Ranjan Sinha

December 23, 2019

Does Where You Live Affect the Type of Bacteria in Your Gut?

How your microbiome can be influenced by geography

Why don’t polar bears eat penguins?
I’m told it’s a conundrum that regularly pops up in lists of tricky interview questions, easily answered if you know your geography.
Of course polar bears live only in the Arctic, while penguins are only ever found down in Antarctica, safe from the jaws of hungry bears.

We take it for granted that different animal and vegetable species live in different parts of the world.

But what about bacteria?
Could where you live affect the trillions of microorganisms hitching a ride in and on your body?
Well yes, quite a bit actually, and what we know about the geographical diversity of the human microbiome makes for a fascinating story.

Actually perhaps I should begin by saying that scientists’ knowledge on this subject is relatively early-stage.

For example one of the biggest microbiome research projects in the world was the $173 million, five-year Human Microbiome Project.
While it unquestionably generated a huge amount of invaluable data, the project studied just 242 humans, almost all white Americans, 80% of whom came from two cities – Houston and St Louis, about 12 hours drive away from each other on a good day.
Not terribly diverse, then, in almost any way, but a fantastic start.
With a little digging, we can find some truly eye-opening microbiome studies involving more far-flung groups of our planet’s population.
Consider for example the remarkable 2008 research headed by a microbiologist at New York University which studied 12 hunter-gatherers from the Yanomami people in Venezuela, who’d never met anyone outside their own cultural group.
Scientists took advantage of an opportunity to gather stool samples from these incredible individuals when the Venezuelan government helpfully decided they needed to give them medicines and vaccines in case they inadvertently came across illegal miners who might introduce diseases to them.

The results of a painstaking study published after seven years of research showed that the Yanomami have the highest gut bacterial diversity ever reported in a human group – twice as high as the average American city-dweller.

Incredibly, some of their bacterial strains also had antibiotic-resistant genes despite them obviously never having taking antibiotics.

Another amazing piece of research was conducted in 2014, focused on 27 Hadza people from Tanzania in East Africa.
Although the Hadza are modern humans, their lifestyle is believed to closely resemble that of Palaeolithic tribes.
Like the Yanomami, the Hadza are also hunter-gatherers, and once again they showed substantially greater bacterial diversity than the average Houston or St Louis inhabitant, with microbiomes rich in bacteria that help to digest fibers.

Interestingly there was a substantial microbiome difference between the sexes.

When our own data science team compared the microbiota of men and women who have submitted samples to Digbi Health, we found them to be statistically similar.
In the case of the Hadza, however, the difference is thought to be correlated with their sexual division of labor.
Their women forage for tubers and plants, and spend a lot of time with their children, while the men travel widely hunting game and collecting honey.
Apparently both sexes tend to snack during the day, with the result that the women have higher concentrations of bacterial groups such as Treponema, helpful in processing fibers.
Finally, just in case I’ve led you to conclude that all the geographic microbiome studies involve remote tribespeople and hunter-gatherers, consider a fascinating 2010 study which showed that some Japanese individuals are able to extract otherwise inaccessible nutrients from seaweed (the average Japanese person eats 14 grams of it a day) by virtue of ingesting a type of marine bacteria which then transfers its genes to gut bacteria.
In 1940, American health food and weight loss expert Victor Lindler wrote the book “You Are What You Eat”, popularizing the phrase.

76 years later, perhaps it would also be fair to add,
“And You Are Where You Eat”.

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