Giant pandas are the new couch potatoes of the animal world, according to a study Thursday that found the bears are just as sluggish as slow-moving sloths.
Researchers in China tracked five captive pandas and three wild ones for the study published in the journal Science.
They found that pandas are far less active than other bears, and expended just 38 percent as much daily energy as the average among other land animals of their size.
"The daily energy expenditure values for giant pandas are substantially lower than those for koalas, for example, and more akin to those of three-toed sloths," said the study.
Panda brains, livers and kidneys were also found to be smaller than the organs seen in other bears.
Their thyroid hormone levels "are only a fraction of the mammalian norm—comparable to a hibernating black bear's hormone levels," added the study, which identified a gene variation in pandas that matches one seen in humans with underactive thyroids.
Thyroid hormones are important for regulating body weight and energy, and low levels can lead to sluggishness.
Previous research has shown that pandas' stomachs are not well-suited for their bamboo diet.
But taken together, the bears' small organs, genetic adaptations and take-it-easy attitude allow them to survive on bamboo, concluded the study.
Pandas' natural habitat lies in mountainous southwestern China.
China has about 1,600 pandas living in the wild and another 300 held in captivity.
Explore further: China's latest survey finds increase in wild giant pandas
Low daily energy expenditure and metabolic rate in the bamboo-eating giant panda, www.sciencemag.org/lookup/doi/ … 1126/science.aab2413