Gut Bacteria boost our immunity, protect us from infection and produce the enzymes we need to digest our food. Without these bacteria, we wouldn’t survive.
Humans in the U.S. have lost a third of their microbial diversity, mostly on their skin and in their stomachs and digestive tracts, said Maria Gloria Dominguez-Bello, associate professor of medicine at NYU. Microbe extinction may be at the root of modern plagues like asthma, allergies, diabetes, obesity and even some forms of cancer.
“The human body isn’t just what you see in the mirror,” she said. “It’s an ecosystem, just like a forest, just like the ocean, where microbes of many different species are interacting to support the whole.” “It’s shocking when you look at numbers how much total diversity has been lost.
“Not caring about your microbiome is like not caring about your liver or your spleen,” Zimmer said. “They’re an important part of your body. You need to be concerned.”
Low-Fiber Diets Cause Waves of Extinction in the GutOver generations, mice deprived of fiber permanently lost some species of gut microbes. What does this mean for human health?
Fiber is a broad term that includes many kinds of plant carbohydrates that we cannot digest. Our microbes can, though, and they break fiber into chemicals that nourish our cells and reduce inflammation. But no single microbe can tackle every kind of fiber. They specialize, just as every antelope in the African savannah munches on its own favored type of grass or shoot. This means that a fiber-rich diet can nourish a wide variety of gut microbes and, conversely, that a low-fiber diet can only sustain a narrower community.
Sonnenburg, his wife Erica, and the graduate student Samuel Smits confirmed this idea in a recent experiment. ... Sonnenburg and Smits bred the mice from their first experiment, they saw that low-fiber parents gave birth to pups with narrower microbiomes, which lacked species present in the progeny of high-fiber parents. And if these bacteria-impoverished pups also ate low-fiber food, they lost even more microbes, especially those from the fiber-busting Bacteroidales group. As four generations ticked by, the rodents’ guts became progressively less diverse, as more and more species blinked out.
It also became increasingly hard to reverse these changes. If the fourth-generation mice switched to high-fiber meals, some of the missing microbes rebounded, but most did not. In other words, these species weren't just lying in wait in small numbers, waiting for the chance to bloom again; they had genuinely vanished.
These changes parallel those that have taken place over the course of human history. Many studies have now shown that the gut microbiomes of Western city-dwellers are less diverse than those of rural villagers and hunter-gatherers, who eat more plants and thus more fiber. The Stanford researchers’ experiment hints (but doesn't confirm) that this low diversity could be a lasting legacy of industrialization, in which successive generations of low-fiber meals have led to the loss of old bacterial companions. “The data we present also hint that further deterioration of the Western microbiota is possible,” the team writes.
There’s evidence that a diverse microbiome can better resist invasive species like Salmonella or Clostridium difficile, while low diversity is a common feature of obesity, inflammatory bowel disease, and other conditions.
“It is possible that rewilding the modern microbiota with extinct species may be necessary to restore evolutionarily important functionality to our gut.”
Sonnenburg's concern is that these changes play out over millennia, and hosts and microbes have time to acclimate to their new relationships. By contrast, our modern diets and lifestyles are changing our microbiomes very quickly, leaving us with communities that we haven't adjusted to. “Our human genome is constantly trying to keep up with this moving target of a microbial community,” he says. “If there are times when changes are exceptionally rapid, it might be problematic for host health.”