No oxygen, a constant temperature of 37 degrees, a continuous flow of culture medium to feed billions of bacteria. To understand why certain food additives seem particularly harmful to our health, a team of scientists from the Cochin Institute in Paris have created “artificial microbiota”. In fact, human stools suspended and moving like in our intestines. But here, they are encapsulated in large plastic tubes made by 3D printers.
In recent years, around the world, epidemiologists have uncovered a correlation between the consumption of ultra-processed foods rich in food additives and the increased risk of contracting certain diseases – obesity, diabetes, cardiovascular pathologies, depression… But at this stage these are only associations, not cause and effect links. To go further, we must therefore try to understand the mechanisms potentially involved.
This is the ambition of researcher Benoît Chassaing, whose pioneering work targets a potential culprit, emulsifiers, and its accomplice, our intestinal microbiota. Emulsifiers represent a large family of additives widely used in industrial kitchens to bind oil and water. They improve the preservation of products and above all, give them texture. They are found almost everywhere: to give volume to sandwich breads and strength to dessert creams, margarines and other sauces, to lighten crème fraîche, make ice cream creamy, prevent chocolate from whitening, or distribute fat harmoniously. in the sausage meat.
Some germs become more aggressive
Valuable molecules for manufacturers. But this scientist’s research also shows that they are harmful to the billions of bacteria that make up our intestinal flora. “Our initial hypothesis was that these products promoted intestinal inflammation by degrading the layer of mucus which lines the wall of our intestines and protects it from microbiota bacteria,” says Benoît Chassaing. His hypothesis turned out to be correct – certain emulsifiers do promote inflammation – but not through the mechanism he initially imagined.
His team first studied polyphosphate 80 (P80) and carboxymethyl cellulose (CMC) in mice. Conclusion: these two emulsifiers push certain bacteria to pass through mucus. “CMC makes certain germs more aggressive, while P80 seems to weaken good bacteria,” summarizes Benoît Chassaing. The researcher then launched a small clinical study in humans, giving CMC to 16 volunteers for 15 days: “We were able to observe alterations in their microbiota compared to untreated subjects,” he reports.
But CMC and P80 are only two representatives of a family of additives which includes many others: lecithin, fatty acid esters, guar gum, xanthan gum… It was then that the microbiota in tubes became revealed to be valuable. Benoît Chassaing was able to use them to screen around twenty emulsifiers, among the most used. “Some were neutral, but most turned out to be just as harmful, or even more, than P80 and CMC. In particular carrageenans, which are very widely used,” he explains.
Inflammation, a risk factor for many diseases
With these results, his team was able to launch a larger-scale trial in humans. Some 150 patients suffering from Crohn’s disease (an inflammatory bowel disease) are being recruited. Half will follow a diet with few emulsifying agents, while the others will continue to eat “normally”. The objective: to see if a change in eating habits could improve patients’ symptoms.
To go further, scientists are also seeking to better understand the mechanisms at work. “From our first work on the effects of CMC and P80, we want to look more broadly at which bacteria respond to the presence of these compounds, which antigens they express, which are recognized by the receptors on the surface of our intestines, where they will induce and nourish inflammation,” explains the scientist. Enough to begin to lift a corner of the veil on the links between diet and chronic diseases, which have fascinated this researcher since the start of his career. “Chronic intestinal inflammation can then have consequences throughout the body, and can represent an additional risk factor in cardiovascular diseases, for example. This is in any case a hypothesis that we want to test,” explains Benoît Chassaing.
No scientist today imagines that food additives can trigger pathologies on their own. On the other hand, they could contribute to it, by adding to other negative elements. “In mice with genetic predispositions to inflammatory bowel diseases, the consumption of these emulsifying agents leads to an increase in the number of severe colitis. But even when the rodents do not have particular genetic predispositions, these compounds induce mild intestinal inflammation which proves sufficient to cause severe metabolic dysregulation”, continues Benoît Chassaing.
Above all, these products are rarely consumed alone. Thanks to the Nutrinet-Santé cohort managed by the nutritional epidemiology team of Professor Mathilde Touvier at Sorbonne Paris Nord University, scientists will be able to identify the most common cocktails of additives, and test their effects. The discoveries are only just beginning.
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