Giant pandas are able to live on a diet nearly exclusively consisting of bamboo, a food that contains few nutrients, which has long puzzled biologists.

Researchers have recently discovered that the massive creatures are able to do this because they evolved to use little energy. In short, pandas are able to live on bamboo because they are lazy.

Pandas were studied by researchers, both in the wild and in captivity. Investigators recorded the daily energy expenditure (DEE) of eight pandas, three of which lived in the wild. The study revealed that giant pandas do not move around much, allowing them to spend their days eating.

Even in the wild, pandas only spend about half their days being active, while those in captivity were in motion just one-third of the time. This is among the lowest level of physical activity ever recorded in an animal as large as these creatures. These animals expend roughly half the energy of a human being of the same weight.

Other factors, including thyroid hormone levels similar to a black bear during hibernation as well as small brains, kidneys and livers, also allow pandas to subsist on the tough plant.

"However, it is not only their low activity that contributes to their low metabolism; the metabolic rate of an active panda is still lower than a completely stationary human. We found that their low metabolism is correlated with very low levels of their thyroid hormones, which was linked to a genetic mutation in the thyroid hormone synthesis pathway that is unique to the panda," John Speakman of the University of Aberdeen and Chinese Academy of Sciences said.

Low metabolic rates often pose a problem of heating the body in other species. A thick coating of fur allows the pandas to maintain a high body temperature, researchers found. Many other animals require regular hibernation to lower energy demands of their bodies.

Pandas once ate meat as well as plants but evolved to eat a diet consisting nearly exclusively of bamboo. However, their digestive systems are still designed to consume animal products, which means pandas need to eat as much as 50 pounds of bamboo each day to sustain their survival. The creatures do not move often, and when they do, movement is slow, saving energy.

"It is my long-time dream to accomplish this fascinating study to understand how low the giant panda metabolism would be, and why the giant pandas can survive on their specialised and low-quality bamboo diet. Finally we have done it!" Fuwen Wei of the Chinese Academy of Sciences told the press.

Study of how laziness helps pandas to survive on bamboo was published in the journal Science.

Photo: Will Sowards | Flickr