Study Shows City Dwellers Are Losing Ability To Digest Plants

A new research conducted by a team of scientists who’re a part of The American Association for the Advancement of Science, has linked growing consumption of processed food with declining levels of gut bacteria, which help humans digest plant cellulose. This is particularly true of people in industrialised countries. 

The study published in the Science journal found that the the lack of fibre in western, meat-heavy diets might be affecting the way guts of urban dwellers digest tough plant matter. Like any other mammal, human stomachs host diverse colonies of microbes that help break down food components into digestible components. Interestingly, three new species of cellulose-digesting bacteria in the human gut were discovered in 2003. 

Now, these bacteria have been used as a genetic reference by researchers as they have examined through human faecal samples to analyse the gut microbiome of humans from a number of regions and different times, dating back a thousand years. Quite a few cellulose-loving microbes were found in mammals and other primates, but were extremely rare among modern humans from industrialised societies. 

"These findings collectively imply a decline of these species in the human gut, likely influenced by the shift toward westernised lifestyles," the study’s authors explained. As per the study, the researchers believe that ‘Ruminococcus’ microbes have lost ready access to fibre-rich diets, causing their numbers to dwindle in the guts of urban dwellers, which is hampering their ability to process plant matter, and also make their metabolic health worse.

There was a clear variation in the prevalence of human cellulose-degrading bacteria in industrialized and nonindustrialized societies. In industrialised countries, including Denmark, Sweden and the United States, the collective prevalence was 4.6 per cent, while it was 43 per cent in the human pooulation that lived from 1,000 to 2,000 years ago.

“Differences in their prevalence among human populations may reflect dietary variation between industrialised and non-industrialised societies,” the paper said. The study references Hadza hunter-gatherers in east Africa are known for their high-fibre diets, amounting to 80 to 150 grammes per day. While modern rural populations’ intake has been estimated to be around 13 to 14 g per day, industrialised populations consume 8.4 g per day and also tend to prefer processed food ingredients over a fibrous plant-based diet.