By Colleen D. Webb, MS, RDN, CLT

One of the most common conversations I have with patients with inflammatory bowel disease (IBD) is about the low-fiber diet. Even if you have limited nutrition knowledge, you probably know that fiber is good for human health. So, it surprises folks with Crohn’s or ulcerative colitis when a healthcare provider tells them to follow a low-fiber diet for their disease. It’s a catch-22. Fiber is an important part of a healthy diet, but too much fiber can upset an irritated or inflamed gut.

Fortunately, most people with IBD need not avoid all high-fiber foods on a low-fiber or low-residue diet. There are ways that you can reap fiber’s health benefits without irritating your gut.

We’ll show you how you can eat a nutritious, anti-inflammatory, minimally processed, low-fiber diet.

Keep reading to learn more about dietary fiber, why we need it, and how to eat it with IBD.

What is Dietary Fiber?

Dietary fibers are non-digestible carbohydrates found in plants. Humans can’t break down fiber so it travels throughout the gastrointestinal tract and exits more or less the same way it came in. That’s why we see corn in the toilet.

All fibers are not the same. There are different types with varying characteristics. Health organizations have tried to define them, but the definitions are imperfect and inconsistent.

More often than not, you’ll hear fiber described as “insoluble” or “soluble.”

Soluble fiber is more fully fermented in the large intestine and has a higher gel-forming capacity than insoluble fibers. Humans can’t digest fiber, but microbes can. When a fiber is fermentable, that means bacteria can metabolize it in the colon. These are prebiotic fibers. When a fiber has a higher gel-forming capacity, that means it’s viscous. Soluble fiber is more fermentable and viscous than insoluble fiber, although certain insoluble fibers are fermentable.

I like to refer to insoluble fiber as “roughage” because of its coarse nature. Roughage has a mechanically irritating effect on the large intestine, triggering water and mucus secretion.

Think of an apple. The inside of the apple is the soluble fiber, whereas the apple skin is the roughage. This illustration applies to most fruits and vegetables. Their insides are soft and soluble whereas the skins and stalks are roughage.

Rarely do I use the term “fiber” with my patients. Instead, I talk to them about roughage. A low-roughage diet can help manage symptoms and provide the gut with some rest. More on this later.

Why Dietary Fiber is Good For Us

The best diets for human health are high in fiber. Dietary fiber is best known for its ability to lower blood cholesterol, regulate blood sugar, promote fullness, improve bowel regularity, reduce risk of certain cancers, and protect against disorders of the large intestine (colonic disorders).

Even though humans lack the tools to break down fiber, our colonic microbes (mostly bacteria) ferment fiber to make beneficial by-products. One of these by-products is butyrate.

Butyrate is a short-chain fatty acid that helps to reduce inflammation and strengthen the intestinal barrier. A butyrate deficiency can cause the gut barrier to breakdown leading to increased intestinal permeability or “leaky gut.” Research has shown that increased intestinal permeability precedes flares in people with IBD.

When microbes don’t have fiber to eat, they feed on the protective mucus lining of the gut, eroding it. This puts us at risk for intestinal infections and inflammation.

Understandably, lots of patients who see me for nutrition counseling express frustration and concern over having to follow a low-fiber diet. Most healthcare providers tell their patients to eat high-fiber diets to help them live longer and better lives!

A 2019 meta-analysis of 40+ years worth of research concluded that humans should eat at least 25-29 grams of fiber per day to prevent chronic disease and early death.

Why are People with Crohn’s and Ulcerative Colitis Told to Avoid High-Fiber Foods?

If dietary fiber is so good for us, why is a low-fiber diet recommended for people with Crohn’s and ulcerative colitis?

1. Certain high-fiber foods can worsen gastrointestinal symptoms, including gas, bloating, abdominal cramping, diarrhea and constipation.

2. Foods high in roughage can irritate the bowel thanks to their coarse nature. Imagine rubbing sandpaper on an open wound. Ouch! Roughage includes thick skins and stalks of fruits and vegetables, whole nuts and seeds, and popcorn.

3. Roughage can lead to bowel obstructions in at-risk individuals. People most likely to obstruct include those with a prior history of abdominal surgery and/or stricturing Crohn’s disease.

Common Questions About Fiber and IBD

Here are some of the most popular questions I get about fiber and IBD:

Do I have to follow a low-fiber diet forever?

For most people, the answer is “no.” Having IBD does not mean you have to avoid fresh fruits, vegetables and other high-fiber foods forever. Limiting or avoiding roughage during flares is important because high-roughage foods make the gut work harder. Rest is an important step in the healing process.

Important: there is zero evidence that fiber causes IBD flares. But, there is evidence that high-fiber diets might help protect against flares. That’s why it’s important to work with a GI-dietitian to help add back fiber to your diet when the time is right.

Those at risk of obstructing might need to follow a low-roughage diet forever.

Does fiber cause flares?

We have no reason to believe fiber causes flares. See question 1.

Do cooked vegetables have any health benefits?

Absolutely! Some vegetables are healthier cooked whereas others are better raw. Cooking vegetables breaks down the rough cellulose fiber, which is the major component of the cell walls of plants. Breaking these down makes more of the plants’ nutrients available to us. Besides cellulose, plants have other ingredients that can sometimes interfere with our absorption of nutrients. Cooking can break these down, too.

Now that I’m feeling better, how can I add vegetables back to my diet?

Here are some tips for reintroducing vegetables:

1. Add one vegetable at a time. Adding more than one food per sitting increases your risk of feeling unwell and will make it more difficult to determine the offending food.
2. Start with a small amount. One-quarter cup is a good starting point for vegetables.
3. If the vegetable has a peel then peel it. If it has a stalk then remove it (e.g. broccoli, asparagus). If it can be cooked then cook it. Cooked and peeled vegetables are easier for the gut to break down.
4. Chew your food very well and eat slowly. This applies to all foods, all the time.
5. Choose a relaxed environment to reintroduce foods. Stressful environments can hinder your tolerance.
6. Challenge foods more than once. Your tolerance to foods with and without fiber will change as your disease changes. Foods that upset your gut today might be fine in the future. For example, Scott had to avoid broccoli for a few years because it lead to bloating. Now it’s a staple in his diet.

Not sure where to start? Lots of people with IBD fare well with root vegetables, like carrots, parsnips, and turnips, because they can be peeled and mashed. Others prefer peeled zucchini, summer squash and seeded cucumbers.

How can I eat healthy on a low-fiber diet?

Start thinking in terms of “roughage” versus fiber. Think of the texture of the food when you swallow it. If the food is soft or pureed, then it’s low roughage. If it’s tough and coarse, then it’s high roughage.

Some high-fiber foods are low roughage. For example, an avocado has a lot of fiber, but it’s not rough. Usually people on low-fiber diets eat avocado without an issue. Same idea with nut butters. Whole nuts, such as almonds, are high roughage, but creamy almond butter is low roughage.*

Examples of low-roughage foods that have fiber:

• Fruit without tough skins and seeds: Banana, avocado, cantaloupe, peeled apple, and peeled and seedless cucumber
• Well-cooked vegetables without tough skins, seeds or stalks: Peeled and cooked winter squash, carrots, parsnips, potatoes without skin, sweet potatoes without skin, yams without skin, turnips
• Soups
• Smoothies (you don’t need to cook fruits or vegetables before placing in high-powered blender)
• Creamy nut and seed butters: almond butter, peanut butter, tahini
• Hummus

*Foods can upset people for reasons other than fiber. Work with your GI dietitian to identify safe foods.

Examples of Healthy Meals on a Low-Fiber Diet

Fortunately, you can eat well on a low-fiber diet. Here are some favorite low-fiber, nutritious meal ideas:

• Yogurt Parfait: Mix a plain Greek yogurt or dairy-free yogurt with all-natural almond butter, sliced banana and melon
• Fruit & Vegetable Smoothie: So many options! See our IBD Smoothie Guide
• Vegetable Omelet: Scramble eggs with well-cooked vegetables
• Pasta: Combine regular or gluten-free pasta with a basil or basil-spinach pesto
• Roast chicken with baked sweet potato fries
• Baked white fish with a baked potato and roasted butternut squash
• Avocado Toast: I like traditional sourdough bread for my patients
• Soups! We love carrot, butternut squash, ginger soup

Key Takeaways

OK, let’s review. Here are some key points to remember about fiber and IBD:

• Dietary fiber is important for human health.
• Without dietary fiber, our gut microbes don’t have the food they need to protect our gut lining and reduce inflammation.
• You need not avoid all high-fiber foods on a low-fiber diet. Think in terms of “roughage” versus fiber.
• Living with IBD does not mean avoiding fiber for the rest of your life.
• Peeling, blending, and/or cooking high-fiber foods helps to break down the hard-to-digest roughage.
• Work with an IBD-focused registered dietitian to help you create a low-roughage, anti-inflammatory diet to help manage your Crohn’s or ulcerative colitis.

Below we invite you to share your favorite low-roughage meal ideas!