Study leader Prof. Jeroen Raes, of the University of Leuven (KU Leuven) in Belgium, and his team say their findings may better inform future studies investigating how the gut microbiome – the population of microbes that live in the intestine – affects human disease.
The results – recently published in the journal Science – come from the Flemish Gut Flora Project, which the team says is one of the largest population-wide studies to assess the variation of gut microbiota among healthy individuals.
The gut microbiome consists of tens of trillions of microorganisms, including at least 1,000 bacterial species, and can weigh up to 2 kg.
While around one third of gut microbiota is common to the majority of people, around two thirds are specific to each individual. As such, researchers are interested in how the gut microbiome may impact human health.
For their study, Prof. Raes and colleagues analyzed the stool samples of more than 1,000 healthy individuals from Belgium who were part of the Flemish Gut Flora Project.
Through their analysis, the team identified 69 factors that are linked to the diversity or composition of gut microbiota, many of which are associated with transit time – how long it takes for food to move from the mouth to the end of the intestine – diet, medication use, gender, age, and overall health.
The researchers then combined their results with those of other analyses across the globe, from which they identified 14 bacterial species that make up the microbiota present in the intestine of each and every person.
Prof. Raes notes that most studies have focused on how the diversity of gut microbiota influences the development of specific diseases.
“However, analyzing the ‘average’ gut flora is essential for developing gut bacteria-based diagnostics and drugs,” he says. “You need to understand what’s normal before you can understand and treat disease.”
Transit time was found to be the heaviest influence on gut microbiota composition, according to the researchers, and diet – particularly fiber intake – was also found to play a key role.
Interestingly, the team found that intake of dark chocolate was found to drive the presence of a specific bacterial population, and beer intake was also a key influence on the composition of gut microbiota.
Supporting previous studies, the researchers also found a link between medication use and gut microbiota composition; use of laxatives, antibiotics, hay fever medication, and hormones used for birth control or menopause symptoms were found to affect gut microbiota diversity.
Contrary to previous research, the team also found that delivery method at birth or whether an individual was breast-fed as a baby did not influence gut microbiota composition in adulthood.
On assessing data from the Dutch LifeLines Study, the researchers found they were able to replicate their findings; around 90 percent of the factors they identified that influence gut microbiota were present in the Dutch cohort.
“Such replication adds a tremendous amount of robustness to the results,” notes Prof. Raes.
Additionally, from their analysis of the Dutch cohort, the researchers found buttermilk was a key influencer for gut microbiota composition.
The findings from this ongoing project have important implications for future research into human disease, according to the team.
“These results are essential for disease studies. Parkinson’s disease, for example, is typically associated with a longer intestinal transit time, which in turn impacts microbiota composition.
So to study the microbiota in Parkinson’s disease, you need to take that into account. These and many other observations can help scientists in their research into future therapies.”
Prof. Jeroen Raes
While the researchers say their findings have shed important light on what factors might influence gut microbiota composition, they note that there is much more to learn; their results only explain around 7 percent of gut microbiota variation.
The researchers estimate that around 40,000 human stool samples will need to be collected before an entire picture of gut microbiota composition can be identified, and this is something they hope to achieve with the Flemish Gut Flora Project.
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