An average adult carries up to half a kilogram of bacteria in their body, most of it in the intestines. These microbes develop shortly after birth and help digest food, breaking down fibre that the body cannot process on its own.
Scientists now say this vast community of bacteria, known as the microbiome, plays a role that goes well beyond digestion.
“We really rediscovered the gut microbiome over the last 10 to 20 years as a forgotten, or critical organ – a part of our body that really counts for our health,” explains Patrick Veiga, research director at MetaGenoPolis, a microbiome research lab near Paris.
A visit to the microbiome lab and more on the French gut microbiome in the Spotlight on France podcast:
Because a large number of immune cells are in the intestines, they interact closely with bacteria. People with immune disorders appear to have different gut microbes.
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Scientists are working to understand why that is the case, especially because industrialised countries, including France, have seen an increase in chronic, immune-related diseases like Crohn’s, ulcerative colitis, and diabetes.
“We’re seeing an increase of these non-communicable diseases,” Veiga tells RFI, pointing also to neurological conditions such as Alzheimer’s or Parkinson’s.
“Sometimes these can be explained by age – we are ageing. But some of these are not explained by these factors, and we believe that the gut microbiota can be a missing piece of the puzzle.”
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Le French Gut
In 2023 Veiga’s lab became the operational hub for Le French Gut, a national study aiming to collect faecal samples from 100,000 people across France to identify gut bacteria and track long-term health outcomes.
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The project is France’s contribution to the global Million Microbiome from Humans Project, which is looking to gather 1 million samples worldwide.
Le French Gut has already collected 30,000 samples, which arrive at Veiga’s lab in batches of 1,000 from hospitals running the clinical trial.
Machines extract DNA from about 2,000 samples each month, and the DNA is then run through genetic sequencers to identify the hundreds of different species of bacteria that can be present in the human gut.
Participants also fill out questionnaires about their health and what they eat. Because researchers can access data from France’s public health system, they can follow participants for decades to see whether certain diseases develop and whether earlier changes in the microbiome could have predicted them.
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“The ones who will develop diseases or eventually those who will die, maybe the data will allow us to find a pattern that could explain the disease that happened five or 10 years after they enrolled in the study,” Veiga says.
Diet and diversity
A healthy microbiome is one with many different kinds of bacteria, and it is strongly impacted by diet. As a result, gut microbiomes vary across countries and cultures.
France offers a particularly interesting case because of its geographical and cultural diversity.
“France has this large territory with different cultures and diets,” Veiga explains. “There are also different climates. So it’s interesting to look at different regions in France to look at the impact of different local diets on the gut microbiome.”
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The French diet includes fermented foods such as yogurt and cheese, as well as wine.
“This can make a difference on the gut microbiome,” says Veiga. “So I think we will see signatures in this project that we will not see elsewhere.”
Other factors that influence the microbiome include antibiotic use, physical activity and stress, which vary between individuals and regions.
Recruiting kids
Study participants have so far skewed female – 70 percent are women between the ages of 40 to 60 years old.
“Maybe they’re more generous than the men?” mused Veiga, who said there is an under-representation of older people and those under 30, which is why the study has started reaching out to kids.
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Through public service announcements, social media posts and games, researchers hope to recruit children who might overcome their squeamishness about the subject matter and be drawn in by the science behind the project.
“Teenagers have a different motivation and maybe lack of motivation in some cases. And to recruit them will be really another challenge than recruiting infants or younger children,” Veiga says.
Initial results
While the full results will take years to come out, Veiga says there are early findings, including a confirmation of previous research showing differences in the microbiomes of healthy people versus those with diseases, with specific bacteria profiles linked to specific diseases.
Some conditions, such as cancer, can alter the gut microbiome before symptoms appear, which could provide early warning signs and improve treatment.
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“The idea would be to use this information to better diagnose or understand the disease,” Veiga says.
“Maybe we can try to find novel cures targeting the gut microbiome, to treat and to prevent disease.”
More on the French microbiome, and a visit to Le French Gut’s lab in the Spotlight on France podcast, episode 137. Listen here.