Gaby
Fruits and vegetables are a key part of the human diet, but scientists are only just beginning to understand how our bodies break down cellulose, the most abundant organic compound on Earth. This sturdy substance makes up plant cell walls.
A new international study has uncovered previously unknown microbes in the human gut that can break down cellulose.
What the Researchers Discovered
For decades, scientists believed the human body couldn’t break down cellulose the way cows, horses, sheep, and other herbivores do.
The team set out to find genes from a specific bacterium and to identify related species. They analyzed stool samples from people across different eras and regions. The results suggest we share more with agricultural animals than you might expect.
It turns out our gut contains several types of microbes that consume cellulose, which had previously gone unnoticed. One type is closely related to bacteria found in hoofed mammals, another to bacteria in primates, and a third is human-associated.
All three belong to the genus Ruminococcus. Strains from this genus turn up in both healthy and unhealthy human guts. They also carry genes for cellulose digestion, according to Science Alert.
In stool samples from ancient humans—particularly hunter-gatherers who lived 1,000 to 2,000 years ago—these microbes were abundant. But in modern industrial societies, those microbes are rare. For example, one of the types appears in only about one in 20 people in the U.S., China, Sweden, and Denmark.
Study lead Sara Morais, a microbiologist at Ben-Gurion University in the Negev, says these species have declined in human guts—likely because Western lifestyles have reduced dietary cellulose. Diets in developed countries typically contain less plant fiber, which these microbes need.
If Ruminococcus microbes are deprived of plant fiber, their numbers likely fall. Researchers worry that losing these species could contribute to worsening metabolic health in urban populations.
The authors say there may be potential to enrich these species in the human gut through dietary supplements or specialized probiotics.
What Else the Team Found
Tom Van de Wiele, a co-author from Ghent University in the Netherlands, says industrialization may have caused a huge loss of gut microbial diversity. “We’re losing microbes that helped improve our gut health,” he said.
The researchers say the study is an important step forward. It sheds light on previously unknown bacteria that may have played important roles in human gut health.
Evolutionary analysis indicates the human-associated Ruminococcus strain came from ruminant animals’ guts—likely during domestication.
So maybe, at one time, contact with domesticated animals helped our ancestors digest plants better. Once Ruminococcus established itself in the human gut, it became a resident species.
The results of the study were published in the journal Science.
