A year gluten-free changes your microbiome, but not all the way back to normal

If you were told to go gluten-free after a celiac diagnosis, you probably assumed that once the diet "worked," your gut would go back to normal. A new study used MRI scans and stool DNA testing to actually check that assumption in people newly diagnosed with celiac disease, tracking them for a full year on a gluten-free diet. The answer is more complicated than "problem solved": gut function and the gut microbiome (the community of bacteria living in the digestive tract) both improved, but neither fully caught up to healthy volunteers.

Key takeaways:

• Newly diagnosed celiac patients had more fluid in the small bowel and slower gut transit than healthy people before starting treatment.
• After a year of gluten-free eating, some of these differences improved, but the study found the gut and its microbiome still had not fully matched healthy controls.
• The findings, from a small but carefully matched study, point toward developing microbiome- or prebiotic-based add-on treatments alongside the diet, though nothing like that is proven yet.

MRI Study Tracks Gut Function in Celiac Disease

Researchers from the University of Nottingham and the Quadram Institute, in a study led by radiographer Dr. Carolyn Costigan and gastrointestinal imaging specialist Prof. Luca Marciani, used MRI to directly measure how the gut behaves in people newly diagnosed with celiac disease (an autoimmune condition in which eating gluten damages the lining of the small intestine). Called the MARCO study, the project compared 36 newly diagnosed celiac patients against 36 healthy volunteers matched for age, sex, and body mass index (BMI), scanning and sampling both groups at the start of the study and again after 12 months. At baseline, before treatment began, patients with celiac disease reported more gut symptoms and showed higher small bowel water content (SBWC, the amount of fluid sitting in the small intestine, measured by MRI) and slower whole-gut transit time (WGTT, how long it takes food to move through the entire digestive tract) than the matched healthy group.

Why Celiac Patients and Anyone With Gut Symptoms Should Care

Celiac disease triggers an abnormal immune reaction to gluten, a protein in wheat, barley, and rye, and the standard treatment is a strict, lifelong gluten-free diet. For most patients, that diet is expected to resolve symptoms and let the gut heal. This study matters because it is one of the few to combine objective imaging with microbiome sequencing to check whether "feeling better" on the diet actually means the gut has returned to normal function, rather than relying on symptom questionnaires alone. That distinction matters for anyone managing celiac disease, or symptoms that overlap with irritable bowel syndrome (IBS), since ongoing bloating or irregular transit after going gluten-free is not necessarily "in your head" or a sign you are doing the diet wrong.

Inside the Design: MRI Plus Metagenomic Sequencing

Beyond MRI measurements of small bowel water content, whole-gut transit time, and colon volume, the researchers ran shotgun metagenomic sequencing on stool samples from both groups. This method reads the genetic material of all the bacteria in a stool sample, identifying which species are present and what functional genes they carry, including CAZymes (carbohydrate-active enzymes, the bacterial tools used to break down dietary fiber). Sequencing was done at baseline and again at the 12-month mark, letting the team track how the gut microbiome shifted over the same year that gut physiology was being measured by MRI, in the same 36 patients.

What a Year Gluten-Free Actually Changes, and What It Does Not

Over the 12 months on a gluten-free diet, both gut physiology and microbiome composition shifted in the celiac patients, and the researchers describe the diet as improving some, but not all, of the parameters that had differed from healthy controls at baseline. In practical terms, that means a reader who has been strictly gluten-free for a year and still has occasional bloating, irregular bowel habits, or other lingering gut symptoms is describing something this study actually detected on imaging, not something that indicates the diet has failed. It is not evidence that any specific probiotic, prebiotic, or supplement fixes the gap. The researchers frame their findings as support for future work on microbiome-targeted treatments to sit alongside the gluten-free diet, not as proof that any such treatment already works. This finding is consistent with other research showing that a gluten-free diet raises the diversity of gut bacteria in celiac patients back up, but the resulting mix of bacteria still looks different from a healthy person's microbiome, rather than being a simple restoration.

Limitations Worth Knowing Before You Read Too Much Into This

The study followed 36 celiac patients and 36 matched healthy controls, a modest sample drawn from a single center in the UK, and it is observational: it shows that gut function and microbiome changes occurred alongside the gluten-free diet, not that the diet alone is definitively the cause of every change measured, since other lifestyle factors could not be fully ruled out. The work also grew out of a PhD research project, which does not undermine the findings but is worth knowing as context. Larger, multi-center studies would be needed to confirm how consistent these patterns are across different populations.

What Comes Next for Celiac Gut Research

The authors point toward the next logical step: testing whether microbiome-targeted or prebiotic add-on treatments, used alongside a standard gluten-free diet, can close the gap between celiac patients and healthy controls faster or more completely than diet alone. No timeline for such trials has been announced, and no specific product or supplement has been tested in this study. For now, the gluten-free diet remains the only established treatment for celiac disease.

Common Questions

Does a gluten-free diet fully repair the gut in celiac disease? Not according to this study. After 12 months, gut function and microbiome composition had improved but had not fully matched healthy controls.

What is small bowel water content and why does it matter? It is the amount of fluid measured inside the small intestine using MRI. Higher fluid levels at baseline suggested altered gut function in newly diagnosed celiac patients.

Should I try a probiotic or prebiotic if I still have symptoms on a gluten-free diet? This study did not test any probiotic or prebiotic and does not establish one as effective. It only points to microbiome-targeted treatments as a direction for future research.

How large was this study? It compared 36 newly diagnosed celiac patients with 36 matched healthy volunteers at a single UK center, followed from diagnosis through 12 months on a gluten-free diet.

References

1. Carolyn M. Costigan, Frederick J. Warren, Anthony P. Duncan, et al. (2025). One Year of Gluten-Free Diet Impacts Gut Function and Microbiome in Celiac Disease. Clinical Gastroenterology and Hepatology. https://doi.org/10.1016/j.cgh.2024.11.006
2. Definition & Facts for Celiac Disease – NIDDK. NIH. https://www.niddk.nih.gov/health-information/digestive-diseases/celiac-disease/definition-facts
3. Treatment for Celiac Disease – NIDDK. NIH. https://www.niddk.nih.gov/health-information/digestive-diseases/celiac-disease/treatment
4. Orazio Palmieri, Stefano Castellana, Antonio Bevilacqua, et al. (2022). Adherence to Gluten-Free Diet Restores Alpha Diversity in Celiac People but the Microbiome Composition Is Different to Healthy People. Nutrients. https://doi.org/10.3390/nu14122452