Aside from the steep hills they have to climb, there's another reason why people who live in the mountains have fine figures – the air.

According to research by the University of Munich, published in the journal Obesity, fat is much easier to burn off when the air is thin.

A study of 20 men, who had an average body mass index of 34, showed that weight dropped dramatically just by living near the top of Germany's highest mountain, Zugspitze, for a week.

The men made no change to their exercise or eating patterns. What's more, it was found that the weight loss was maintained for four weeks afterwards.

It's thought that the discovery could now lead to new obesity treatments which use tents that mimic the atmosphere of high altitude countries such as Tibet.