“You need more fiber!” …said almost every gastrointestinal (GI) doctor, to almost all of their patients presenting with irritable bowel syndrome (IBS) symptoms.
If you’re dealing with gut issues of any kind, I’d bet $ you’ve probably heard this advice before. (*Sigh.*)
Don’t get me wrong – as a gut health dietitian, I love fiber-rich foods! I lean on foods high in fiber for healthy regularity, satiety, blood sugar balance, healthy gut microbial diversity, and for other reasons. 😎
Fiber is NOT inherently bad for gut health. In fact, it’s essential for most healthy adults!
However, when it comes to reducing and managing IBS symptoms (think: gas, bloat, diarrhea, constipation, etc…) while fiber-rich foods (and/or fiber supplements) are generally helpful in most cases – fiber can sometimes trigger and worsen IBS symptoms.
Let me explain…
Disclaimer: This article was written for educational purposes and should not replace 1-1 medical and nutritional consultation with qualified healthcare providers.
Table of Contents
What is fiber?
Fiber is a type of indigestible roughage (naturally occurring in most plant foods).
Insoluble fiber (which doesn’t dissolve in water) supports our digestion by adding bulk to our stool, aiding in regularity.
Soluble fiber is a type of fiber which dissolves in water, and has prebiotic benefits (feeding and enhancing the growth of healthy probiotic microbes in our gut).
- Recommended reading: Fiber and Probiotics – a Dynamic Duo
Fiber-rich foods
Foods highest in fiber include, but aren’t limited to:
- Fresh fruits and vegetables
- Prunes
- Whole grains
- Beans and lentils
- Nuts and seeds (especially chia seeds and ground flaxseeds)
- Psyllium husks
Recommended reading:
Some foods are fortified with added fiber, from natural sources such as chicory root (Fiber One products are a prime top-of-mind example of this).
Fiber supplements
If your diet is too low in fiber, you may consider fiber supplements.
Some types of fiber supplements are more natural (think: psyllium) while other fiber supplements are more loaded with unnecessary junk additives (looking at you, Metamucil!).
Recommended reading:
Fiber and IBS: research-backed benefits
On paper, experts will insist fiber is your friend if you have IBS. For example, research studies have shown that fiber generally helps:
- Reduce IBS symptoms (1)
- Increase fecal mass and improve bowel regularity (1)
- Acts as a prebiotic, supporting healthy gut diversity (2)
However, it’s important to keep in mind that not all fiber is created equal – and more fiber isn’t always better!
Too much fiber
Most healthy adults, on average, need about 20 to 35 grams of fiber per day, for healthy regularity.
However, too much of a good thing is NOT good!
If your daily fiber intake is exceeding the recommended healthy range, or you increase your fiber intake too rapidly (without enough fluids to flush it through your gut), you could experience some pretty severe abdominal discomfort.
Consuming too much fiber, especially from fiber supplements or foods fortified with added fiber, can result in symptoms such as:
- Bloating and abdominal distention
- Gas
- Abdominal pain
- Constipation
- Stool impaction
- Intestinal obstruction (in severe cases)
Recommended reading: How To Increase Your Fiber Intake And Improve Your Gut Health
Signs fiber isn’t your friend
This is something the internet doesn’t talk a lot about – but it’s something I’ve witnessed countless times in my gut health nutrition clinic!
If you have a fiber intolerance (aka “roughage intolerance”), you’ll likely notice an uptick in the following IBS symptoms after eating higher-fiber foods (or after taking fiber supplements):
- Gas
- Bloating
- Abdominal pain
- Diarrhea
- Stool incontinence
What causes fiber intolerance among IBS sufferers?
In my experience, people who were diagnosed with IBS but don’t tolerate fiber, often actually have one of the following conditions (which often get mis-diagnosed as IBS):
- Small intestinal bacterial overgrowth (SIBO)
- Crohn’s disease (a type of inflammatory bowel disease / “IBD”)
- Colitis (another type of IBD)
- Diverticulitis
Just make sure you aren’t confusing other types of adverse food reactions with fiber intolerance! (Fiber often overlaps with foods high in gluten and/or FODMAPs.)
Fiber versus gluten
In cases of celiac disease and non-celiac gluten intolerance/wheat sensitivity, if you notice you feel worse after eating whole grains (a food source of fiber) such as whole wheat or rye, which contain gluten, you may actually be reacting to the gluten and NOT the fiber!
High-fiber high FODMAP foods
Many IBS sufferers feel better on a low FODMAP diet.
This is noteworthy because if you find that you’re feeling worse after eating certain higher-fiber + higher FODMAP foods such as apples, whole wheat bread, beans, or lentils, consider the possibility that you’re reacting to the FODMAPs in these foods (versus the fiber!).
TLDR: Don’t confuse a fiber intolerance with a FODMAP intolerance.
Consider trying out a low FODMAP elimination diet for at least a few weeks, to see if you can tolerate low FODMAP high-fiber foods (in the correct Monash-approved low FODMAP serving sizes) such as fresh cucumbers, lettuce, and chia seeds.
If you’re still finding these types of foods trigger your symptoms, you could be dealing with a fiber intolerance (and may want to look into consulting your doctor about what’s causing this).
Sucrose, starch, and fiber
High-fiber foods can also overlap with foods high in sucrose and/or starch, which generally aren’t well tolerated among folks with sucrase-isomaltase deficiency.
For example, if your small intestine is lacking the enzymes to break down the maltose from starchy high-fiber whole grains (like oatmeal, whole wheat bread, etc.), you may find that certain higher-fiber whole grains seem to upset your stomach due to an underlying maltose intolerance.
Or if you find that eating a salad that contains high-fiber foods high in sucrose (like carrots) sends you running to the bathroom, it may actually be the sucrose (versus the fiber) in your salad, triggering IBS symptoms.
Recommended reading: 7 Reasons Oatmeal and Oat Milk Can Cause Diarrhea
Fiber and IBS: final thoughts
Getting enough fiber in your diet is important, and beneficial for gut health in most but not all cases!
If you struggle with IBS and find that you feel worse after consuming higher-fiber foods, you may want to consider the following possibilities:
- You may be reacting to the gluten in certain high-fiber whole grains (such as whole wheat, rye, and cross-contaminated oats).
- Certain high fiber foods are also high in FODMAPs, a common IBS symptom trigger.
- Certain high fiber foods may contain other reactive constituents, such as sucrose or starch (which aren’t well tolerated by people with CSID).
- If you find you do have a fiber/roughage intolerance, you may actually be dealing with another GI condition masquerading as IBS (such as SIBO or IBD, which can also often co-occur with adult-onset sucrase-isomaltase deficiency).
Next steps
If you’d like to learn more about how you can navigate IBS and food reactions holistically (whether as a patient or a practitioner), make sure to download my free gut health nutrition guide: 5 Common Diet Mistakes to Avoid When Healing Your Gut (And What to Do Instead)!
XX – Jenna
Thanks Jenna, always helpful info!