City Dwellers Have Slowly Been Losing Ability For Plant Matter Digestion Due to Decline of Cellulose-Eating Microbes, Study Finds

According to a new study, cellulose-digesting microbes were found to be clearly rare among modern and urbanized city dwellers.

Plant Matter Digestion

Though fruits and vegetables are key to the human diet, scientists have just started learning more about how the human body breaks down Earth's most abundant organic compound: cellulose, which lines plant cell walls.

A new study entitled "Cryptic diversity of cellulose-degrading gut bacteria in industrialized humans" has discovered some microbes, which were previously unknown, within the human gut. These novel microbes can break down cellulose.

It was assumed for decades that the human body cannot break down cellulose the same way the guts of other animals can. It was only in 2003 that scientists found out that the gut bacteria of humans are capable of digesting such fibers.

Now, as for the new study, it mainly depended on the genes of the same bacterium in order to find other similar microbes. The analysis made use of fecal samples to examine the human gut microbiome from different regions and times. Findings suggest that humans share more similarities with farm animals than previously thought.

It turns out that the human gut has various cellulose-digesting microbial species that have remained unnoticed until now. There is one specific species that is strongly related to ungulate materials that chew cud, another with humans, and another with primates.

These three are part of the Ruminococcus genus, which is already known to have both unhealthy and healthy representations in the guts of humans. The genus also has genes involved in cellulose digestion.

These three microbial types were found to be abundant in fecal samples from rural populations, hunter-gatherers, and prehistoric humans from 1,000 to 2,000 years ago.

Microbial Decline Observed in City Dwellers

However, among populations in industrialized and modern societies, these gut microbes were found to be notably rare. The study authors note that such findings imply that the species has seen a decline in the human gut. Such a plummet may have been influenced by the preference for more western lifestyles.

The researchers note that it is possible that if these bacteria are deprived of the fibers of plants, their numbers within the gut end up reducing. What could be worrisome is how the missing species could be influencing poor metabolic health among urbanized and modern individuals.

Such a possibility still requires further investigation. However, the study authors think that intentional enrichment or reintroduction of the species in the human gut could be possible.

Overall, this new study is a crucial step forward, as it sheds light on gut bacteria that were previously unknown and that could be crucial players in human gut health. Evolutionary analysis also argues that the Ruminococcus bacterial strain may have been transferred to humans from ruminant guts, possibly through domestication.

Compared to the species of Ruminococcus bacteria in other animal and primate guts, the ones in humans have seemingly adapted to their different ecosystems and acquired genes from the gut microbiomes that neighbor them.

However, after thousands of years, such a colonization feat could be threatened. In some regions of the world, the guts of humans may no longer be able to offer a suitable home for such microbes.