Geographic Variation of Human Gut Microbes Linked to Obesity

Individuals who live in cold, northern latitudes have bacteria in their guts that may predispose them to obesity, concludes a new study by researchers at the University of California, Berkeley, and the University of Arizona, Tucson.

The researchers analyzed gut microbes of more than a thousand people around the world and found those living in northern latitudes had more obesity linked gut bacteria than their southern counterparts. The meta-analyis of six earlier studies was published in the journal Biology Letters, by UC Berkeley graduate student Taichi Suzuki and evolutionary biology professor Michael Worobey of the University of Arizona.

"People think obesity is a bad thing, but maybe in the past getting more fat and more energy from the diet might have been important to survival in cold places. Our gut microbes today might be influenced by our ancestors," said Suzuki. She noted that researchers hypothesize obesity-linked bacteria are better at extracting energy from food. "This suggests that what we call 'healthy microbiota' may differ in different geographic regions."

"This observation is pretty cool, but it is not clear why we are seeing the relationship we do with latitude," Worobey said. "There is something amazing and weird going on with microbiomes."

To Worobey, the results impact the study of evolutionary biology. "Maybe changes to your gut community of bacteria are important for allowing populations to adapt to different environmental conditions in lots of animals, including humans," he said.

"Suzuki used data published in six previous studies, totaling 1,020 people from 23 populations in Africa, Europe, North and South America and Asia. The data on gut microbiomes were essentially censuses of the types and numbers of bacteria and Archaea in people's intestinal track," according to the press release announcing the findings.

Suzuki found that the proportion of Firmicutes increased with latitude and the proportion of Bacteriodetes decreased with latitude, regardless of sex, age, or detection methods.

"Bergmann's rule - that body size increases with latitude for many animals - is a good one and presumed to be an adaptation for dealing with cold environments," said Suzuki's advisor Michael Nachman, professor of integrative biology and director of UC Berkeley's Museum of Vertebrate Zoology. "Whether gut microbes also help explain Bergmann's rule will require experimental tests, but Taichi's discovery adds an intriguing and completely overlooked piece of the puzzle to this otherwise well-studied evolutionary pattern."