The Microbiome Research group at the Vall d’Hebron Research Institute (VHIR) has identified mechanisms that explain how diet influences the gut microbiota and inflammation in Crohn’s disease and ulcerative colitis. The results, published in Gut, show that diet modulates the microbiota differently in the two diseases, leading to differences in intestinal inflammatory processes.

Inflammatory bowel disease (IBD) is a group of conditions that cause swelling and inflammation of the tissues of the digestive tract. The most common are ulcerative colitis and Crohn’s disease. Although they share similar symptoms (abdominal pain, diarrhoea, rectal bleeding, weight loss, extreme fatigue, etc.), the pattern of involvement differs. While ulcerative colitis causes ulcers in the lining of the colon and rectum, Crohn’s disease affects the deeper layers of the digestive tract and, more commonly, the small intestine.

Diet and the gut microbiota play an important role in the development of these conditions. “Changes in the microbiota are associated with alterations in the immune system, but the specific mechanisms through which certain microorganisms contribute to this process remain unknown. With this work, we aim to understand the mechanisms of IBD and the differences between Crohn’s disease and ulcerative colitis, as well as the role of diet in these processes”, explains Dr. Chaysavanh Manichanh, head of the Microbiome Research group at VHIR and researcher in the CIBER area of Digestive and Liver Diseases (CIBEREHD).

The role of diet in modulating inflammation

The study analysed nearly 200 individuals, including patients with Crohn’s disease, patients with ulcerative colitis and healthy controls. The team assessed participants’ usual diet and related it to the composition and function of their gut microbiota, as well as to clinical and biochemical markers of inflammation.

The results confirm that patients with IBD have poorer diet quality, which is associated with changes in the gut microbiota. For example, they show lower bacterial diversity, particularly in Crohn’s disease. This diversity increases with diets rich in fibre, fruit, vegetables and nuts, and decreases with higher consumption of processed foods and sugar-sweetened beverages.

In addition, the study demonstrates that microbiota alterations are linked to changes in the intestinal inflammation characteristic of the disease. However, the mechanisms connecting diet, microbiota and inflammation differ according to the type of IBD. “In Crohn’s disease, we observed that certain foods and dietary patterns induce changes in specific bacteria and metabolic pathways, which are associated with inflammation”, notes Dr. Luis Mayorga, specialist at the Digestive System Department of Vall d’Hebron University Hospital and researcher in the Microbiome Research group at VHIR. “By contrast, in ulcerative colitis, the relationship between diet and inflammation seems to depend more on global changes in the microbiota, such as loss of diversity and functional imbalance”, he adds.

For example, in Crohn’s disease, healthier diets and the consumption of coffee or wholemeal bread are associated with the presence of specific bacteria and metabolites that reduce intestinal inflammation. In ulcerative colitis, adherence to a Mediterranean, fibre-rich diet reduces inflammation by maintaining gut bacterial diversity.

Studying the microbiota as a diagnostic biomarker for Crohn’s disease

In a complementary approach, the team analysed gut microbiota alterations in patients with Crohn’s disease and ulcerative colitis and identified a set of bacteria that could aid in disease diagnosis. They also examined how these changes are associated with intestinal inflammation. This study was published in Biomarker Research.

Faecal samples from 34 individuals with Crohn’s disease, 33 with ulcerative colitis and 67 healthy controls were analysed. Differences in microbiota among the three groups were studied using various techniques that identify the types of microorganisms present and their functions.

The results revealed marked alterations in the microbiota of patients with Crohn’s disease, with reduced bacterial diversity and abundance compared with healthy individuals. “We found that patients with Crohn’s disease show many more potentially harmful changes, such as an increase in pathogenic bacteria, for example Escherichia coli, and a reduction in beneficial bacteria”, says Gerard Serrano, predoctoral researcher in the Microbiome Research group at VHIR.

Specifically, a panel of 20 bacterial species was identified as useful for detecting Crohn’s disease, as they are characteristic of these patients. “Analysing this group of bacteria could be a non-invasive and cost-effective diagnostic tool, particularly useful in cases where endoscopy does not provide conclusive results”, highlights Dr. Manichanh.

Results that support personalised strategies for each patient

Taken together, both studies show that the gut microbiota is altered in inflammatory bowel disease and that these changes play an active role in diet-associated inflammatory mechanisms, as well as aiding patient diagnosis.

“These findings lay the groundwork for the future development of more personalised strategies that provide dietary recommendations based on microbiota changes and tailored to each patient”, concludes Dr. Manichanh.