Scientists through a recent study were successful in knowing that underactive thyroid glands of giant pandas are the key reason behind the animal’s survival on only bamboo.

The American Association for the Advancement of Science reported that stomachs of these bears are not designed to digest the harsh low-nutrient, high-cellulose plants, but they still manage to survive on a diet which consists majorly of bamboos.

Researchers of the study published in the journal Science stated that theirs is the first to report measurements of daily energy expenditure (DEE) in bamboo-munching pandas.

The team for the study studied five captive pandas and three wild pandas. They found that DEE was only 38 % of the average seen in terrestrial mammals of similar body masses.

Researchers for the study used GPS loggers to track the movement of bears, and found pandas are much lazier than their close relatives. Further research on the animal revealed that a panda’s brain, liver, and kidneys are relatively smaller than most other bear species.

The pandas also have thyroid hormone levels that are found to be only a fraction of the mammalian norm, and are comparable to hormone levels seen in hibernating black bears.

The study researchers compared the giant pandas' genome with other mammals, and noted a unique variation on the DUOX2 gene. Researchers said that loss of this gene is linked to underactive thyroids in humans.

“Taken together, these results suggest that particularly low energy expenditures and thyroid hormone levels enable the carnivorous-looking panda bears to munch on bamboo all day”, said researchers.