New study exposes panda sweet tooth

In a blind taste test, eight out of eight pandas agree - sugar is delicious.

In a new study, scientists put the panda taste receptors to the test, wondering whether the cuddly critters would even notice the difference between plain water and the sweet stuff.

"Generally speaking, animals that eat plants have a sweet taste receptor because that enables them to detect sugars that are in plants that are sources of calories," explained Gary Beauchamp, director of the Monell Center that carried out the research.

But unlike most herbivores, pandas stick to one plant - bamboo - which is notoriously low on sugar.

So the researchers wondered whether - like many carnivorous animals, including cats - pandas had lost their ability to detect sweetness.

Since carnivores "don't eat plants, don't contact sugars, there's no longer a pressure for them to maintain the sweet receptor functional," Beauchamp said.

The theory was that bamboo-munching pandas, who also don't seem to be exposed to much sugar, might also have lost their ability taste sweet things.

But it turned out pandas, like other herbivores, still have a fine-tuned sweet tooth.

When given two bowls of liquid, one sweetened and one not, the eight pandas universally slurped down the sugary brew.

The researchers tested a variety of sugars, including fructose, glucose, sucrose, lactose, maltose, and galactose. In all cases, the sweet drink was preferred, especially the ones with fructose and sucrose, which humans perceive as the sweetest.

The scientists also used cellular analysis to isolate sweet receptor cells from pandas and were able to show they responded to sugars.

They speculate pandas may hold on to working sweet receptor cells because, beyond the taste factor, they may be used in places like the pancreas and the gut to help with plant digestion.

But if pandas love sweets, why do they only eat bamboo?

In captivity, pandas do enjoy sweet foods - including Washington's newest panda cub Bao Bao, who "is apparently relishing sweet potato as a first food during weaning," said Danielle Reed, one of the authors of the paper published in the journal PLOS ONE on Wednesday.

But pandas also need lots of bamboo, or they get sick. One hypothesis is that the reedy plant provides something necessary, so evolutionary pressure has led them to rely solely on the plant.

Another possibility being tested, Beauchamp said, is that for pandas, bamboo actually tastes like candy.

After all, there is definite evidence different animals experience foods differently - like artificial sweeteners, which, for pandas and many other animals, don't taste sweet.