Fiber: Influential prebiotic for gut health

We’ve heard countless stories from our clients about how their doctors tell them diet doesn’t make a difference for their inflammatory bowel disease (IBD). But with recent scientific advances in our understanding of both IBD etiology and the role of the microbiome, it is becoming clear that this view is outdated: what we eat and what we feed our gut microbes plays a crucial role in healing and preventing flares. In this blog, we discuss why exactly fiber is so significant for people with IBD. At IBDCoach, we believe that reaching remission is based on three biological mechanisms: 

  1. Stopping inflammation 
  2. Rebalancing the microbiome 
  3. Repairing the intestinal barrier. 

Fiber addresses all of these.

What is fiber, and why do I need it?

The term “fiber”, in its broadest nutritional sense, refers to indigestible carbohydrates and lignins found intact in whole plants. There are various types of fiber, all with varying characteristics like solubility, fermentability, and even viscosity (we’ll cover more on viscosity in a future post). Each of these characteristics determines the biological function of the fiber critical for our health. 

  1. Soluble fiber absorbs water in the stomach and small intestine to form a gel that slows digestion. As a result, it can prevent erratic blood sugar spikes and keep you feeling full for longer. 
    • Examples of soluble fiber include pectins, gums, and inulin which are found in foods like citrus fruits, oats, legumes, and some vegetables. 
  2. Insoluble fiber (also referred to as roughage) does not break down in the small intestine, and instead draws in water to add bulk to stool to aid its passage through the large intestine. 
    • Examples of insoluble fiber include cellulose, hemicellulose, and lignin which are found in foods like leafy greens, seeds, whole grains, and vegetable skins. 

Beyond the benefits of stool formation and gut transit, the fermentability of fiber has powerful implications for our health. Our stomach enzymes do not digest fiber directly; instead, fiber in foods is passed along undigested to the colon where our bacteria is then able to metabolize it through fermentation, conferring beneficial effects for gut health.  For example, Bifidobacteria, a commensal bacteria in our colon, produces enzymes that break down a type of fiber called inulin (found in onions). Reports have shown a correlation between inulin consumption, Bifidobacteria activity, and a subsequent increase in the production of butyrate, an essential metabolite for gut health.(1) Since different fiber types have varying degrees of fermentability, they are not equally capable of stimulating metabolite production. Nonetheless, we are now learning that this fermentation of fiber is imperative for gut health.

How fermentation of fiber addresses IBD mechanisms

Butyrate, along with other short-chain fatty acids (SFCAs) such as acetate and propionate, are all byproducts of the fermentation of fiber in the gut. These metabolites serve several crucial functions in gut health including motility, communication with the mucosal immune system, and maintenance of the intestinal barrier by ensuring tight junction integrity.(2) Moreover, there is evidence that SCFAs mediate gut inflammation by regulating cytokines involved in the IBD inflammatory response.(3,4)

Additionally, consuming fiber has huge implications for our resident gut microbes themselves. Studies have associated a decrease in fiber intake with a reduction in bacterial diversity and dysbiosis, an altered microbial environment seen in people with GI disorders.(5,6) In fact, without fiber to feed on, bacteria in our gut can begin eating the protective mucus layer, causing more GI distress.(7) Conversely, research shows diets rich in fiber increase the beneficial bacteria in our gut, out-competing pathogenic bacteria.(8) Overall, by the means of fermentation, we see how fiber addresses all three mechanisms of IBD: the intestinal barrier, inflammation, and our microbiota.

Applying the evidence to our diet

Traditionally, people with IBD have been recommended to avoid all fiber. Now, we are seeing that train of thought may be more detrimental to gut health in the long run. Nonetheless, the texture of fiber is important to consider. During active flares, it is still encouraged to stay away from the “roughage” found in insoluble fiber as it can exacerbate symptoms.(9) In order to still feed your microbiota and prevent issues with texture, you can blend or purée soluble fiber to form a gel-like substance. Because tolerances to fiber-rich foods vary, it’s usually suggested to introduce fiber consumption slowly as everyone’s digestive system responds uniquely. 

Barbara Olendski, RD associate professor at the University Massachusetts has implemented this new evidence to create the IBD Anti-Inflammatory Diet (IBD-AID) which prioritizes foods that feed beneficial bacteria and avoids foods thought to have adverse effects on the microbiome such as gluten, corn, lactose, etc. She believes adjustments to the texture of soluble fiber for different disease states is the best way to feed the gut microbiota and avoid further tissue damage until inflammation subsides. For some of her patients, she suggests the addition of digestive enzymes to aid in the digestion of fiber. Ultimately, because IBD-AID targets each IBD mechanism by the use of fiber, it has shown in practice to help many people achieve remission.


In summary, research has demonstrated that certain fibers can fortify the gut’s intestinal barrier, immune function, and microbiota composition. Although there is not enough conclusive evidence to create an official fiber recommendation for people with IBD, the potential of utilizing fiber as an anti-inflammatory therapeutic is quite promising. Of course, some of these beneficial effects may also result from the other nutrients and minerals required for health that are often found in fiber-rich fruits and vegetables. Due to variables like genetics, our unique microbiome, and individual disease state, there is no “one size fits all” when it comes to nutrition. As always, be sure to speak with your medical team before making any dietary changes, especially for individuals with strictures and intestinal obstruction. 

For more information on how to appropriately introduce fiber into your diet, check out the University of Massachusetts website on IBD-AID. Andrew also has some great recipes on his food blog containing soluble fiber (like his his blueberry, banana, avocado, cacao smoothie!).


  1. Rossi, M. et al. Fermentation of Fructooligosaccharides and Inulin by Bifidobacteria: a Comparative Study of Pure and Fecal Cultures. Appl. Environ. Microbiol. 71, 6150–6158 (2005).
  2. Parada Venegas, D. et al. Short Chain Fatty Acids (SCFAs)-Mediated Gut Epithelial and Immune Regulation and Its Relevance for Inflammatory Bowel Diseases. Front. Immunol. 10, 277 (2019).
  3. Cr, C. et al. Differential effects of short-chain fatty acids on proliferation and production of pro- and anti-inflammatory cytokines by cultured lymphocytes. Life Sci. 73, 1683–1690 (2003).
  4. Asarat, M., Apostolopoulos, V., Vasiljevic, T. & Donkor, O. Short-Chain Fatty Acids Regulate Cytokines and Th17/Treg Cells in Human Peripheral Blood Mononuclear Cells in vitro. Immunol. Invest. 45, 205–222 (2016).
  5. Holscher, H. D. Dietary fiber and prebiotics and the gastrointestinal microbiota. Gut Microbes 8, 172–184 (2017).
  6. A fiber-deprived diet disturbs the fine-scale spatial architecture of the murine colon microbiome | Nature Communications.
  7. Sonnenburg, E. D. & Sonnenburg, J. L. Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates. Cell Metab. 20, 779–786 (2014).
  8. Makki, K., Deehan, E. C., Walter, J. & Bäckhed, F. The Impact of Dietary Fiber on Gut Microbiota in Host Health and Disease. Cell Host Microbe 23, 705–715 (2018).
  9.  Levine, A. et al. Dietary Guidance From the International Organization for the Study of Inflammatory Bowel Diseases. Clin. Gastroenterol. Hepatol. Off. Clin. Pract. J. Am. Gastroenterol. Assoc. 18, 1381–1392 (2020).

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