Mastering a High-Fiber Diet for IBS: Foods to Eat & Avoid

Have you been recommended to follow a high-fiber diet for irritable bowel syndrome (IBS)? While it may seem pretty straightforward, getting more fiber is not so simple with IBS. Certain high-fiber foods and supplements can trigger IBS symptoms.

Read on for what you need to know about increasing fiber for the management of IBS. We’ll cover the different types of fiber and help you figure out what foods to eat and avoid.

Understanding IBS and the Role of Fiber

Irritable bowel syndrome is a condition that impacts the digestive tract. IBS causes a range of symptoms, including cramping, abdominal pain, bloating, and gas. It’s often classified by subtype based on symptoms.

IBS Subtypes:

• IBS-D: irritable bowel syndrome, diarrhea dominant

• IBS-C: irritable bowel syndrome, constipation dominant

• IBS-M: irritable bowel syndrome mixed (both constipation and diarrhea)

Breaking IBS into subtypes helps determine which tests or treatments to prioritize. 

IBS is considered a chronic condition, meaning therapy focuses on symptom management. One IBS management tool is diet. Nutrition recommendations for IBS may include eating more fiber or trialing a low FODMAP diet.

Fiber is a carbohydrate that cannot be broken down by the body. There are two types of fiber: insoluble and soluble. Insoluble fiber passes through the digestive tract unchanged, whereas soluble fiber is fermented by bacteria in the microbiome. 

How Fiber Affects IBS Symptoms

While the causes of IBS are not yet fully understood, there are a few potential symptom drivers that fiber may help address.

Some cases of IBS can be caused by altered gut motility which means that food moves either too fast or too slow through the digestive tract. Slow motility could play a role in IBS-C, whereas fast motility could play a role in IBS-D. 

Fiber is a helpful tool with a dual benefit for gut motility. Dietary fiber adds bulk to stool, making bowel movements easier and more comfortable for individuals with IBS-C. For those with IBS-D, fiber helps solidify stool  by soaking up water in the digestive tract.

Another potential cause of IBS symptoms is an imbalance in the gut microbiome. This would either be from too much bacteria in the large intestine or an improper balance of overall microbes. Research shows that fiber feeds beneficial bacteria, promoting a balanced microbiome and helping with IBS symptoms.

Soluble vs. Insoluble Fiber: Which Is Better for IBS?

Research suggests that soluble fiber is more beneficial for IBS symptom management than insoluble fiber. In some cases, insoluble fiber may trigger symptoms. Scientists have yet to fully understand why this is, but a potential explanation is that insoluble fiber bulks up the stool which can therefore negatively impact gut motility for those with IBS.

Foods to Eat on a High-Fiber Diet for IBS

High fiber foods such as whole grains, nuts, and beans typically contain a combination of both soluble and insoluble fiber. 

Soluble Fiber Sources

A variety of foods are good sources of soluble fiber. Some examples include the following:

• Fruits: apples, berries, avocado

• Vegetables: carrots, green beans, sweet potato

• Whole Grains: barley, brown rice, oats

• Legumes: lentils, beans, peas

• Nuts and Seeds: chia seeds, flaxseeds, almonds

However, many high-fiber foods are also high in FODMAPs. FODMAPs are types of carbohydrates that are not well absorbed by the gut. FODMAP-rich foods can trigger symptoms in people with IBS. 

Incorporating Low FODMAP, Fiber-Rich Foods

The low FODMAP diet is a temporary elimination diet to help reduce the symptoms of IBS. The first phase of the diet is a strict elimination phase to reduce the amount of fermentable carbohydrates in the diet. These include foods high in fructose, lactose, and certain types of sugar alcohols, called polyols. Fermentable carbohydrates are thought to be difficult to digest for many people with IBS. This is because they are not broken down until they reach the large intestine where they serve as food for gut bacteria. These microbes can produce certain gases that can be a trigger for IBS symptoms.

After a period of elimination, high FODMAP foods are then added back to the diet during planned food challenges to help determine an individual’s IBS symptom triggers.

It can be challenging to consume enough fiber during the elimination period because many fiber-rich foods are high in FODMAPs. Still, some low FODMAP, fiber-rich foods exist. The following are low FODMAP fiber sources:

Low FODMAP Serving Size

Grams of Fiber:

• Popcorn, commercial

  • 3.5 cups, 8 grams of fiber

• Chia seeds, dried

  • 2 tablespoons, 8 grams of fiber

• Buckwheat groats, cooked

  • ¾ cup, 7 grams of fiber

• Kiwi, green, peeled

  • 2 small, 6 grams of fiber

• Oats, rolled, uncooked

  • ½ cup, 5 grams of fiber

• Flaxseed

  • 1 tablespoon, 4 grams of fiber

• Tahini

  • 2 tablespoons, 4 grams of fiber

• Broccoli

  • ¾ cup, 3 grams of fiber

• Spinach, raw, chopped

  • 1.5 cup, 3 grams of fiber

• Raspberry, raw

  • 30 berries, 3 grams of fiber

Getting enough fiber during the elimination phase requires planning and careful food selection. It is helpful to work with a registered dietitian during this time.

Foods to Avoid on a High-Fiber Diet for IBS

Although fiber is essential for gut health, some fiber sources can trigger IBS symptoms. 

Insoluble Fiber Triggers

Insoluble fiber may actually trigger IBS symptoms. Research shows that corn and wheat bran, which are both sources of insoluble fiber, could worsen IBS symptoms.

Although insoluble fiber may contribute to IBS symptoms, you may not need to avoid all insoluble fiber sources. 

High FODMAP, High Fiber Foods That May Aggravate IBS

Many high FODMAP foods are also good sources of fiber. However, these foods are often avoided on a low FODMAP diet because they can worsen IBS symptoms.Examples of high FODMAP, high fiber foods include:

• Artichokes, asparagus, cauliflower

• Apples, cherries, mango

• Whole grain products made from wheat, barley, or rye

• Cashews, pistachios

Portion sizes matter for high FODMAP foods. Some high FODMAP foods may be enjoyed at certain portion sizes, even during the elimination phase. It’s important to note that the low FODMAP diet should only be done under the guidance of an experienced registered dietitian. They can help you figure out the right portion sizes for you and will work with you to reintroduce foods into your diet.

Tips for Successfully Managing IBS with a High-Fiber Diet

Integrating fiber into an IBS diet can be challenging. Here are some tips to help you move toward a high-fiber diet.

Gradually Increasing Fiber Intake

According to the U.S. Dietary Guidelines for Americans (DGA), adults should aim to eat about 22-34 grams of fiber per day. Increase fiber gradually over the course of a few weeks to minimize any unwanted symptoms like gas and bloating.

Balancing Fiber with Adequate Hydration

Fiber absorbs water, so it’s important to increase the amount of water you drink as you eat more fiber. One recommendation is to drink at least 48 ounces (6 glasses) of water everyday as you increase your fiber intake.

How to Use Fiber Supplements Safely

Studies have shown that fiber supplements such as psyllium husk and partially hydrolysed guar gum (PHGG) may aid in the management of IBS symptoms. Taking a fiber supplement could help you meet your daily fiber needs if you’re having trouble getting enough from your diet.

It’s essential to speak with your healthcare provider before starting a fiber supplement, as some may reduce the absorption of certain medications. Fiber supplements should be started at a low dose and slowly increased to test your tolerance.

How Season's Dietitians Can Support Your IBS Management

If you have IBS and need help managing your symptoms with nutrition, a registered dietitian can help! Our IBS dietitians have extensive experience addressing IBS through the use of food and symptom journals, elimination diets, and diet and lifestyle changes. 

A Season dietitian can help you manage IBS symptoms and meet fiber recommendations.