In Western Tanzania tribes of wandering foragers called Hadza eat a diet of roots, berries, and game. According to a new study, their guts are home to a microbial community unlike anything that's been seen before in a modern human population – providing, perhaps, a snapshot of what the human gut microbiome looked like before our ancestors figured out how to farm about 12,000 years ago.

"There have been relatively few studies of gut microbiota among humans eating pre-industrial diets, relative to humans eating post-industrial ones," said Lawrence David, a microbiologist from Duke University, who was not a part of the study. The new study, published today in Nature Communications, is timely and important, David says, because it provides a snapshot of pre-industrial human's gut microbiota. It also indicates that the ecosystem in our guts adapts not only to our diets but to the environments we live in.

Researchers have known for decades that the biota in our gut vary depending on what we eat. But the Hadza microbiome still turned out to be surprisingly different.

To study the difference between the ancient and modern gut, researchers analyzed stool samples from 16 Italian urbanites and 27 Hadza foragers, of both genders.

The Italians' gut flora was generally what they expected in Western diets, with some Mediterranean influences. The Hadza's poop, however, was like stepping into a lost continent of microbe biodiversity. "The Hadza gut mibrobiome has an entirely unique combination of bacteria from any western population, or rural African population, that's been sampled," said co-author Alyssa Crittenden, a nutritional anthropologist from the University of Nevada, Las Vegas.

Many of the bacteria are species that the researchers had never seen before. And even familiar microbes were present in unusual levels in the Hadza belly. "The Hadza not only lack the 'healthy bacteria,' and they don't suffer from the diseases we suffer from, but they also have high levels of bacteria that are associated with disease," Crittenden said.

Wiggum plots showing the relative abundance and diversity of gut biota from different cultures. The Hadza's doesn't just have unexpected amounts of known bacteria, it has many species that have never been observed before. Image: Amanda Henry

In westerners, Bifidumbacterium is a microbe that many nutrition scientists thought was essential to good gut health, but it is almost completely absent in the foragers. Likewise, high counts of the bacteria Treponema have been linked to maladies like Crohn's disease and irritable bowel syndrome. Neither of these diseases exist among the Hadza, but their guts contain abundant Treponema.

Modern humans have only spent 5 percent of our history as farmers. Before that, most of our species were foragers of some type or other. "Studies like this one are rare opportunities for generating hypotheses about the bacteria that are most sensitive to diet and metabolism in the gut," said David. The Hadza's stomachs represent a reference ecosystem for comparing our modern lifestyles.

That's not to say you should start stocking up on exotic roots, berries, and wild game hoping to create the perfect balance of beneficial bacteria for your belly. Crittenden and her research partners warn against turning their research into a diet, even if the link between the Hadza's gut microbiome and their lower rates of gastrointetinal illness prove true. "Even if you try to emulate the diet of the Hadza, you're not living in the environment," explained Amanda Henry, a dietary ecologist from the Max Planck Institute in Germany, and a co-author of the study. "There are transfers from the soils, from the animals." In other words, it's not just what the Hadza eat that contribute to their remarkable gut flora, it's where and how they are eating it, too.

Among the communities of gut microbiomes that have been sampled – from Americans to Italians to Koreans to vegans – the Hadza's is drastically different. But, what really surprised the researchers was how different the gut communities were between the sexes. The females had much higher levels of several bacteria known to break down fibrous veggies. Both sexes eat copious amounts of tuborous roots, the women do most of the digging, while the men hunt or collect honey. "Even though both groups bring food back to camp, they both snack, so they both eat more of what they collect," Henry said. For the research team, this was just more evidence of how much the gut biota can vary, even between people who spend their entire lives eating different quantities of roughly the same diet.

This research is provocative, but there is a lot more work before the many new questions it raises can bring us answers about the human gut. Henry says she'd like to get samples from more people, and across a broader swath of time. "We really need to look at how gut microbiomes vary by season," she said.