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In this photo taken Sept. 7, 2012, a Yanomami Indian woman cooks plantains at a village called Irotatheri in Venezuela’s Amazon region.

Ariana Cubillos/Associated Press

Most modern Westerners enjoy a lifestyle that confers tremendous health advantages, including ready access to clean water and medicine. But now it appears that we have lost something along the road to modernization – a lot of somethings.

In a study published on Friday in the journal Science Advances, an international team of researchers has shown that the bacteria living in the digestive tracts of previously uncontacted hunter-gatherers discovered in Venezuela are the most diverse ever found in any human group.

The result supports what many scientists have long suspected: that modern living has cleaved away large segments of the bacterial population, called the human microbiome, that once lived with and within our ancestors. A better understanding of that deficit could explain and potentially help prevent a host of chronic diseases that are common in Western society, including obesity, asthma, allergies and diabetes.

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Such disorders "may be related to a degraded microbiome," said Maria Dominguez-Bello, a researcher at the New York University School of Medicine, who led the study.

The finding is further bolstered by a separate study released this week that compared the gut bacteria of North Americans with two groups of rural Papua New Guineans.

"Our motivation is to try to find out what is the real human microbiome – the one with which we evolved," said Jens Walter, a microbial ecologist at the University of Alberta and lead author on the Papua New Guinea study, published in Cell Reports. Dr. Walter also participated in the Venezuelan project.

In lieu of a time machine, he said, "what we have left is to look into human individuals that don't live a Westernized lifestyle."

And that look carries some important implications, researchers behind the two reports said.

In the Venezuelan study, which involved a genetic sampling of the bacteria found in the feces, saliva and skin of 34 Yanomami villagers, researchers found genes that are associated with antibiotic resistance. Since the group had little or no contact with Western medicine before their discovery in 2008, researchers hypothesize that the traces of antibiotic resistance in their bacteria were acquired naturally, through an exchange of microbial genes with soil bacteria.

Experts say the results speaks to the versatility of bacteria and the apparent ease with which they develop resistance to the drugs we create to fight infection. It emphasizes that antibiotics should be deployed with care since the capacity for drug resistance is naturally occurring in human-dwelling bacteria.

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The Yanomami group was first spotted from the air and later contacted by officials, The motivation for making contact is to provide vaccinations that will protect the Yanomami against diseases that they may become exposed to through illegal mining activities in the Amazon, Dr. Dominguez-Bello said. Health workers collected the samples used in the study in 2009.

Over all, the Yanomami were found to have 30 to 40 per cent greater microbial diversity than native Venezuelan groups that have more contact with Westerners and about double the diversity of North Americans.

"I think this just re-emphasizes that in our quest to clean up our world to get rid of infectious bacteria, there are unintended consequences," said Brett Finlay, a professor of microbiology at the University of British Columbia who was not involved in either study.

He added that work supports what is known as the hygiene hypothesis, which suggests that because we now experience more limited exposure to bacteria, "we lack the right bugs to develop our immune systems early in life."

The precise cause of our deteriorated Western microbiome is still a matter of debate.

"It is likely that some combination of our low-quality diet, antibiotic use and other aspects of our lifestyle and medical practice have led to a loss of microbial species as we have modernized," said Justin Sonnenburg, an associate professor of microbiology and immunology at Stanford University.

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In the second study, Dr. Walter said he was surprised not just at the greater diversity in the microbiomes of Papua New Guineans as compared with those of Americans, but also how much uniformity there was between Papua New Guineans, even those from two widely separated villages.

He said this suggested that microbes move between individuals more readily in traditional societies, and that a largely germ-free water supply and sanitation practices in the West limit bacterial mobility.

Dr. Walter stressed the results should not be taken as a reason to abandon the basic public-health advances that have dramatically reduced the incidence of infectious disease in the modern world. Rather, he said, they reveal that those advances have come hand in hand with hidden trade-offs. Understanding those trade-offs in detail could lead to insight in the prevention and treatment of diseases that have become more prevalent in industrialized societies.

"The idea is to move [forward] the exciting basic discoveries on the gut microbiome and health … into something like therapies."

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