Famed for being big and fuzzy, panda bears are one of the cutest animals to roam the planet. Pandas spend their days either sleeping or eating; lots and lots of eating. Bamboo makes up 99% of a giant panda’s diet, of which they consume as much as 20-40 pounds per day. Despite this incredible feat, it still remains a mystery how pandas are able to survive off of bamboo since the tall plant has no fat and contains only about 40 calories and 4 grams of protein in one raw cup—a small amount relative to its size. So how can these massive animals survive on bamboo almost exclusively? The answer may lie in the creature’s efficient ability in managing how they spend their energy, which compared to most animals, is ultimately less.
The Wei group in China recently set out to answer metabolic questions about the giant panda. Your metabolic rate accounts for the number of calories you burn turning the food you eat into energy for your body, and how quickly this process happens. Wei’s group found that on average, giant pandas have a daily energy expenditure (DEE) of approximately 40% of what is expected for an animal this size. This means that pandas use less energy to carry out their day-to-day activities, which the researchers attributed to their inactive, sedentary lifestyle. On top of that, it was also found that the size of key organs (brain, liver, heart and kidneys) which contribute to the body’s total overall metabolic rate were much smaller in the giant panda than in other animals of similar size. Having smaller key organs limits the amount of energy a giant panda can use in maintaining their basic bodily functions. Besides organ size, hormones play a key role in metabolic rates as well. The giant pandas were often found to have lower levels of metabolic hormones in their system compared to other animals.
By having smaller organs, lower levels of metabolic hormones, and being particularly inactive, giant pandas are able to remain ‘giant’ while feeding on an otherwise nutritionally scarce food source. Who ever said physical activity is the key to long life has certainly not met a giant panda.
Nie, Y., Speakman, J., Wu, Q., Zhang, C., Hu, Y., Xia, M., Yan, L., Hambly, C., Wang, L., Wie, W., et al. (2015). Exceptionally low daily energy expenditure in the bamboo-eating giant panda. Science (80-. ). 349, 171–174.