Intake of dietary fiber reduces risk of disease flares in patients with Crohn’s disease, but not ulcerative colitis, researchers report in the August issue of Clinical Gastroenterology and Hepatology. Recommendations to limit dietary fiber should therefore be re-evaluated.
Inflammatory bowel diseases (IBD) have been associated with an abnormal mucosal immune response to commensal gut microbes in genetically susceptible individuals. Diet, particularly dietary fiber, can affect the gastrointestinal microbiota and might affect the course of disease development. Although fiber might benefit patients with IBD, through generation of short-chain fatty acids such as butyrate, patients are often instructed to limit their fiber consumption.
Guidelines have recommended that because of the potential risk of a mechanical obstruction, patients with Crohn’s disease and strictures should avoid high fiber diets. Unfortunately, this recommendation has led to confusion from some patients and physicians who perceive that fiber should be avoided in all patients with IBD.
Using the Crohn’s and Colitis Foundation of America’s Partners database, Carol S. Brotherton et al studied the association between fiber exposure and disease flares in patients with Crohn’s disease (n = 1130) or ulcerative colitis (n = 489). Brotherton et al enrolled patients whose disease activity index was defined as remission at baseline and followed each patient for a flare (increased disease activity index, hospitalization, or surgery) within 6 months of evaluating their fiber consumption.
The authors found that although fiber intake in the overall study population was similar to that of the U.S. population (about 17 g/day), subjects with longer duration of disease, past history of surgery, and past IBD hospitalization ate less fiber. Few participants consumed ultra-high-fiber bran cereal, and 30% of participants avoided dietary fiber altogether.
Patients with Crohn’s disease whose median intake of fiber was 23.7 g/day were ∼40% less likely to have a flare than patients whose median consumption was 10.4 g fiber/day.
Interestingly, patients with Crohn’s disease who reported that they purposely avoided high fiber foods (30%) had a higher likelihood of flaring than non-avoiders. In contrast, fiber consumption made no difference in patients with ulcerative colitis.
Researchers have proposed since at least the 1970s that the lack of dietary fiber in industrialized diets is an important factor in the increasing incidence of IBD. Scientists have been studying the effects of increasing fiber metabolites (short-chain fatty acids) and fiber supplements, but the findings from the current study support the idea that the fiber content of everyday foods can affect IBD progression.
The authors are not sure why some patients with Crohn’s disease were avoiding fiber—it could be because of physician instructions or participant preference. Participants with stricturing disease might have avoided fiber because they developed symptoms such as bloating when they ate certain fibrous foods, or to prevent obstructive symptoms. It could be that subjects who underwent surgery continued with a low-fiber diet after it was warranted.
In an editorial that accompanies the article, Gilaad G. Kaplan writes that the findings of Brotherton et al indicate that in the absence of a known fibrostenotic stricture with obstructive symptoms, a high fiber diet is likely safe and benefits patients with IBD. He says that although the findings of Brotherton et al contradict those from a systematic review of randomized controlled trials (in 12 trials of patients with Crohn’s disease, fiber did not affect disease flare to remission or remission to flare), most of these trials had small sample sizes, and there was significant heterogeneity among studies.
Brotherton et al state that prospective studies are needed to determine the benefits of fiber-containing foods in diets of individuals with different types of IBD. Although it is unlikely that a single diet will be found to benefit all patients with IBD, it would be remarkable progress if specific dietary features were found to benefit some or most patients.