Inflammatory bowel diseases (IBD), which include ulcerative colitis (UC) and Crohn’s disease (CD), are gastrointestinal disorders in which a burst of inflammation plays a central role. IBD patients suffer from diarrhea, abdominal pain, bloody stools, weight loss, fever, and fatigue. There are two phases of the disease: a remission phase with no symptoms, and an active phase, also called “flare-up,” during which patients experience symptoms due to increased inflammation. There is no cure for IBD, and the goal is to continue being in remission for as long as possible using diet and anti-inflammatory drugs.
Dietary fibers found in fruits, vegetables, cereals and starchy foods, have been shown to stimulate the production of the SCFAs by the gut bacteria. One of the most studied fibers with the capacity to stimulate the growth of gut beneficial bacteria are β-fructans (fructooligosaccharides and inulin) which are long molecules of carbohydrates composed of several units of fructose. Bacteria that possess the enzymes that are capable of breaking down specific linkages in complex β-fructans into simple units of sugar will produce SCFAs that regulate the immune system and stimulate colonic repair. However, the role of dietary fibers in patients with IBD who are afraid of suffering flare-ups, has been largely ignored.
Altogether, are dietary fibers increasing, promoting, or decreasing inflammation symptoms in individuals with IBD? This is a question that Dr Armstrong et al. aimed to answer.
The authors found that unfermented dietary β-fructans stimulate inflammation and leading to gut barrier changes in a subset of biopsy samples from pediatric patients with IBD. Indeed, β-fructans present in the gastrointestinal tract can bind to human cells involved in the immune system such as monocytes and macrophages, thus stimulating an inflammatory response.
In a second part, Dr Armstrong et al. show that the fermentation of β-fructans increases the releases of the beneficial SCFAs and thus reduces inflammation. The gut microbiota of IBD patients in flare-up, on the other hand, is unable to adequately ferment fibers and thus produce less SCFAs. Not only do unfermented β-fructans stimulate inflammatory responses in biopsy samples, but IBD patients in flare-up lack SCFAs capable of reducing inflammation. The team of researchers also found that IBD patients with a high production of inflammatory compounds in the gut consumed less fructans-type fiber, which suggests that patients unknowingly avoid such fibers to improve symptoms.
Finally, the authors confirmed the pro-inflammatory response of β-fructans in a small group of adult patients with UC. For most of the UC patients in remission, the supplementation of β-fructans (15 g/d over 6 months) resulted in a reduced risk of flare-up. However, in a subset of UC patients, β-fructans increased inflammation and did not protect against flare-ups. These findings show that even the same type of fiber can lead to an improvement or worsening of flares depending on the gut microbiota, the disease course and type of fiber, which researchers want to explore in future studies.
In conclusion, while β-fructans are beneficial in healthy individuals, this type of dietary fiber may have positive or detrimental effects depending on individual gut microbiota and disease course (remission or active disease). These findings underline the need for personalized nutritional therapy over a one-size-fits-all diet in individuals with IBS.
References:
Armstrong HK, Bording-Jorgensen M, Santer DM, et al. Unfermented β-fructan Fibers Fuel Inflammation in Select Inflammatory Bowel Disease Patients. Gastroenterology. 2023;164(2):228-240. doi:10.1053/j.gastro.2022.09.034
Shin A, Kashyap PC. Promote or Prevent? Gut Microbial Function and Immune Status May Determine the Effect of Fiber in Inflammatory Bowel Disease. Gastroenterology. 2023 Feb; 164(2):182-184. doi:10.1053/j.gastro.2022.11.022
