We are so used to seeing the iconic black and white panda bears clutching skinny sticks of bamboo that it is hard to imagine them eating anything else. Fact is, their diet does not deviate much from this perception – by a mere one percent, to be precise.

Pandas, which conversely, are as beloved as they are endangered, are the only one of the world's eight bear species to largely adhere to vegetarian principles. But they could, like their grizzly cousins, just as easily be devouring smaller animals for breakfast, lunch and dinner.

Their systems are equipped to deal with a carnivorous lifestyle, which would give them the energy they need to survive and thrive with greater ease. But then again, they make eating bamboo look like such fun.

Scientists have long wondered at how the endangered species manages to get by on a foodstuff that is both notoriously low in nutrients and hard to digest. And now it seems they have found the answer.

Take it lying down

In brief, the bears take a sedentary approach to life. A team of researchers, led by Fuwen Wei of the Chinese Academy of Sciences' Institute of Zoology in Beijing studied pandas both in the wild and captivity, and found them to be masters in the art of lounging.

The wild animals they observed were found to rest for more than half of each day, moving at an average rate of 20 meters an hour. Those in captivity were even lazier. The researchers, who published their findings in the #link:http://www.sciencemag.org/content/349/6244/171 :Science# journal also believe the relatively small size of the bears' internal organs aids their survival.

"These reduced organ sizes likely contribute to their low energy demands," Wei said.

Sluggish metabolism

But that is not all. Even when they are active, pandas have a slower metabolic rate than a completely stationary human.

"Giant pandas achieved this low metabolism through a suite of morphological, behavioral, physiological and genetic adaptations during their long evolutionary history," Wei continued.

That goes some way to explaining why the pandas observed for the study only expend 38 percent as much energy as other animals of a similar size. That puts them on a par with the three-toed sloth on the exertion scale.

That said, an adult panda needs to consume between 12 and 38 kilograms of bamboo a day. That implies as many as 15 hours of spent eating. At that rate, is it any wonder they don't have much energy for anything else?