The Mediterranean diet changed the gut microbiome and decreased the concentration of fecal calprotectin in patients with remission of ulcerative colitis

Oct 30, 2023 | Nutrition

Ulcerative colitis is a chronic inflammatory bowel disease that results in diffuse friability and superficial erosions of the colonic wall and associated bleeding. Characteristically, it involves inflammation restricted to the mucosa and submucosa of the colon. The specific cause is not known, but autoimmunity may also play an important role in the etiology of ulcerative colitis. It was also suggested that the pathogenesis of this inflammatory bowel disease is correlated with gut microbiome changes. Therefore, nutritional patterns are important in ulcerative colitis treatment. In this study, the Canadian researchers compared the effects of the Mediterranean diet and the Canadian habitual diet on the gut microbiome and ulcerative colitis activity in patients with remission of ulcerative colitis.

Previous studies have demonstrated a lack of diversity and general instability of the gut microbiome in ulcerative colitis, frequently accompanied by a dysbiosis characterized by the relative depletion of Faecalbacterium praustnitzii and Roseburia hominis and the enrichment of Escherichia coli, Ruminococcus torques, and R. gnavus.

The Mediterranean diet is characterized by increased consumption of legumes, whole grains, vegetables, fruits, nuts, seeds, and olive oil, moderate consumption of fish, poultry, and dairy foods, and low consumption of processed foods and red meat. High levels of dietary fiber, phytochemicals, and fat blend (high monounsaturated fat) have beneficial anti-inflammatory and antioxidant properties.

About the study

This prospective, randomized, controlled study included 28 adults who had mild to moderate ulcerative colitis and were in remission. Participants were randomly assigned to either a Mediterranean diet (n = 15) or a Canadian habitual diet (n = 13) for 12 weeks. They were on a stable dose of ulcerative colitis therapy without any dosage adjustments for two months before starting the study for those who were taking oral 5-aminosalicylates, thiopurines, or methotrexate, or for three months before starting the study for those who were taking infliximab or adalimumab. The median age of the participants was 47 years (ranging 18-65 years)

The Simple Clinical Colitis Activity Index (SCCAI) and the Partial Mayo Score were used to assess disease activity at baseline and week 12. Fecal calprotectin, which directly measures intestinal inflammation and is a useful clinical marker for predicting relapse, was measured at baseline and week 12. Microbial profiling in the stool samples was analyzed by 16S ribosomal RNA sequencing.

The primary objective of the study was to ascertain whether a Mediterranean diet has the potential to reduce disease activity as measured by the SCCAI score at week 12. A reduction of SCCAI above 1.5 was considered clinically significant. The secondary objective was to investigate possible changes in the fecal calprotectin concentration and the gut microbiome.


At week 12, the results of the Partial Mayo Score, which assesses disease activity, increased by 46% in patients with mild and moderate disease on the Canadian habitual diet compared to an increase of 33% in patients with mild disease on the Mediterranean diet.

The majority of participants in both groups had a fecal calprotectin concentration of less than 100 μg/g at baseline. At week 12, 87% of patients on the Mediterranean diet had a fecal calprotectin concentration below 100 μg/g compared to 25% of participants on the Canadian habitual diet. It is noteworthy that the concentration of fecal calprotectin remained unchanged in patients on the Mediterranean diet during the study; however, it increased in patients on the Canadian habitual diet after 12 weeks compared to the baseline concentration.

The Mediterranean diet significantly increased fecal sIgA levels, which are implicated in mucosal immunity by binding pathogenic bacteria and ultimately influencing the microbiota composition. In contrast, the Canadian habitual diet did not change the fecal sIgA concentration.

The findings also revealed that patients on the Mediterranean diet had higher levels of total fecal short-chain fatty acids, acetic acid, and butyric acid than the Canadian habitual diet group. Fecal short-chain fatty acids are produced by microbes and possess important immunomodulatory properties. Previous research has shown that patients with inflammatory bowel disease have lower levels of total fecal short-chain fatty acids and reduced abundance of total fecal short-chain fatty acid-producing bacteria than healthy controls.

The Mediterranean diet/ Canadian habitual diet and the gut microbiome



The Mediterranean diet reshaped the gut microbiome, triggering changes in the microbial species that play a protective role in colitis. Of the top 10 taxa most positively associated with the Mediterranean diet, 9/10 taxa belong to the phylum Firmicutes, class Clostridia, and mainly Clostridium subclusters IV (Ruminococcus spp., Flavonifractor spp), subcluster XIVa (Clostridium M, Blautia A), and Lactococcus spp. One taxon belongs to the phylum Bacteroidota, genus Alistipes. According to previous studies, some of these species have a protective role in rodent models of colitis or are involved in the degradation of compounds from food substrates that regulate host health (Clostridium boltae, Ruminococcus bromii, Blautia A spp., and Lactococcus lactis).

The genera negatively associated with the Mediterranean diet belong to opportunistic pathogens, such as Veillonella dispar, Veillonella obetsuensis, Prevotella copri, and Streptococcus australis.


This study has shown that the Mediterranean diet, compared to the habitual diet, induced changes in the gut microbiome, reduced fecal calprotectin concentrations, and elevated levels of fecal short-chain fatty acids. These outcomes are associated with maintenance of clinical remission in patients with quiescent ulcerative colitis.

The authors concluded that the Mediterranean diet is a healthy dietary pattern. It may be recommended to patients with remission of ulcerative colitis to prevent relapse, in addition to their standard medical therapy.

This article was published in the Journal of Crohn’s and Colitis.

Journal Reference

Haskey N. A Mediterranean Diet Pattern Improves Intestinal Inflammation Concomitant with Reshaping of the Bacteriome in Ulcerative Colitis: A Randomised Controlled Trial. Journal of Crohn’s and Colitis, 2023, XX, 1–10. Advance access publication 24 April 2023 (Open Access).


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