Microplastics are everywhere. In thewater, In the air, in the floors and even in our foodThis omnipresence poses a proven risk to human health, as our bodies eventually absorb these pollutants, with potentially disastrous consequences. Recently, for example, it has been shown that the brains of people with dementia have... higher concentrations of microplasticshighlighting a worrying correlation. These potentials health impacts They also concern cardiovascular diseases, as well as inflammatory or immune pathologies, although it is difficult at the moment to conclude with certainty on a mechanism or any causal link.
One of the ways in which these molecules could influence health is through the microbiota intestinal health, which is disrupted by this pollution. A new study has just confirmed this effect, emphasizing an important point: the impact of microplastics depends in part on their concentration and individual dietary habits. This discovery, made by researchers at the Toxalim Food Toxicology Laboratory of the University of Toulouse, was published on November 14, 2025, in the journal Environmental Science Nano.
The effect of microplastics studied in relation to diet
Despite the ubiquity of microplastics, it is likely that most of those that enter our bodies do so through our food (including water and beverages). Researchers have therefore focused particularly on the impact of these pollutants on the health of the digestive system. They concentrated on polystyrene nanoplastics (microplastics smaller than 1 μm) (used in food packaging), specifically to see if they disrupt the gut microbiota or the integrity of the intestinal barrier, depending on the individual's diet.
Male mice were exposed for 90 days to water containing different concentrations of these nanoplastics (0.1, 1, or 10 mg/kg daily), while following a normal diet or a diet high in sugar and fat (representing the "Western" diet). To track these plastic particles, they were combined with gold, which is easier to detect.
More pronounced effects were observed in mice fed a "Western" diet…
Unsurprisingly, mice fed a "Western" diet gained more weight. But this weight gain was even more pronounced in mice that consumed nanoplastics (at a concentration of 1 mg/kg). Yet, these animals did not eat more than those protected from this exposure, so the additional weight gain was not caused by an increased appetite. Surprisingly, this effect was not observed with the highest concentration of nanoplastics (10 mg/kg).
This impact, more pronounced in mice following this high-fat and high-sugar diet, was also visible at the level of intestinal immune defenses: the activity of lysozyme, an important protein in the defense against bacterial infections, decreased by almost half in those with nanoplastic concentrations of 1 or 10 mg/kg.
None of the studied concentrations caused increased intestinal barrier permeability, and these nanoplastics were not observed in organs other than the intestines. However, the lowest concentrations (0.1 and 1 mg/kg) affected the expression of genes involved in this permeability, altering intestinal epithelial cells, particularly in mice fed a high-sugar, high-fat diet. It is therefore possible that the study duration was too short and that these cellular-level changes could eventually weaken the intestinal barrier with longer exposure.
… except for the microbiota
The microbiota was affected by exposure to nanoplastics, but paradoxically, this effect was more pronounced in mice fed a healthy diet. Indeed, the lowest concentration (0.1 mg/kg) caused a significant decrease in microbiota diversity in these mice, whereas this decrease in diversity was less marked in mice fed a "Western" diet. This paradox could be explained by the effect of diet, which is known to alter the microbiota and reduce its diversity. It is therefore possible that the baseline level in these mice is already that of a degraded microbiota, where nanoplastics can no longer cause as much harm as in mice with a healthy microbiota.
A second paradox is that the negative effects of nanoplastics have been observed primarily at low concentrations, and rarely at high concentrations. The authors believe this is due to the aggregation of these molecules: the more concentrated they are, the more they will aggregate. These aggregates could travel more quickly through the intestinal tract and interact less with its surface, thus mitigating its biological effects. The researchers therefore emphasize the importance of considering microplastic concentrations in studies on their health effects. They also note that their research only included male mice, and therefore further studies will be needed to confirm these effects in females. Many questions remain about the health effects of microplastics, but the emerging picture is worrying.
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