Industrialised nations tend to prefer processed food ingredients over a plant-based diet with increased fibre levels
The study also discovered three new species of cellulose-digesting bacteria in the human gut. Photo for representation: iStock A new study has linked growing consumption of processed food with declining levels of gut bacteria that help digest plant cellulose, especially in people in industrialised countries.
The study, published in journal Science, also discovered three new species of cellulose-digesting bacteria in the human gut. These bacteria were prevalent among rural populations as well as the great apes, ancient human societies and hunter-gatherer communities, the paper found.
The decline of these bacteria species potentially impacts energy balance and other health-related aspects, the researchers wrote in the paper. All mammals, including humans, rely on the gut microbiome to digest cellulose, the main component of plant fibre.
These microbes convert these indigestible compounds into short-chain fatty acids, which, in turn, supply energy to the host.
For long, it was believed that humans did not host cellulose-degrading gut microbes. It was only in 2003 that scientists discovered that human gut bacteria were indeed degrading this complex sugar molecule. The species was identified as Ruminococcus champanellensis.
“Despite this discovery, cellulose degradation and fermentation in the human gut are rare or absent in most humans,” the researchers wrote.
So they designed the study to address questions on how prevalent cellulose-degrading bacterial species are in the mammalian gut, how they adapt to host lifestyle and diet and whether there are more such undiscovered bacterial residents in the human gut.
The team analysed samples from 75 animal species, including wild and domesticated animals such as non-human primates (macaques, baboons, gorillas and chimpanzees) and ruminants, as well as various human cohorts.
They used the known human strain Ruminococcus champanellensis and the related species Ruminococcus flavefaciens found in rumens (the first chamber of a ruminant animal’s stomach) as a reference to identify related species by searching for key genes.
They found them in 25 genomes of rumen and 22 of human origin. In humans, three new cellulose-degrading bacteria named, Candidatus Ruminococcus primaciens, Ruminococcus hominiciens and Ruminococcus ruminiciens were identified.
The human microbes digested monocots such as maize, rice and wheat, which are major components of the human diet. Similarly, non-human primate strains could degrade chitin, a polymer abundant in insects.
More specifically, the human microbe Ruminococcus hominiciens was found to primarily reside in the guts of humans and great apes.
Ruminococcus hominiciens, according to the researchers, likely originated in the ruminant gut and then colonised humans possibly during domestication.
Further, the researchers saw variations in the prevalence of human cellulose-degrading bacteria in different countries.
In industrialised countries, including Denmark, China, Sweden and the United States, the collective prevalence was found to be 4.6 per cent, while it was 43 per cent among humans that lived from 1,000 to 2,000 years ago, 21 per cent in hunter-gatherers and 20 per cent in geographically diverse rural societies.
This suggests that these microbes currently exist in limited proportions in human populations and were previously more widespread and abundant. “Differences in their prevalence among human populations may reflect dietary variation between industrialised and non-industrialised societies,” the paper said.
The differences were down to the intake of dietary fibre, as Hadza hunter-gatherers in east Africa are known for their high-fibre diets, amounting to 80 to 150 grammes per day. Rural populations’ intake was estimated to be around 13 to 14 g per day while industrialised populations consume 8.4 g per day.
Industrialised nations, according to the paper, tend to prefer processed food ingredients over a plant-based diet with increased fibre levels.
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