Why Pandas Eat So Much Bamboo: They Can Bear-ly Digest It

Giant panda Wei Wei sticks out his tongue during snowfall at a zoo in Wuhan, China. REUTERS / China Daily

If you're a panda bear, there's one thing you do a lot: eat bamboo. These creatures actually spend up to 14 hours daily eating as much as 27 pounds of the plant.

New research gives a clue as to why: They aren't very good at digesting it.

A paper published today in the journal mBio shows that pandas have gut microbes more similar to carnivores and omnivores than vegetarians. In fact, the animals lack the types of bacteria known for breaking down cellulose, the component of plant cell walls that make leaves and plant material difficult for other omnivores, like humans, to break down. Pandas can digest only about 17 percent of what they consume, the scientists calculated.

"This result is unexpected and quite interesting, because it implies the giant panda's gut microbiota may not have well adapted to its unique diet and places pandas at an evolutionary dilemma," said study co-author Xiaoyan Pang, a researcher at Shanghai Jiao Tong University, in a statement.

The study notes that the bears evolved from omnivorous ancestors but likely began to specialize in bamboo-chomping 7 million years ago. But in that time, they haven't evolved to become efficient at breaking down cellulose. As a result, the panda's stomach and intestinal system are more similar to a carnivore than a vegetarian.

"The animals also do not have the genes for plant-digesting enzymes in their own genome," said lead author Zhihe Zhang, director of the Chengdu Research Base of Giant Panda Breeding in China. This, he says, "may have increased their risk for extinction."