Does a rich intestinal microbiota protect against colorectal cancer, and does ultra-processed diets, by altering the microbiota, promote the onset of this disease, which is on the rise among young people? These questions are at the heart of new research conducted at the Pasteur Institute.
Colorectal cancer is one of six cancers (including brain, kidney, breast, etc.) whose incidence increased among 15-39 year-olds in France from 2000 to 2020, according to Public Health France, causing concern.
While it is well known that a healthy lifestyle reduces risks – avoiding tobacco and alcohol, eating a varied and balanced diet, and exercising regularly, etc. – the still little-known link between colorectal cancer and the intestinal microbiota is the subject of much research.
A complex ecosystem of microorganisms that live in our intestine, the intestinal microbiota is essential to our good health: digestion, immunity, protection of the intestinal mucosa, etc.
We know that our diet influences its composition and functioning: an unbalanced microbiota can promote inflammation and the production of toxic substances, deregulate our immune system and thus increase the risk of developing cancers, including colorectal cancer.
At the Pasteur Institute in Paris, researcher Benoit Chassaing, Inserm research director, heads the "Microbiota-Host Interactions" laboratory - created a year ago - where he explores the influence of modern diet on the intestinal microbiota and its link with colorectal cancer in particular.
"We study emulsifying agents extensively, the most commonly used additives to extend shelf life and improve the texture of products: ice cream, sandwich bread, chocolate bars, salad dressings, etc. We have been able to show that they alter the microbiota," explains the scientist.
– “Passed on to the next generation” –
At the end of July, the journal Nature Communications published an Inserm/Institut Pasteur study by his team, showing that in mice, the consumption of food additives by the mother alters the microbiota of the offspring, increasing the risk of developing chronic inflammatory diseases.
Female mice were exposed to common emulsifiers (E466, E433) 10 weeks before gestation, and then during pregnancy and lactation. The researchers noted an alteration in the microbiota of the pups: an increase in flagellated bacteria, which can trigger an inflammatory response.
"Our work shows that in mice, this unhealthy microbiota is passed on to the next generation: these children recover bad bacteria that make them very susceptible in adulthood to developing chronic inflammatory bowel diseases, metabolic dysregulation and obesity," says the researcher.
However, some of these emulsifiers "are also found in powdered milk and foods for young children," he notes.
Clinical trials on humans remain to be conducted, with the aim of one day adopting regulations promoting the use, by the food industry, "of harmless additives and the cessation of the use of harmful additives," continues Mr. Chassaing.
His team is also studying the layer of mucus that lines the intestinal wall: normally sterile, when the microbiota is disrupted, it can be colonized by bacteria that promote the appearance of precancerous lesions, then colorectal cancer.
In the lab, one room houses the "in vitro" microbiota, with which the team conducts further research. Heated to 37 degrees Celsius, devoid of oxygen, it reproduces the conditions of the intestine: behind a plastic wall, 48 small compartments contain bacteria that feed on the alimentary bolus (masticated food mass, editor's note), as during digestion.
We can observe the reaction of 48 unique microbiotas to food additives: we see if one is more sensitive than the other to the impact of these components of ultra-processed food - today tested before marketing for their toxicity and their impact on DNA, but not on the microbiota.
On October 8, the Pasteur Institute will open its Paris campus to the general public, launching the 19th edition of Pasteurdon, its annual fundraising campaign.
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