A commonly used food additive is believed to alter the human gut microbiota and environment

Given the high prevalence of chronic inflammatory bowel diseases, such as Crohn’s disease, research is progressing to better identify the risk factors of these diseases and thus improve patient management. Scientists at the Cochin Institute (Inserm/CNRS/the University of Paris), led by Inserm researcher Benoît Chassaing, had shown in mice that the presence of food emulsifiers in many processed foods could promote inflammation in the intestine. In a new study, published in Gastroenterology, the same team now shows in healthy volunteers that carboxymethylcellulose (CMC)[1], a widely used food emulsifier, impacts the intestinal environment by altering the composition of the microbiota. The team emphasizes the need for further work to characterize the long-term impact of this food additive, as well as studies in individuals with chronic inflammatory bowel disease.

Nearly 20 million people worldwide are thought to be affected by chronic inflammatory bowel disease, including Crohn’s disease and ulcerative colitis. Genetic factors have been identified to explain the inflammation of the intestine that characterizes these diseases, but these predispositions are not sufficient to explain the occurrence of these diseases. Thus, for several years, many research teams have been looking at environmental factors.

This is the case of Inserm researcher Benoît Chassaing and his team at the Cochin Institute (Inserm/CNRS/University of Paris) who are interested in the impact of food – and more specifically the role of certain food additives, such as emulsifiers – on the intestinal microbiota.

In particular, the team has studied the impact of carboxymethylcellulose (CMC), a synthetic emulsifier added to many processed foods to improve texture and extend shelf life. Previous work in mice has shown that CMC, along with some other emulsifying agents, alters the composition of the gut microbiota and thus leads to the aggravation of many chronic inflammatory diseases, such as colitis, metabolic syndrome, and colon cancer.

In new work, scientists, therefore, sought to verify whether CMC could have the same impact on humans because, although it has never been extensively clinically tested, this molecule has been increasingly used in processed foods since the 1960s.

Clinical study on healthy volunteers

To conduct the clinical study, scientists recruited a small group of healthy volunteers. The participants were housed at the study site for the duration of the study and were divided into two groups. One group ate a strictly controlled diet with no additives, and the other a diet supplemented with CMC.

After two weeks, the researchers observed that the composition of bacteria in the gut of the participants consuming CMC was altered, with a net decrease in the number of certain species known to play a beneficial role in human health, such as Faecalibacterium prausnitzii. In addition, the fecal samples of participants receiving CMC were severely depleted for many beneficial metabolites. Finally, clinically, these participants were more prone to abdominal pain and intestinal bloating.

Colonoscopies performed on these volunteers at the beginning and end of the study also showed that a subgroup of subjects in the CMC consumption group had intestinal bacteria located closer to the intestinal walls. This is a characteristic observed in inflammatory bowel diseases and type 2 diabetes.

While CMC consumption did not result in any inflammatory pathology in this relatively short study, these results confirm data from animal studies and suggest that long-term consumption of this additive may negatively impact the gut microbiota and therefore promote chronic inflammatory diseases and metabolic dysregulations in humans.