The gut bacteria of four Himalayan populations differ based on their dietary lifestyles, according to a study.
All four populations -- the Tharu, the Raute, the Raji and the Chepang -- are longtime residents of the Himalayan foothills, with similar languages, cultural practices and ancestry, said researchers at the Stanford University in the US.
The Tharu have practiced agriculture for the past 250 to 300 years, the Raute and the Raji have practiced agriculture for the past 30 to 40 years; and the Chepang are hunter-gatherers.
The study, published in the journal PLOS Biology, found that the composition of the gut microorganisms, or gut microbiome, of each population differed based on whether and how long ago it had departed from a hunter-gatherer lifestyle.
"This study indicates that human microbiomes may have changed gradually as human lifestyle changed, and those changes can happen within a human's lifetime," said Aashish Jha, a postdoctoral scholar at Stanford.
The study is the first to show a change in gut microbiome compositions between closely related populations living within the same geographic area.
Within each of our intestines lives a community of trillions of bacteria that make up our gut microbiome.
These bacterial communities are essential for digesting foods and regulating our immune system.
Beginning some 1.8 million years ago, humans were a nomadic, hunter-gatherer species whose diet consisted of fish and meat, along with seasonal seeds, nuts, roots, vegetables and berries.
It wasn't until around 10,000 years ago that we transitioned to farming, radically altering our diets, cooking techniques and way of life.
To examine whether this change in lifestyle affected gut microbiome compositions, the researchers collected stool samples from 56 individuals across the four Himalayan populations and from 10 individuals in a control group of North Americans of European descent.
The researchers also gathered information on individuals' demographics, dietary practices, health status, medications, use of tobacco and alcohol, and several other environmental variables.
They determined the degree to which the lifestyle variances across the four Himalayan populations correlated to differences in their gut microbiomes.
An analysis of the samples' contents revealed four distinct types of gut microbiome.
Even more exciting, these distinctions paralleled the populations' transition from hunter-gatherers to farmers.
The researchers found that subdivisions of bacteria, including Ruminobacter and Treponema, which are abundant in foraging groups like the Chepang, decrease as populations depart from the hunter-gatherer lifestyle.
In fully industrialised populations, such as those in North America, these bacteria are rare or completely absent.
Strains of other bacterial phyla such as Actinobacteria and Verrucomicrobia are rare or nonexistent in hunter-gatherers but appear as farming and industrialisation take hold.
These results also suggest that pronounced changes in human gut microbiomes can occur within decades of a population's departure from a hunter-gatherer lifestyle.
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