The University of California at Berkeley, reported on a study recently published in the online journal Biology Letters by one of its graduate students, Dr. Taichi Suzuki and University of Arizona evolutionary biology professor, Dr. Michael Worobey. This study, which examined the microbiomes (mix of gut bacteria) of thousands of volunteers worldwide showed that people living in more northern latitudes had a mix of bacteria that have been linked with obesity, whereas those living in more southerly latitudes had a the mix seen more often in individuals of healthy weight.
Dr. Suzuki knew that human and animal body sizes increased as you moved away from the equator. We have previously covered the findings that Firmicutes bacteria tend to be found in higher percentages in obese people whereas Bacteroidetes bacteria are found in higher percentages in thin people. Dr. Suzuki was curious to see whether there were geographical differences in the gut bacteria mix whereby those living further from the equator would have more of the “obese” bacteria than those living closer to it. His analysis confirmed that in fact his suspicion was true! His research found regional differences based on latitude, with more of the Firmicutes bacteria found in the guts of people in the more northerly climates.
Having more fat can be protective against cold and heat loss, which can rob the body of essential energy. Seals and whales are not thin mammals. It makes sense that it would be beneficial in pre-modern times to have a high percentage of bacteria that are very efficient at converting food to energy (and fat) in cold climates. In our modern world, however, fat is considered unhealthy. We now have warm clothing and central heating to protect us from extreme temperatures, and the risks of deadly diseases that go along with obesity are no longer offset by the benefits fat’s insulating properties. Modern health recommendations stress the important of being thin. However, the evolution of our microbiome has not caught up to this modern reality.
You may read more about this fascinating finding here: Geographic variation of human gut microbes tied to obesity