Gorging oneself on high-calorie food to pack on fat only to fall asleep for a few months and have it all melt away isn’t the latest diet fad (at least not yet), but it is a regular part of life for bears as they prepare to hibernate for the winter. Yet, despite the rapid weight gain, the animals somehow avoid the health consequences so often associated with obesity in humans.
Researchers at the University of Gothenburg in Sweden have published results from a study wherein they show that bears' shifting metabolic status is associated with significant changes in their gut microbes. The researchers were particularly surprised by the discovery that the bears' summer gut microbiota included bacteria that take in more energy from the diet.
“The restructuring of the microbiota into a more avid energy harvester during summer, which potentially contributes to the increased adiposity gain without impairing glucose metabolism, is quite striking,” explained senior study author Fredrik Bäckhed, Ph.D., professor at The Wallenberg Laboratory for Cardiovascular and Metabolic Research within the University of Gothenburg.
The findings from this study were published recently in Cell Reports through an article entitled “The Gut Microbiota Modulates Energy Metabolism in the Hibernating Brown Bear Ursus arctos.”
Previous work done in Dr. Bäckhed’s laboratory showed that the composition of gut microbiota can influence the amount of energy harvested from the diet, and more recently the investigators found that the microbiota also shifts in people who are obese and in those with type 2 diabetes. This led the team to hypothesize whether changes to the microbiota might also be important in hibernating brown bears in the wild.
“We analyzed the microbiota of free-ranging brown bears during their active phase and hibernation. Compared to the active phase, hibernation microbiota had reduced diversity, reduced levels of Firmicutes and Actinobacteria, and increased levels of Bacteroidetes,” the authors wrote. “Several metabolites involved in lipid metabolism, including triglycerides, cholesterol, and bile acids were also affected by hibernation.”
Dr. Bäckhed’s team took their investigation a step further by exploring whether the changes in the bears' microbiota was driving the shift in metabolism by transferring the bears' summer and winter microbiota into mice.
“Transplantation of the bear microbiota from summer and winter to germ-free mice transferred some of the seasonal metabolic features and demonstrated that the summer microbiota promoted adiposity without impairing glucose tolerance, suggesting that seasonal variation in the microbiota may contribute to host energy metabolism in the hibernating brown bear,” described the authors.
The researchers were encouraged by their findings and believe it's possible that the findings in bears might suggest new strategies for managing obesity in humans; however, Dr. Bäckhed urged caution about over-interpreting the study results.
“I think it's too early [to say], as I consider this being very basic science,” Dr. Bäckhed concluded. “However, if we learn more about which bacteria and the functions that promote and/or protect against obesity [in hibernating bears], we may identify new potential therapeutic targets.”