Here's a possible future diet tip: Move to a mountaintop.
In a recent study, obese individuals who spent time at a mountain facility at high altitudes lost weight without going on a diet. And they kept the pounds off for at least four weeks once they returned to normal altitudes.
The researchers suspect part of the weight loss can be attributed to the thin air, which may have decreased participants' appetites and increased their metabolism, meaning they burned more calories sans a workout. While at high altitudes, the obese subjects also showed an increase in levels of leptin, a hormone that when present can make one feel full.
But don't head for the hills just yet — these findings are very preliminary and were only tested in a small sample of people. Further research is needed to confirm the weight-loss effect, and understand why it may occur.
The study is detailed in the Feb. 4 issue of the journal Obesity.
Previous research has found that people tend to lose weight at high altitudes. But most of these studies were done in athletes and hikers who engaged in lots of physical activity.
But would the same effect hold true for obese subjects who were relatively sedentary?
To find out, Dr. Florian Lippl, of Ludwig Maximilians University in Munich, Germany, and his colleagues enrolled 20 obese male participants, with an average weight of 230 pounds (105 kg). They monitored the subjects for one week at low altitudes, looking at what they ate, and how much they walked. Then, the participants spent two weeks in an air-conditioned research facility, located on a mountain at about 8,700 feet (2,650 m) above sea level.
The participants had no restrictions in what they could eat, but they weren't allowed to exercise rigorously. After their stay, the subjects were brought down to normal altitude, and followed up for four weeks.
On average, the participants lost about 3.3 pounds (1.5 kg) while at altitude, Lippl said. This decrease might not seem like much, but it was statistically significant compared with the starting weight.
The researchers think some of the loss can be explained by the fact that the subjects naturally ate less on the mountain, cutting back by 734 calories per day on average.
But a change in diet alone couldn't account for all of the weight loss. The researchers think some of the decrease had to do with a bump in metabolism. On average, the participants' metabolism increased, meaning their bodies burned more calories at rest, without requiring extra movement.
The hunger hormone
In the case of this study, there may be a physiological reason why the participants ate less.
The researchers measured levels of a hormone called leptin, which plays a role in controlling appetite. An increase in your leptin levels means you feel full, while a decrease makes you hungry. Since the obese subjects showed a general increase in there leptin levels at altitude, the researchers say this "hunger hormone" could have been a factor.
Though Lippl and colleagues aren't sure why leptin levels increased on the mountain, they speculate the thin air may have something to do with it. Studies have shown that when human cells are put in a low-oxygen environment (similar to the air at high altitude) they produce more leptin.
Holidays in the mountains
Interestingly, the participants maintained their reduced weight after they had returned to normal altitude and stayed there for four weeks, a finding the researchers did not expect.
But the subjects walked a little bit more, which may have helped keep off the pounds. The researchers aren't sure about the cause of this extra activity, but they think it may be related to the high altitude "training effect," the performance boost athletes experience when they train at high altitudes and race closer to sea level, Lippl told LiveScience.
Without the stress of the low-oxygen, mountain environment, the obese patients may have felt fitter, and were able to exert themselves more, Lippl said.
So could future diet regimes involve skiing vacations?
"With a little humor, I tell my patients now, if they want to take holidays, they should think of mountain holidays [rather] than spending their holidays at the sea," Lippl said.
But in seriousness, Lippl says, the study is really a starting point for further research. He plans to do another study involving more participants over a longer period of time to see if mountain stays can help promote long lasting weight loss.