The Food Additive That Blocked Diet-Driven Colitis in Mice

If you've ever wondered whether the invisible ingredients in processed food are shaping your gut health, a new mouse study gives one of the most detailed answers yet, tracing a single food additive all the way from the dinner plate to the inside of an immune cell's mitochondria. Researchers at Sichuan University found that carboxymethylcellulose (CMC), a thickening agent used in everything from ice cream to salad dressing, blocked the colon inflammation that a high-fat diet normally triggers in mice, and they mapped out exactly why. The result adds a new twist to a genuinely contested question: does this common additive protect the gut, or damage it? The honest answer, based on this study and the research it sits alongside, is that it may depend on the diet it's added to and the person eating it.

Key takeaways

• In mice, the common food thickener carboxymethylcellulose (CMC) reversed high-fat-diet-driven colon inflammation, cutting a bile-acid-producing gut bacterium by roughly 18-fold and the harmful bile acid itself by about 28-fold.
• The protection required restoring a specific energy-producing function (mitochondrial complex I) inside immune cells called macrophages; mice engineered to lack it in those cells got no benefit from CMC at all.
• A companion survey of 71 human ulcerative colitis patients found higher dietary fat intake correlated with worse disease activity during active flares, but correlation is not causation.
• This is an unreviewed preprint, and CMC's effects on gut health are genuinely contested elsewhere in the literature. Don't change your diet based on this study alone.

Carboxymethylcellulose Blocked High-Fat-Diet Colitis in Mice

In mice, adding carboxymethylcellulose (CMC), a widely used food emulsifier and thickener, to drinking water reversed the colon damage caused by a high-fat diet, cutting inflammation scores, preserving colon length, and repairing the gut's protective lining, according to a preprint posted on Research Square by a team at Sichuan University's West China Hospital. The researchers first confirmed the problem CMC was solving: mice fed a high-fat diet (39% of calories from fat) developed markedly worse colitis after a standard chemical colitis trigger than mice on regular chow, with more tissue damage, higher disease-activity scores, and a breakdown in the gut's lining protein. That worsening tracked with a spike in deoxycholic acid (DCA), a secondary bile acid that gut bacteria produce by chemically modifying the bile the liver sends out to digest fat, a molecule separately linked to inflammatory activity in the colon in other mouse research. When the researchers added CMC to the mice's drinking water for four weeks before triggering colitis, DCA levels in the colon dropped by roughly 28-fold, and the colitis mostly disappeared.

Why This Matters for People With Ulcerative Colitis

This research centers on ulcerative colitis (UC), a chronic inflammatory bowel disease that inflames and ulcerates the lining of the large intestine and typically first appears between ages 15 and 30. Diet is a prime suspect in why UC rates have risen alongside Western eating patterns, and this study adds human data to that picture: the researchers surveyed the diets of 71 UC patients, split roughly evenly between those with active disease and those in remission, and found that in patients with active UC, higher dietary fat intake correlated with a higher Mayo score (a standard severity measure, r = 0.35, P = 0.04) and a higher erythrocyte sedimentation rate (a blood marker of inflammation, r = 0.60, P = 0.03). No such link showed up in patients whose disease was in remission. For anyone managing UC, Crohn's disease, or another IBD, this reinforces that fat intake is worth discussing with a gastroenterologist, even though this dataset cannot prove fat caused the flares.

How Researchers Traced Diet to Bacteria to Mitochondria

The team built its case for how CMC works through a chain of experiments designed to rule out simpler explanations first. They ruled out CMC directly altering fat itself, using a chemical imaging technique that showed no change in fat molecule structure when the two were mixed. They ruled out CMC directly binding DCA in the gut, since giving mice CMC alongside DCA enemas produced no protective effect. That left the gut microbiome: gene sequencing of the mice's gut bacteria showed CMC cut the abundance of a species called Bacteroides acidifaciens by roughly 18-fold. That species carries an enzyme that converts the liver's primary bile acids into secondary bile acids like DCA, and mice given live B. acidifaciens developed worse colitis than mice given a heat-killed version, confirming the bacterium's role. Finally, single-cell sequencing of colon tissue showed the diet-driven inflammation was concentrated in pro-inflammatory immune cells called macrophages, and lab experiments showed that high concentrations of DCA impaired a component of the macrophage's energy-generating machinery called mitochondrial complex I, while the lower DCA levels CMC produced restored it. The strongest evidence came from mice genetically engineered to lack complex I only in their immune cells: in those mice, CMC's protective effect against colitis disappeared entirely, showing that restoring this mitochondrial function was necessary for CMC's benefit. In a side comparison, CMC's protective effect was roughly comparable to cholestyramine, an existing bile-acid-binding drug.

What This Could Mean for Your Diet, and What It Doesn't

None of this makes carboxymethylcellulose a treatment. This is a mouse and cell-culture study; nothing here has been tested as an intervention in people with IBD, and no one should add or avoid CMC-containing foods based on it. What the mechanism does clarify is that context probably matters: in this model, CMC counteracted damage that a high-fat diet itself was causing, by lowering an excess bile acid the diet was driving up. That's a narrower claim than "CMC is good for the gut." If you're managing UC, Crohn's, or another gut-inflammation condition, the practical takeaway is that dietary fat and bile acid metabolism are a real, active research area worth raising with your care team, not that any specific additive is protective or harmful.

The Big Caveat: CMC's Effects on the Gut Are Genuinely Contested

This paper is a preprint: it was posted on Research Square on August 27, 2026, and has not yet been peer-reviewed, so its methods and conclusions have not been independently vetted by outside scientists. The paper's own introduction acknowledges that CMC has "controversial effects" in the existing colitis literature, sometimes worsening inflammation and sometimes easing it, depending on the model. That tension is real: a randomized controlled-feeding trial in healthy human volunteers found that eating CMC daily for 11 days reduced the diversity of participants' gut bacteria and modestly increased abdominal discomfort, the opposite direction from this new mouse result. The two studies aren't directly comparable, since this new work tested CMC specifically as a counter to high-fat-diet damage rather than as an addition to a normal diet, but the contradiction is a reminder that a food additive's effect on the gut can depend heavily on what else is happening in that gut at the time.

What Comes Next for This Bile-Acid Research

The researchers frame this as mechanistic groundwork, not a finished answer. The next steps would be peer review of the preprint itself, followed by studies testing whether the same bile-acid and mitochondrial pathway holds up in human gut tissue or a clinical trial, and work to reconcile why CMC looks protective against high-fat-diet colitis here while looking harmful to a normal, healthy gut microbiome elsewhere. No timeline for human testing was given in the preprint.

Common Questions

Is carboxymethylcellulose safe to eat? CMC is a widely approved food additive used as a thickener and stabilizer, but its effects on gut health remain an active research question, with different studies finding it protective or harmful depending on the underlying diet and health status of the person or animal eating it.

Does this study mean CMC treats ulcerative colitis? No. This is a preprint mouse and cell-culture study; CMC has not been tested as a treatment for ulcerative colitis or any other condition in humans, and no one should use it that way based on this research.

What is deoxycholic acid, and why does it matter here? Deoxycholic acid (DCA) is a secondary bile acid that gut bacteria produce from the primary bile acids the liver releases to digest fat; at high levels it has been linked to gut inflammation in other studies, and this research found a high-fat diet drives DCA levels up while CMC brought them back down.

Should people with IBD avoid high-fat diets? This study's human data found a correlation, not proof, between higher dietary fat intake and worse disease activity in patients with active ulcerative colitis; anyone with IBD should discuss diet changes with their gastroenterologist rather than self-adjust based on a single preclinical study.

References

1. Limei Shao, Linglong Ji, Wenle Liu, et al. (2026). Carboxymethylcellulose ameliorates high-fat diet-associated colitis through the reduction of deoxycholic acid and restoration of mitochondrial complex I in macrophages. https://doi.org/10.21203/rs.3.rs-9501242/v1
2. Shengnan Zhao, Zizhen Gong, Jiefei Zhou, et al. (2016). Deoxycholic Acid Triggers NLRP3 Inflammasome Activation and Aggravates DSS-Induced Colitis in Mice. Frontiers in Immunology. https://doi.org/10.3389/fimmu.2016.00536
3. Ulcerative Colitis – NIDDK. NIH. https://www.niddk.nih.gov/health-information/digestive-diseases/ulcerative-colitis