Common food additive messes with gut bacteria

A widely used food additive, carboxymethylcellulose, alters the intestinal environment of healthy people, perturbing levels of beneficial bacteria and nutrients, a new study shows.

The findings, published in the journal Gastroenterology, demonstrate the need for further study of the long-term impacts of this food additive on health.

“It certainly disproves the ‘it just passes through’ argument…”

Carboxymethylcellulose (CMC) is a synthetic member of a widely used class of food additives, termed emulsifiers, which are added to many processed foods to enhance texture and promote shelf life.

Researchers have not extensively tested CMC in humans but the additive has been increasingly used in processed foods since the 1960s. It had long been assumed that CMC was safe to ingest because it is eliminated in the feces without being absorbed.

However, increasing appreciation of the health benefits provided by bacteria that normally live in the colon, and thus would interact with non-absorbed additives, has led scientists to challenge this assumption.

Experiments in mice found that CMC, and some other emulsifiers, altered gut bacteria resulting in more severe disease in a range of chronic inflammatory conditions, including colitis, metabolic syndrome, and colon cancer. However, the extent to which such results are applicable to humans had not been previously investigated.

The team performed a randomized controlled-feeding study in healthy volunteers. Participants, housed at the study site, consumed an additive-free diet or an identical diet supplemented with carboxymethylcellulose (CMC).

Because the diseases CMC promotes in mice take years to arise in humans, the researchers focused on intestinal bacteria and metabolites. They found that CMC consumption changed the make-up of bacteria populating the colon, reducing select species. Furthermore, fecal samples from CMC-treated participants displayed a stark depletion of beneficial metabolites that are thought to normally maintain a healthy colon.

Lastly, the researchers performed colonoscopies on subjects at the beginning and end of the study and noticed that a subset of subjects consuming CMC displayed gut bacteria encroaching into the mucus, which has previously been observed to be a feature of inflammatory bowel diseases and type 2 diabetes.

Thus, while CMC consumption did not result in any disease per se in this two-week study, collectively the results support the conclusions of animal studies that long-term consumption of this additive might promote chronic inflammatory diseases. Therefore, further studies of this additive are warranted.

“It certainly disproves the ‘it just passes through’ argument used to justify the lack of clinical study on additives,” says senior author Andrew Gewirtz of Georgia State University.

Beyond supporting the need for further study of carboxymethylcellulose, the study “provides a general blueprint to carefully test individual food additives in humans in a well-controlled manner,” says co-senior author James Lewis, of the University of Pennsylvania, where the subjects were enrolled.

Such studies need to be large enough to account for a high degree of subject heterogeneity, says lead author Benoit Chassaing, research director at INSERM, University of Paris. “Indeed, our results suggest that responses to CMC and likely other food additives are highly personalized and we are now designing approaches to predict which individuals might be sensitive to specific additives.”

Additional authors are from Penn State University and the Max Planck Institute. The National Institutes of Health, the European Research Council, the Max Planck Society, the INSERM, and the Kenneth Rainin Foundation funded the work.

Source: Georgia State University

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