Food additives can be worrisome, especially when you don’t know what they are and why they are in your food. Seeing carboxymethylcellulose — CMC — in an ingredient list can be downright alarming. It turns out that you are right to be concerned about CMC. New research suggests it may be a factor contributing to a number of gastrointestinal problems.

There are about 2,800 substances used as food additives. The most common are salt, sugar and corn syrup. Added to packaged and processed foods, additives add flavor, keep foods fresh longer and help keep them from spoiling.

The results call into question the idea that CMC just passes through the GI tract and poses no harm. It may well disrupt the intestinal microbiota and encourage inflammation.

Consumption of processed foods has increased considerably over the past 60 years. At the same time, the incidence of chronic inflammatory diseases has also increased, suggesting that something present in processed foods could be promoting inflammation.

Carboxymethylcellulose (CMC), or cellulose gum, is a synthetic food additive that acts as an emulsifier. Emulsifiers keep oils and fats from separating, and they are approved by the Food and Drug Administration (FDA). Their purpose is to keep foods thick and creamy, help retain moisture in foods and increase the shelf life of products. Many prepackaged and processed foods such as margarine, ice cream, salad dressings, mayonnaise, chocolate, peanut butter, baked goods and ice cream contain emulsifiers.

The emulsifier has been added to food since the 1960s. It is under-studied; but despite a lack of extensive testing on its safety, it is on the FDA’s GRAS list — generally recognized as safe. It has always been assumed to be safe because it passes through the gastrointestinal tract and leaves the body in a person’s feces,.

But recent research has called the safety of CMC into question. Even though it is not absorbed by the body, it appears it may interact with good bacteria in the colon as it passes through and cause harm, researchers now believe. For example, research on mice has found that many emulsifiers, including CMC, changed the gut bacteria and led to conditions including colitis, metabolic syndrome and colon cancer.

To build on that research, scientists from the University of Pennsylvania, University of Georgia and the National Institute of Health and Medical Research in France looked at how CMC might affect human health. A group of 16 healthy volunteers lived at a testing site for two weeks and ate either a diet of additive-free foods or the same diet with added CMC.

The incidence of chronic inflammatory diseases like colitis has increased in step with our consumption of processed foods.

Because the damage emulsifiers cause in mice would take years to see in humans, the scientists studied the balance of intestinal bacteria and metabolites in the study’s participants.

CMC reduced the diversity of bacteria in the colon, decreasing the number of beneficial bacteria that support human health. Fecal samples from people consuming CMC showed they had significantly lower numbers of the metabolites that maintain the health of the colon.

Participants had colonoscopies before and after the experiment. These showed that some of the participants whose diets contained CMC had gut bacteria approaching the normally sterile inner mucus area of the stomach, a key warning sign of type 2 diabetes and inflammatory bowel diseases such as Crohn’s disease and ulcerative colitis.

The results call into question the idea that CMC safely passes through the GI tract and poses no harm. It may well disrupt the intestinal microbiota and encourage inflammation. While the study focused only on one food additive, these results should encourage research into the effect of other emulsifiers on human health.

The study is published in Gastroenterology.