Beijing: Scientists have uncovered the key reason why giant pandas are able to survive solely on a diet of bamboo.

The researchers found that pandas get by on shoots and leaves because they expend extremely small amounts of energy. A typical adult panda burns up about 38 percent of the calories used by other, similarly sized animals. The scientists found the bears’ slow-moving ways were linked to low levels of thyroid hormones.

Scientists have long been intrigued as to how the black and white mammals are able to live exclusively on hard-to-digest bamboo, since their stomachs still retain the gut bacteria of the omnivorous creatures they evolved from. This new analysis sheds light on the mystery. The researchers looked at the daily energy expenditure of five captive pandas and three living in the wild. They found that the creatures used around 38% of the predicted value for mammals of their size.–BBC

This compares to slow-moving koalas, which use around 69 percent of the energy normal for similarly sized animals. The most direct comparison with the pandas’ laid-back ways was three-toed sloths, which have a similarly minimal energy consumption for their size.

When the researchers measured the panda’s rates of movement they found they were only active 49 percent of the time, and when they did move, their average speed was a less-than-blistering 20 metres per hour. “Pandas save a lot of energy by being frugal with the energy they spend on physical activity,” said Prof John Speakman, from the University of Aberdeen and Chinese Academy of Sciences, one of the study’s lead authors.

“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 thyroid hormones, which was linked to a genetic mutation in the thyroid hormone synthesis pathway that is unique to the panda.” These hormone levels were the equivalent to those found in hibernating black bears.