One first needs to understand what fiber is…
Dietary fiber is described as ‘indigestible,’ because dietary fiber is the part of food that cannot be digested by human enzymes. Many people believe that being indigestible is the same as being irritating or inflammatory. However, scientific research has NOT shown dietary fiber to be irritating or inflammatory – just indigestible, which is a good thing! Being indigestible means fiber reaches the distal intestines where it can do good things. Future pages on this website will describe the anti-inflammatory mechanisms of dietary fiber that have been seen in scientific research.
5 Reasons People Think Dietary Fiber is ‘Bad’ for IBD
1. People have always said dietary fiber is bad for IBD.
In the 1800s, polluted water and infected milk often caused bouts of diarrhea and gut inflammation.1 These were cases of acute infectious diarrhea. In those days, avoiding food (especially fiber) helped to decrease the diarrhea. After the body’s immune system succeeded in stopping the infection, the person could return to a normal diet and there was no long-lasting effect.
About a hundred years ago, after people started eating industrialized foods, a new type of diarrhea and bowel inflammation emerged: a chronic disease called inflammatory bowel disease (IBD). The dietary advice for the new disease remained the same as for the old disease: avoid dietary fiber. Unfortunately, the problem in IBD is an immune response that doesn’t turn itself off… a very different problem from an acute infection caused by polluted water or infected milk.
Medical books, nursing books, and dietetics books repeated a low fiber message for IBD since at least the 1920s.2 However, in a deep dive search, I could find no scientific evidence supporting a low fiber diet for improved gastrointestinal health for people with IBD. Still today, prestigious medical websites and patient-generated websites stress a low fiber message for IBD without citing any scientific evidence of effectiveness.
If you repeat something long enough, people believe it is true…
2. During a flare, eating fiber in non-therapeutic doses increases the amount of liquid stool passed (diarrhea).
During a flare of IBD, the wall of the intestine becomes swollen – water is not absorbed normally. The extra water in the intestine rushes through the system and cannot be controlled. Whatever is in the intestine comes through as diarrhea! During a flare, individuals are correct when they say, “Everything I eat runs right through me.”
Non-fiber parts of their food are digested by human enzymes early in the digestive system and never reach the distal intestine. In contrast, the fiber in their food is not digested and reaches the distal intestine. That means that when a non-therapeutic level of fiber is eaten during a flare, more matter is passed as diarrhea. It makes it easy to think, “Fiber makes me worse.”
However, there is no scientific evidence that an increase in diarrhea matter equals an increase in gut inflammation. I can’t wait to write about what it means to me to eat “a therapeutic level” of dietary fiber!
3. An increase in fiber temporarily increases intestinal gas.
Dietary fibers are complex carbohydrates that can only be broken down by friendly bacteria in the gut. Dietary fiber is the food source for friendly bacteria. More fiber leads to stronger and healthier colonies of friendly bacteria in the gut.
After increasing fiber intake, it takes time for the colonies of friendly bacteria to catch up with the increased food supply. During that time, there can be an increase in gas and 
bloating. Research has shown that it takes about 2 weeks of consistent use of increased fiber for the gas to go away. After that period of time, people sometimes find that there is less gas than there was before fiber was increased.3
Unfortunately, many people are unaware that the gas is temporary and the gas affects their perception of well-being. They try a little fiber and conclude, “My gut doesn’t like fiber.”
I can’t wait to write about the good things that happen when fiber is digested by friendly bacteria! The rest of the story is coming in future pages of my website!
4. A person with a stricture is a special case that requires strong caution regarding dietary fiber.
It is common for a person with Crohn’s disease to develop a stricture, which is a narrowed portion of bowel. Strictures complicate the topic of dietary fiber. Individuals with strictures need to understand that some fibrous foods can be dangerous or even life-threatening. Specifically, the hard fiber in raw foods like carrots and broccoli deserve extreme caution.
For example, imagine what can happen if a raw carrot is poorly chewed:
When a chunk of raw carrot reaches a stricture, it can easily block the flow of intestinal matter. This situation is a true medical emergency. The individual may require surgery to resolve the blockage.
With other types of fiber, such as wheat bran cereal, the fiber is able to soak up excess water4 and form a soft, malleable stool. In contrast to a carrot, a soft stool is better able to squeeze through narrow portions of bowel. Still, I have known even a soft stool to cause intense discomfort when it first squeezes through a stricture.
I have known more than one person with a history of strictures to start with a teaspoon of bran per day rather than a full serving. They then increased the amount by a teaspoon per week as tolerated. This way they gradually re-accustomed their bowels to the passage of formed stool.
Any person with Crohn’s disease or ulcerative colitis should always consult with his or her health care provider before making diet changes.
- Bauer WW. “Grandma is not always wrong”. Potions, Remedies and Old Wives’ Tales. Garden City, NY: Doubleday, 1969:173-197.
- Cooper LF, Barber EM, Mitchell HS. Diet in Diseases of the Intestines. Nutrition in Health and Disease. Philadelphia, PA: J.B. Lippincott, 1928:294-305.
- Grabitske HA, Slavin JL. Gastrointestinal effects of low-digestible carbohydrates. Critical reviews in food science and nutrition 2009;49:327-360.
- Taghipoor M, Barles G, Georgelin C, et al. Digestion Modelling in the Small Intestine: Impact of Dietary Fibre. Math Biosci 2014;258:101-112.