An email from a friend with ulcerative colitis prompted me to write this post. She referred to my most recent publication:
- Brotherton CS, Martin CA, Long MD, Kappelman MD, Sandler RS. Avoidance of Fiber Is Associated With Greater Risk of Crohn’s Disease Flare in a 6-Month Period. Clin Gastroenterol Hepatol. 2015 Dec 31. pii: S1542-3565(15)01713-9. doi: 10.1016/j.cgh.2015.12.029. [Epub ahead of print]
She shared her guess as to why we found no association between ulcerative colitis flares and fiber.
My friend’s email triggered me to share here my hypothesis for why our study only found a fiber association in Crohn’s disease, not in ulcerative colitis.
My short explanation…
I believe that for fiber to help people with IBD, the fiber type must match the location of inflammation. Soluble fibers that ferment early in the digestive system produce beneficial short-chain fatty acids that may never reach the distal inflammation of ulcerative colitis. Insoluble fibers that are slower to digest deliver the healing properties of short-chain fatty acids to the more distal digestive system where ulcerative colitis inflammation flares[1,2].
I believe we saw a fiber association in Crohn’s disease and didn’t see a fiber association in ulcerative colitis because there is currently a strong bias against insoluble fiber for IBD. Insoluble fiber (wheat bran) shifts fermentation distally [1,2], delivering short-chain fatty acids further down the digestive tract than the point at which early-fermenting soluble fibers deliver benefits. Because inflammation in ulcerative colitis occurs more distally than inflammation in Crohn’s disease, the bias against insoluble fiber probably hurts patients with ulcerative colitis the most.
A little about ulcerative colitis:
In ulcerative colitis…
- patients suffer from symptoms similar to Crohn’s disease: chronic abdominal pain, chronic diarrhea, and chronic rectal bleeding
- patients often avoid fiber for the same reasons as people with Crohn’s disease. (See Five Reasons Fiber SEEMS Bad for IBD by clicking HERE.)
- the pathophysiology of gastrointestinal symptoms overlap with the pathophysiology of Crohn’s disease symptoms
Therefore, it is reasonable that people ask the following question…
Is the effect of fiber the same in ulerative colitis as in Crohn’s disease?
The answer is FAR from simple.
In the above study, we found that Crohn’s disease patients in the highest 25% of fiber intake were ~40% less likely to flare in 6 months. In the highest 10% of fiber intake, Crohn’s patients were ~60% less likely to flare. Crohn’s disease patients who didn’t avoid fiber were ~40% less likely to flare than patients who did avoid fiber.
We didn’t find similar associations in ulcerative colitis… does it mean fiber can’t help people with ulcerative colitis?
NOT NECESSARILY. Diet research is complex. All research studies have limitations… design problems that prevent full discovery of the answers to questions researchers want to investigate. Diet research is especially hard to design — drug studies are easier — one group gets a real drug and the other group gets a placebo. Diet research is different…
The foods people eat are infinitely variable and hard to control in research.
One of the limitations in our study is that we have no way of knowing the specific fibers participants were eating. In particular, we don’t know if the fibers participants were eating were fibers that ferment someplace other than the specific location in which each participant’s inflammation existed. Gathering and analyzing such detailed information would be incredibly informative, but it is not practical to do so at the present state of the science.
To better understand my hypothesis…
First, consider the location of inflammation in Crohn’s disease vs. ulcerative colitis.
Crohn’s disease inflammation occurs anywhere in the digestive tract, from mouth to anus (mouth, throat, esophagus, stomach, small intestine, colon). The most common site is the small intestine.
Ulcerative colitis inflammation only occurs in the colon.
Next, consider how location of inflammation relates to different fiber types.
The types of fibers eaten make a huge difference — because different fibers deliver benefits to different parts of the gut!
For a food component to have an impact on inflammation in ulcerative colitis, the component has to survive the trip through the whole digestive system — the mouth, throat, esophagus, stomach, and small intestine — before reaching the point of need, which is the colon. Insoluble fiber, specifically wheat bran, does just that. By reaching the colon before fermenting, insoluble fiber/wheat bran helps deliver the healing properties of short-chain fatty acids right to the site of inflammation. (For a little more about short-chain fatty acids, see the webpages entitled, Fiber Feeds Good Gut Bacteria by clicking HERE and Good Bacteria Heal the Gut by clicking HERE.)
Insoluble fiber/wheat bran shifts the site of bacterial fermentation to a later location in the digestive system [1,2]. In contrast, without wheat bran, soluble fibers ferment EARLIER in the digestive system [1,2]. Early fermentation means that the benefits of short-chain fatty acids are more likely to be absorbed in locations affected by Crohn’s disease, but never reach the distal gut affected by ulcerative colitis.
Another benefit of insoluble fiber/wheat bran reaching the distal colon intact is the capacity to soak up and hold excess water  present in the DISTAL digestive system of ulcerative colitis patients during a flare. Excess water remains in the lumen of the intestine when the intestinal lining is inflamed and swollen and fails to absorb water normally. Fiber that soaks up and holds excess water slows the rush of intestinal contents , producing soft, comfortably-passed stool.
Finally, consider what IBD patients are being told about insoluble fiber.
There is good reason to assume that IBD patients fail to eat insoluble fiber.
Take a moment to Google the terms “insoluble fiber” and “ulcerative colitis”
Did you see it? Did you see why I think people with ulcerative colitis are purposely avoiding the very fiber type they need most? I will refrain from throwing anyone under the bus, but there is a lot of misinformation out there on the internet — authoritative-sounding statements about insoluble fiber that are not referenced with any scientific research studies. In other words, IBD patients are being told over and over again to avoid insoluble fiber, with no reference to research that supports the recommendation.
Little by little, IBD care providers are understanding the benefits of soluble fiber and SLOWLY starting to gain a little appreciation for the need for soluble fiber in IBD. However, insoluble fiber is still almost unanimously maligned. This attitude toward fiber causes me to get up every morning and do everything I can to educate anyone who cares about gut health and is willing to listen.
If you’ve read the pages of my website, you already know that fewer than 3% of Americans eat the recommended amounts of total fiber [5,6]. Now, considering the repeated warnings against insoluble fiber for IBD, isn’t it reasonable to assume that IBD patients are failing to eat much insoluble fiber? The fiber our IBD participants DID eat was probably soluble — doesn’t it make sense that a lack of insoluble fiber in our study might have kept us from seeing a benefit from fiber in ulcerative colitis?
You can read about how our published article has been received by clicking HERE.
Also, a short YouTube Video Abstract for the article will be uploaded by the American Gastroenterological Association soon, and I will add a link to the video here when the video is posted.
In the future, I will add a review of research studies that have shown some favorable effects from research related to the question of fiber and ulcerative colitis.
- Pryde SE, Duncan SH, Hold GL, et al. The microbiology of butyrate formation in the human colon. FEMS Microbiol Lett 2002;217:133-139. Read the full article by clicking HERE.
- Muir JG, Yeow EGW, Keogh J, et al. Combining wheat bran with resistant starch has more beneficial effects on fecal indexes than does wheat bran alone. American Journal of Clinical Nutrition 2004;79:1020. Read the full article by clicking HERE.
- Fine KD, Schiller LR. AGA technical review on the evaluation and management of chronic diarrhea. Gastroenterology 1999;116:1464-1486. Read the full article by clicking HERE.
- Harvey RF, Pomare EW, Heaton KW. Effects of increased dietary fibre on intestinal transit. The Lancet 1973;301:1278-1280. Read the abstract by clicking HERE.
- Clemens R, Kranz S, Mobley AR, et al. Filling America’s fiber intake gap: summary of a roundtable to probe realistic solutions with a focus on grain-based foods. J Nutr 2012;142:1390S-1401S. Read the full article by clicking HERE.
- Agricultural Research Service, U. S. Department of Agriculture. Dietary fiber (g): Usual intakes from food and water, 2003-2006, compared to adequate intakes. What we eat in America, NHANES 2003-2006. Volume 2013, 2010.