Bears' Hibernation is Linked to Unusual, Major Changes in Their Gut Microbes

Each year, bears hibernate for the winter. They gorge themselves on food to pack on fat, but somehow avoid health consequences. Now, scientists have found that the bears' shifting metabolic status is associated with significant changes in their gut microbes.

"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," said Fredrik Backhed, one of the researchers, in a news release.

The composition of gut microbiota can influence the amount of energy harvested from the diet. In fact, microbiota shifts in people who are obese and in those with type 2 diabetes.

In this latest study, the researchers collected fecal samples from wild bears during hibernation and in the active period. Then, the researchers analyzed the microbes living within these sample. The scientists found reduced diversity in the hibernation microbiota. The scientists also saw changes in several metabolites involved in lipid metabolism, including triglycerides, cholesterol, and bile acids.

In order to further explore whether changes in the microbiota might drive a shift in metabolism, the researchers transferred the bears' summer and winter microbiota into germ-free mice. Mice with the winter microbiota showed greater weight and fat gain. However, there were no differences in their glucose metabolism.

While it's too early to say, the findings in bears might suggest new strategies for managing obesity in humans. They could point to therapeutic targets that could help people in the future.

The findings are published in the journal Cell Reports.

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