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CMC’s impact on gut health comes under increasing scrutiny

Carboxymethylcellulose (CMC) has been associated with gut dysbiosis. Should food and supplement manufacturers be concerned?

Often labelled as E 466, “cellulose gum”, or “sodium carboxymethyl cellulose”, CMC is a versatile inactive ingredient that can serve as a thickener, binder, disintegrant, stabiliser, and suspending agent.

In capsules and tablets, CMC is used as both a binder to hold powder mixtures together and a disintegrant to enhance bioavailability.

It is added to protein powders to promote a smooth, creamy mouthfeel and to prevent active ingredients from clumping or separating. In gel formats it helps control moisture retention and maintain a consistent texture.

And in liquids and syrups, it increases viscosity and keeps active nutrients evenly suspended in solution.

With such a broad spectrum of functionality, it is not surprising that CMC is ubiquitous in foods and supplements. The list of brands that use the ingredient is long and includes some of the most reputable and established names in health supplements and sports nutrition: Ensure, Solgar, Vitabiotics, Nature’s Best, Woods Supplements, and Lamberts Healthcare, to name but a few.

And, given that CMC is recognised as safe by the European Food Safety Authority (EFSA) and the US Food and Drug Administration (FDA), there is no reason why they shouldn’t.

However, in recent years there has been growing unease around the industry’s use of CMC, following research that suggests it may disrupt the gut microbiota and impact gastrointestinal health.

Research reports gut microbiome altering effects

Critics of CMC often cite a 2022 controlled feeding study as evidence of the dangers of the additive.

In this study, the researchers found that addition of CMC to a healthy, additive-free diet increased postprandial abdominal discomfort and altered intestinal microbiota composition.

In addition, CMC consumption was found to starkly impact the faecal metabolome, which included depletion of health-promoting metabolites such as short-chain fatty acids and free amino acids.

Some individuals also displayed microbiota encroachment into the normally sterile inner mucus layer following CMC consumption.

“These results support the notion that the broad use of CMC in processed foods may be contributing to increased prevalence of an array of chronic inflammatory diseases by altering the gut microbiome and metabolome,” the researchers wrote in the journal Gastroenterology.

Challenging food safety assessment frameworks

This research challenges the very premise on which food safety agencies have historically considered CMC safe – namely, that as a derivative of natural cellulose, it passes through the gastrointestinal tract unabsorbed.

It has prompted the scientific community to call for reconsideration of current food safety assessment frameworks to better account for microbiota-related outcomes.

Some food and supplement manufacturers have taken an anti-CMC stance on the back of these findings, making it publicly known that their products do not contain CMC. Nutrimuscle, for example, guarantees the absence of CMC in its nutritional supplements.

In a blog on its website, it states that as a result of this policy, “Nutrimuscle native whey foams more than CMC-modified whey, but the consumer does not take any unnecessary health risks”.

But is the removal of CMC from foods and supplements justified and necessary?

Bringing balance to the discussion

Professor Roberto Cannataro, a sports science lecturer at the University of Calabria who holds a bachelor’s degree in food technology and a master’s degree in chemical engineering, weighed up the evidence.

“The effect in humans has only been reported in three studies. One of these is a case report that relates to allergies, one is very old, and the other [the 2022 Gastroenterology study] is the only one worth considering,” he told Ingredients Network.

He said that while there have been a number of studies on animals and cells that could give insights into CMC’s effect on gut health, these should just be viewed as “a first step”.

“It is worth remembering that the microbiota of a rat or a mouse is quite different to that of a human and that the mechanism behind the outcome has not been clarified or hypothesised,” he added.

Cannataro expressed other concerns about blacklisting CMC on the basis of currently available evidence.

“Another difficulty is that whereas blood samples are representative of a person’s blood, with stool samples, which are used in gut microbiota analysis, there is more variation, which can influence results. So when we talk about microbiota, we have to be careful that we are drawing definitive conclusions,” he said.

A logical theory

Nevertheless, Cannataro accepts that at a molecular level, the theory that CMC disrupts the microbiota is rooted in logic.

CMC is a water-soluble polysaccharide that is produced via chemical modification of cellulose. With this modification, it acquires new physicochemical and functional properties – and, according to Cannataro, this modification could be responsible for the effects that researchers are seeing.

“We have to consider that we are introducing a fibre that is different from the cellulose that is naturally occurring in fruit and vegetables. We are designed to have cellulose in our gut. Even if we don’t digest it directly, some of the bacteria in the gut can ferment it, and the modification of cellulose into CMC could influence the microbiota,” he explained.

“In short, cellulose normally has a positive effect – but as CMC is a modified form of cellulose, it probably doesn’t have a positive effect.”

So why not just use cellulose in its natural form? The answer is that it is not as commercially attractive as CMC.

“Cellulose works, but it usually results in a shorter shelf life,” he said.

While at present there is no widespread push to outlaw CMC, anecdotal evidence suggests pressure is building.

“At the moment I am not seeing a decline in the use of CMC, but I am seeing the scientific community paying an increasing amount of attention to CMC, which means that in the next three to five years, this will probably filter through to the food industry,” Cannataro said.

With this in mind, he would like to see more human studies being performed, with the aim of characterising the mechanism responsible for CMC’s reported effect on the composition and function of the gut microbiota.