At a Glance
- Researchers discovered that certain human gut bacteria can metabolize artificial cellulose derivatives, additives commonly found in processed foods and previously thought to be completely indigestible.
- This metabolic process is triggered when the bacteria are first exposed to natural plant fibers, which activate enzymes capable of breaking down the synthetic cellulose compounds.
- The in vitro study focused on specific gut bacteria from the Bacteroidota phylum, demonstrating that this ability is dependent on both the bacterial strain and the specific type of plant fiber.
- These findings challenge the long-held conventional wisdom that soluble cellulose derivatives pass through the digestive system of monogastric animals without being altered or used.
- While the additives remain safe, this discovery prompts further investigation into the broader physiological effects of their metabolism by the gut microbiota in the context of a balanced diet.
In a groundbreaking discovery, scientists have found that common food additives once believed to be indigestible can be broken down by bacteria living in the human gut. New research from the University of British Columbia, published in the Journal of Bacteriology, reveals that certain gut microbes can metabolize synthetic cellulose derivatives—thickening agents found in products ranging from ketchup to toothpaste—but only when activated by natural dietary fiber.
These additives, such as carboxymethyl cellulose (CMC), are large molecules called polysaccharides, which are long chains of sugars. Their complex structure makes them effective thickeners, but it was also thought to prevent our gut bacteria from using them as food. The new laboratory study, however, shows that when gut bacteria are first “primed” with natural polysaccharides from fruits, vegetables, and cereals, they produce enzymes on their cell surfaces. These enzymes, designed to break down natural fibers, also have the unexpected ability to break down artificial cellulose molecules, allowing the bacteria to consume them.
“It was really unexpected for us to see that these cellulose derivatives are in fact used as a source of sugar for bacterial growth,” says Dr. Harry Brumer, a professor at the Michael Smith Laboratories and a senior author of the study in a university press release. Researchers may have missed this interaction previously because lab experiments often test compounds in isolation, unlike the complex mix of foods in a typical human diet. On their own, the cellulose derivatives could not trigger the enzyme activity, leaving them undigested.
While the findings do not challenge the established safety of these common additives, they open up new avenues for research. The study counters the long-held assumption that these substances are inert and pass through the digestive system without being absorbed. Scientists now plan to investigate this ability in a broader range of gut bacteria and explore the potential effects this newfound metabolism could have on human nutrition and overall gut health.
References
- Panwar, D., Stewart, W. A., Rodd, A., & Brumer, H. (2025). Artificial cellulose derivatives are metabolized by select human gut Bacteroidota upon priming with common plant β-glucans. Journal of Bacteriology, e00198-25. https://doi.org/10.1128/jb.00198-25
- University of British Columbia. (2025, August 12). Common food thickeners—Long thought to pass right through us—Are actually digested. Phys.Org; University of British Columbia. https://phys.org/news/2025-08-common-food-thickeners-thought-digested.html
