Why Are Pandas So Chubby If They Only Eat Bamboo? Scientists Have Found an Answer.

Pandas, clad in their wooly black and white fur, are known for their cuddly appearance. It’s not usual for their bellies to hang, or their rolls to jiggle, despite feeding exclusively on fibrous bamboo.

So what keeps these bears so thick? 

Scientists found that the answer could lie in the bear’s gut bacteria. 

According to a study published on Jan. 18 in the science journal Cell Report, when bamboo shoot-eating season came around during the spring and summer, the bears’ weight increased. After studying the bears’ poop, the paper’s authors found that there were also higher levels of Clostridium butyricum, a common bacterium also found in humans, during these warmer months. 

The researchers, mainly from the Chinese Academy of Sciences, concluded that a greater presence of this bacteria could help pandas store fat and gain weight, which then helps keep them nourished during winter months when food is scarce. Their vegan diet of pure bamboo, it turns out, is not just because they’re picky eaters.

“Our findings underscore the important role played by the seasonal gut microbiome in the maintenance of the physiological health and fitness of the host,” the researchers said.

Scientists first collected eight wild pandas’ poop in China’s southern Qingling mountains during both leaf-eating season and shoot-eating season. (Bamboo shoots come into season only during the spring and summer.) They then found greater amounts of the bacteria when the panda ate fresh bamboo shoots. 

To determine whether the bacteria help pandas keep the weight on, scientists conducted a fecal transplant and put the panda poop into lab mice. Then, for three weeks, they fed one group of mice only bamboo shoots and another, only bamboo leaves. They afterwards checked whether the group that ate bamboo shoots weighed more. Sure enough, they did. 

Many animals experience a shift in gut bacteria when seasons change, as different kinds of food become available.  

In a 2019 study, a season change was identified in the gut bacteria of bats, which are hibernating animals. Researchers also found a greater variety of bacteria in late summer, when bats have the most diverse diet. In another study of large animals in Kenya, a similar seasonal change in animals’ gut bacteria was observed. 

Some studies have also shown that gut microbes in animals help protect them from adverse environments or, in the pandas’ case, keep them plump.

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