Those cellulose-based thickeners in everyday foods like ketchup, salad dressing and even toothpaste were once thought to pass through the body unchanged. But new research from the University of British Columbia shows your gut microbes may be breaking them down after all.
These additives are widely used to improve texture and stability in products such as sauces, ice cream, plant-based milks, baked goods, snack bars and processed meats.
The study, published in the Journal of Bacteriology, found that artificial cellulose derivatives can be digested by certain gut bacteria if the microbes have first been exposed to natural plant fibers, or polysaccharides, from fruits, vegetables and cereals.
“Researchers assumed that these thickening agents, which are artificial derivatives of natural cellulose, just pass right through the digestive system unaltered,” said lead author Dr. Deepesh Panwar, a postdoctoral fellow at UBC’s Michael Smith Laboratories. “But our study provides a first glimpse at how these food additives are actually digested by our gut bacteria thanks to natural polysaccharides in our diets.”
Cellulose derivatives resist breakdown for the same reason they work so well in foods. Their complex structure makes them stable and, in higher concentrations, useful in laxatives. In lab experiments, when bacteria were exposed to both cellulose derivatives and natural plant fibers, they produced enzymes capable of breaking down both, releasing sugars the microbes could use as fuel.
“It was really unexpected for us to see that these cellulose derivatives are in fact used as a source of sugar for bacterial growth,” said co-author Dr. Harry Brumer, a professor in UBC’s Department of Chemistry. “It is always a surprise when a new finding goes against the conventional wisdom.”
These additives remain safe to consume, with decades of use behind them. The findings raise new questions about how diet influences their digestion and what this might mean for gut health. The research team will next explore whether this process occurs in a broader range of gut bacteria and the potential effects on human nutrition.
For now, if you eat cellulose-thickened foods along with fiber-rich plants, your gut bacteria may be breaking down more than you realize.
This research was funded by the Canadian Institutes of Health Research, the Natural Sciences and Engineering Research Council of Canada, and Bioindustrial Innovation Canada.