Whether it's giving us affluenza, causing first world problems, or (if you're fact-free inclined) "injuring" us through vaccines, a lot of people think the modern world is making us sick. And yet, a whole raft of conditions we may think of as being "modern" afflictions – from depression and anxiety to obesity, and even autism and ADHD – have actually been linked in recent years to a much more personal ecosystem: the one inside our guts.

So when a group of five people – as well as two of their children – escaped la carrera de ratas of Venezuela's largest city Caracas to spend 16 days living in a jungle village with the indigenous Ye'kwana tribe, scientists from US and Venezuelan institutions saw an opportunity to see how a more traditional way of life would affect their gut microbiomes.

Published in the open-access journal mSphere on an admittedly tiny sample population, their study compared the city-dwellers' gut and skin bacteria to those of the villagers – aiming to test whether the Caraquenians' microbiota would become more diverse as a result of their back-to-basics lifestyle.

"In this village, there was no market economy, no bodega, no Coca-Cola – so this represented a radical shift in diet from a high percentage of processed foods in urban places to zero processed foods and an all-natural diet," lead author Maria Gloria Dominguez-Bello explained in a statement. 

It was a big culture shock. Living with the Ye'kwana meant a radical change in the visitors' routine: they ate two meals a day – soup, with a bit of meat or fish – and snacked on the starchy cassava root to keep them going in between. They swapped their alarm clocks for the villager's natural circadian rhythms. They washed in the river with no soap or toothpaste. And throughout their stay, researchers took microbe samples from their nose, mouth, skin, and feces.

Now, we already knew that city-dwellers have much less diverse gut microbiomes than hunter-gatherers – and that's a bad thing. But previous studies have hinted that our gut ecosystems might be sensitive to diet and lifestyle changes, so the researchers wanted to see if immersion in a traditional lifestyle – free from artificial sweeteners, processed food, and abundant antibiotics – might shift the urban gut microbiomes to be more diverse.

Unfortunately, it seems the answer may be no – or, more intriguingly, not for everyone. 

"Surprisingly, none of the adult visitors' microbiota shifted significantly during the visit," notes the statement. But "the two children's gut microbiota trended toward a higher number of total microbial species present," it adds. 

"Although these results were not statistically significant and in just two subjects, the researchers saw this as interesting nonetheless, given the children's ages of 4 and 7."

Up until now, scientists had thought that our gut microbiomes were more or less fixed by the age of three – but the team's findings put that into question.

"This indicates that the window for maturing your microbiome may not be 3 years of age, but longer," Dominguez-Bello explained. 

This is big news. Having diverse gut microbiota is important to protect against disease and extract nutrients from our food, but it's something urban residents appear to struggle to achieve. This study now suggests that, after childhood, we're essentially stuck with the gut we've got – making it even more vital to get a varied diet while you're still young.

"[T]hese results raise an interesting possibility that urban children who eat a more traditional, high-fiber, low-fat and low-processed diet early in life might cultivate a more diverse set of gut microbes," explains the statement. "Conversely, adults may have a limited response due to their low microbiome plasticity."

To explore these findings in more detail, the team plans to do a larger study in the future, taking 12 children for an immersive "summer camp" in the jungle. But unfortunately for the grown-ups, it turns out gut bacteria may exist on a "use them or lose them" basis - adults can kill off all the glucose-digesting microbiota we want, but there's no diet that can bring it back once it's gone.

[H/T: Inverse]