On the cellular level, you’re just as much bacteria as you are human.
Previously, scientists believed the human body harbored on the order of 10 times more bacteria cells than human cells. But recent reports have claimed that number was a myth, and the ratio is more 1:1.
Regardless, these bacteria cells play an important role, especially when it comes to the gut. In 2008, scientists discovered the human colon was populated by at least 5,600 different bacteria species. And what do these microscopic organisms feed on? Fiber.
In industrialized societies, diets come and go like many cultural trends. But one diet that’s got Stanford Univ. School of Medicine investigators concerned is the low-fiber diet.
Already, humans from industrialized societies consume around one-tenth the fiber that humans from hunter-gatherer or rural agrarian populations consume. And scientists have found that hunter-gatherer microbiomes are usually more diverse.
“The reduced diversity of the gut microbiota in Western populations compared to that in populations living traditional lifestyles presents the question of which factors have driven microbiota change during modernization,” the researchers write in Nature.
The new Stanford Univ. study—performed on mice, which had their guts populated by microbes from a human donor—showed that low-fiber diets diminish the species present in microbial ecosystems. Additionally, the results indicate that loss of species diversity is irreversible three or four generations later.
After introducing human microbes to the initially aseptic mice, the researchers split them into two groups. While fed the same amount of protein, fat, and calories, one mice group was fed a diet high in plant-derived fiber, while the other group’s diet was nearly devoid of fiber.
Stool samples were collected and analyzed. Within a couple of weeks, researchers noticed that over half the bacteria species—in the mice fed the low-fiber diet—had shrunk by over 75%. Some species were completely absent.
Seven weeks into the experiment, the low-fiber diet mice were switched to a high-fiber diet for four weeks. The gut-bacteria only partially recovered, with about one-third of the original species never fully recovering.
Bred and kept on the low-fiber diet, the mice passed on their depleted gut-bacterial ecosystems to their offspring. The researchers reported that by the fourth generation, the low-fiber diet mice had about three-fourths less bacteria species in their gut than their great-grandparents.
Full restoration of lost species was only achieved by a fecal transplant, which was achieved by taking fecal contents from fourth-generation high-fiber diet mice.
The find has led the researchers to ponder if successive generations of industrialized humans will continue losing bacterial species in the gut.
Keep in mind, fiber plays only a small role in this. The proliferation of antibiotics and less-frequent breastfeeding have also played a role in diminishing bacteria populations.
What’s the remedy? Well, study author Justin Sonnenburg, an associate professor of microbiology and immunology, suggested not washing hands after gardening and less overindulgence in antibiotics is a step in the right direction.