By studying the microbiome of existing hunter-gatherer tribes, researchers draw a link between poor quality diets and a host of health issues.

It’s long been thought that what’s happening inside our gut could determine our overall health.

Now, researchers from Stanford University may have found out why, and it’s because of our gut microbiome, or lack thereof.

Your microbiome is made up of the thousands of microorganisms that take up residence in the digestive system. These microscopic organisms are present from the moment you’re born and are then shaped by dietary and other factors for the remainder of your life.

“Stretched out, the human intestines have the surface area of a small garden. Imagine now trillions of microbes on the surface, interfacing with the human body… there are huge implications for energy harvesting, education of the immune system, and chronic inflammatory diseases, among many others,” Sam Smits, PhD, a researcher at Stanford University, told Healthline.

The human diet has radically changed over the past 15,000 years thanks to the advent of agriculture. In just the past century, the introduction of antibiotics, cesarean births, an increase in sedentary activity, and the slow replacement of fiber-rich foods, fruits, and vegetables with processed, fiber-free options, has also led to significant changes in the human body.

Stanford researchers wanted to see how diet impacts our microbiome. To do that they examined a group of hunter-gatherers in Tanzania known as the Hadza.

“Surviving hunter-gatherer populations are the closest available proxy to a time machine we in the modern industrialized world can climb into to learn about the ways of our human remote ancestors,” Justin Sonnenburg, PhD, associate professor of microbiology and immunology, and lead author of the study, said in a press release.

Members of the Hadza group who stick to the traditional hunter-gatherer lifestyle have a diet that consists mainly of meat, berries, tubers, and honey. The Hadza diet is at the mercy of the seasons — in the dry season meat is eaten more, while in the wet season berries play a larger role.

The researchers collected 350 stool samples from members of the Hadza over one year. They found that their gut microbiome is different from and more diverse than that of people living in the industrialized world. They also found that specific types of bacteria present for the Hadza in the dry season is almost entirely extinct in the vast majority of people living in the industrialized world.

So does it matter that those living in the Western world are missing some of these microbial species? According to Dr. Eugene B. Chang, AGAF, scientific advisory board member for the American Gastroenterological Association Center for Gut Microbiome Research and Education, it could be.

“[People] consuming Western-type diets may be losing key microbial species that are important for maintenance of health. Now with consumption of high-fat, high-refined sugar diets, and low-fiber Western diets, those critical microbial groups are lost… this results in mismatches and absence of key microbes that are essential for health,” he said.

The Stanford research is one of a number of studies in recent years that suggest diet and gut health play an important role in overall well-being.

“There was accumulating evidence in disparate studies that the microbiotas possessed by traditional and industrialized population are different in terms of composition. There is also evidence that there is a significant rise in chronic diseases within Western populations. We also know that the microbiota may play a key role in many of these diseases. Together then, this evidence suggests that the microbiotas that industrialized populations possess do not provide protective properties against these diseases that are on the rise,” Smits told Healthline.

If the gut microbiome become abnormal, or form improperly, it can have significant consequences for overall health.

“It can have negative effects that can potentially contribute to, or trigger, developmental problems in immunity and metabolism, complex immune disorders (inflammatory bowel diseases, type 1 diabetes), liver diseases, obesity, under-nutrition, diabetes, and cardiovascular disorders,” Chang said.

A 2016 study, also led by Sonnenburg, showed that depriving mice of dietary fiber greatly reduced the diversity of gut-microbial species. This was then restored when dietary fiber was reintroduced. However, if the fiber deprivation was maintained for four generations, the gut-microbial species that once bounced back were lost permanently.

A similar phenomenon could be occurring inside the guts of those in the Western world, and the evolution of our diet has played a significant role.

“Hunter-gatherers had to live on what was available. The diets were limited to what was seasonally available and hence the seasonal variation in their gut microbiomes. In Western societies, we can change our environment and are no longer dependent on finding food. We can go to the grocery store, choose from many varieties of products, and know that they are available any time of the year. Our choices are often guided by what is inexpensive, convenient, and satisfying which translates into ready-packaged, processed, high-fat, high-caloric, low-fiber, and inexpensive foods,” Chang said.

In many ways, it could be argued that the Hadza diet is much healthier than the typical diets of those in the Western world: no processed food, no refined sugars, and a large intake of dietary fiber.

“The Hadza get 100 or more grams of fiber a day in their food on average. We average 15 grams per day,” Sonnenburg said.

But attempting to restore the missing gut microbiome that may be leaving us exposed to certain diseases may not be as easy as replicating the Hadza diet.

“Changing people’s diets and lifestyles in Western societies is not practical, because they won’t do it,” Chang told Healthline.

“However, we might be able to replenish missing components of their gut microbiome and keep them around by supplementing their diets with certain types, and sufficient amounts of, dietary fiber supplements, using microbiome analysis to determine how this regimen can be tweaked.”