, or a bit over 2000 calories total. Lippl also notes that because their consumption was being monitored, they may have been more self-conscious about what they ate. Regardless, eating less accounts for just 1 kg of the 1.5 kg lost, says Lippl. Lippl thinks the increased metabolic rate, which was measured, also contributed to weight loss but cannot separate the different effects with the given data.

The work is preliminary but intriguing, says Richard Bergman, a physiologist at the University of Southern California in Los Angeles and editor of Obesity. He notes that Colorado, with many residents living at high altitudes, is the least obese state in the United States, and this paper "might give us insight as to why."

Appetite loss at high altitudes could certainly be key, notes Damian Bailey, a physiologist at the University of Glamorgan, Pontypridd, in the United Kingdom who himself recently lost 11 kg during a 3-month expedition to the Andes in Chile. Bailey agrees Lippl's findings are interesting but laments the study's lack of a control group staying at low altitudes.

Unfortunately, for the average person there's no treatment that can mimic living at high altitude, says Lippl. The only alternative is a hypobaric chamber, which exposes subjects to low oxygen and isn't practical as a therapy. For now, he says, half-jokingly, "if obese people plan their holidays, they might not go to the sea, but maybe to the mountains."