Pandas enjoy the sweet life

panda eating bamboo

A giant panda’s diet primarily consists of bamboo, which isn’t sweet, so scientists had assumed that pandas lost the ability to taste sweet stuff. But new research shows that the animals can indeed taste sweet sugars.

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Many animals, including humans, have the ability to taste sugar and have it register as “yummy.” Scientists think that sweet receptors help an organism identify plants that are rich in simple sugars and rich in calories. Many carnivores, which eat only or mostly meat, have lost that ability to enjoy sweet things. Cats are the most well-known of the sugar-disdaining creatures, but the group also includes sea lions, fur seals and spotted hyenas.

Giant pandas also belong to the order Carnivora, but they are a bit of an outlier because instead of consuming mostly meat, their diets are mostly bamboo. Like meat, bamboo isn’t sweet, so there doesn’t seem to be a need for a panda to be able to taste the presence of sugar. And so scientists thought that the black-and-white beasts might number among the animals that can’t detect the sweet stuff.

Not so, say Peihua Jiang of the Monell Chemical Senses Center in Philadelphia and colleagues. Pandas can taste all six simple sugars and a couple of artificial ones, the researchers report March 26 in PLOS ONE.

The research team worked with eight giant pandas, ages 3 to 22, over a six-month period at the Shannxi Wild Animal Rescue and Research Center in China. At 9:30 in the morning, a panda would be given a choice of two bowls, one containing a liter of water, and the other holding water laced with a sweetener. Six natural sugars were tested — fructose, galactose, lactose, maltose, glucose and sucrose — as were five artificial sweeteners — acesulfame-K (Sweet One), aspartame (which is in Equal and NutraSweet), sodium cyclamate, neotame and sucralose (Splenda). The panda could drink as much as it wanted from either bowl, after which both were taken away and the animal wasn’t tested again for several days.

The giant pandas preferred the natural-sugar waters over regular water, and they really liked the fructose solutions, lapping up the entire liter of sugar water in every test. The animals also seemed to be able to taste a few of the artificial sweeteners — acesulfame-K, sodium cyclamate and sucralose. They actively avoided neotame, though, when they encountered the sweetener in its highest concentration.

The research team confirmed that the pandas have a working receptor for sweet by taking genes for the receptor from panda DNA and inserting them into cultured human cells. Those cells responded to natural, but not artificial, sugars.

“We found that pandas are strikingly similar to humans and many other mammals in their general preference for sugar plus water over plain water and are also similar in their liking for different types of sugars,” the researchers write.

The researchers then posit a few theories as to why the pandas might have held on to this sweet ability even though they don’t appear to need it:

(1)   There might be a compound in bamboo that pandas perceive as sweet even though humans don’t.

(2)   Pandas might eat sweet foods, such as sugar cane, often enough to maintain the sweet receptors. (The authors, citing the animal’s 90-percent-bamboo diet, dismiss this option.)

(3)   The animals might have held onto the sweet-receptor genes by chance. After all, not all carnivores have lost their ability to taste sweet things. Ferrets are among that group.

(4)   Sweet-taste receptors might have another role in the gut or pancreas in plant-eating animals. Even if the animals don’t consume simple sugars in their foods, those extra functions would still be necessary.

Whatever the reason behind the panda’s preference for sweet, we can be assured more moments of adorableness, watching them munch on frozen fruitsicles and other treats.

Sarah Zielinski is the Editor, Print at Science News Explores. She has a B.A. in biology from Cornell University and an M.A. in journalism from New York University. She writes about ecology, plants and animals.

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