Why are pandas so chubby if their diet consists only of bamboo?

Giant pandas are the only species in the bear family that feeds entirely on plant food. Scientists have long been interested in how these animals endure low temperatures without hibernating or migrating to warmer regions. Studies have shown that these black-and-white bears have unique features that allow them to gain weight despite a low-calorie diet. These features are related to Clostridium butyricum bacteria residing in their bodies.

Chinese zoologists have established that these microbes help giant pandas extract more energy from bamboo shoots and store it as fat. This significantly eases the survival of the animals during the winter period when food becomes scarce.

“We have discovered the first case where seasonal changes in the composition of the microflora noticeably affect the appearance of animals. The discovery of these microbes will open new possibilities for developing treatment methods for digestive disorders in pandas and deepen the understanding of the role of microflora in the lives of wild animals,” noted one of the authors of the study, researcher Huang Guangping from the Institute of Zoology of the Chinese Academy of Sciences.

The researchers analyzed samples of the microflora of pandas living in the foothills of the Qinling Mountains, collected in warm and cold seasons. The scientists' interest in these samples was due to the fact that in autumn and winter, pandas begin to feed exclusively on bamboo leaves, while in spring and summer, they prefer more nutritious young shoots of this plant.

Biologists carefully studied whether the composition of the microflora of pandas changes when switching from a more nutritious diet to leaves and back. To do this, they compared microflora samples, isolated key bacteria, and investigated how their introduction into the intestines of mice affected the behavior and vitality of the rodents.

It turned out that in spring and summer, the number of Clostridium butyricum bacteria in the intestines of pandas increased. These microorganisms are capable of breaking down plant sugars, converting them into other organic substances that serve as precursors for fat molecules. This led scientists to think that these microbes contribute to rapid weight gain and energy accumulation in fat tissue during warm weather.

The scientists tested this hypothesis in experiments on mice: biologists transplanted colonies of these bacteria into the intestines of the rodents. Observations showed that rodents with transplanted Clostridium butyricum gained weight significantly faster when there was an excess of calories in their diet. Furthermore, biologists discovered that Clostridium butyricum directly activate the Per2 gene, which is responsible for energy accumulation in fat tissue.

This allows pandas to maximize the efficient use of low-calorie plant biomass and survive during periods when food is extremely scarce. Further research on the microflora of pandas, as Huang Guangping and his colleagues hope, will help identify other microbes that are critically important for the survival of these unique animals.