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IBS & Fiber: How Do I Get Enough?

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If you have ever mentioned gastrointestinal issues to your doctor, then they have likely talked to you about your fiber intake. This is for two reasons. First, Americans, in general, are sorely lacking in their fiber intake (10-15 grams/day on average). Second, fiber is incredibly important for gut health!  If you are dealing with Irritable Bowel Syndrome (IBS), then the type and amount of fiber that your doctor may recommend will vary. Let’s take a look at what exactly fiber is, where you can get it, and how it may help your IBS.

 

Fiber: Soluble vs. Insoluble

Fiber is a type of carbohydrate that cannot be digested. It comes from all different types of plant foods like fruits and vegetables, nuts, seeds, legumes, and whole grains. There are also synthetic fiber supplements, like wheat bran and psyllium husk. There are two types of fiber: soluble and insoluble. Many plants contain both types of fiber (which is a good thing!) but let’s talk about the difference.

Soluble fiber dissolves in water and turns into a gel-like substance in your gastrointestinal tract. From a gut health perspective, it attracts water and bulks in your system as well as slows things down from moving too quickly through your GI system. Soluble fiber is beneficial for other things like blood sugar control and lowering cholesterol. Foods that are high in soluble fiber include oats, chia seeds, apples, pears, black beans, sweet potatoes, and avocados.  

Insoluble fiber adds bulk to your stool and helps stool move through smoothly. Unlike soluble fiber, it does not dissolve in water. Foods that are high in insoluble fiber include whole-wheat flour, wheat bran, nuts, and vegetables like cauliflower and potatoes. 

 

How much fiber should I be getting?

As previously stated, most Americans only get about 15 grams of fiber per day! The goal for most people is 25-35 grams per day. If you’re not currently getting enough, there are two ways to increase your fiber intake: food and supplements. As a Registered Dietitian, I typically encourage patients to try increasing their fiber from food intake first, but a targeted fiber supplement can often be a game-changer for many people with IBS.

When increasing your fiber intake, either through food or a supplement, it’s imperative to do so very slowly! If you increase your intake too quickly, you risk an increase in your uncomfortable gastrointestinal symptoms like gas, bloating, abdominal pain, or constipation. Definitely not the result that you were looking for!

A good rule of thumb is to increase your fiber intake by about 5 grams per day. If you’re nervous about creating symptoms, go slower. Fiber also requires adequate water intake, so aim for at least 8 glasses per day (but 10-12 glasses are even better). 

I highly recommend working with a healthcare provider if you have IBS and want to try a fiber supplement. In those that suffer from constipation, adding in too much fiber or the wrong type can be like adding fuel to the fire, i.e. it may back you up even more. Working with a knowledgeable professional can help you evaluate your current diet and fiber intake to ensure that you’re adding the right supplement. 

 

How do I increase fiber with IBS?

Fiber is extremely important for general gut health but can be an absolute game-changer for those with IBS as it can resolve many symptoms. When I make fiber recommendations to my patients, I take into account whether or not they are doing a Low FODMAP diet, if they are already aware of certain food triggers or if they’re newly diagnosed and starting from scratch. The following are my tips for each scenario:

  • Low FODMAP fiber:
    • When I’m counseling patients on the low FODMAP diet, we also discuss the importance of fiber. It can be very easy to decrease your fiber intake during the diet as many high fiber foods are off-limits. I highly recommend utilizing smaller, low FODMAP serving sizes of foods like chickpeas, lentils, beets, edamame, and blueberries.
    • Add in seeds! My patients will tell you that I am a seed fanatic. Most are low FODMAP, they’re high in fiber and you can add them to so many things (ex: oatmeal, yogurt, energy bites, cookies, salads, trail mix, etc). Low FODMAP seeds include chia, pumpkin, sunflower, hemp, and sesame. Ground flaxseeds are also fantastic but they do have a high FODMAP serving. 
    • Be wary of products that have added fiber (i.e. certain granola bars, cereals, snacks, etc) like inulin or chicory root fiber. 
    • Supplement: They are many low FODMAP fiber supplement options available. These include psyllium husk, sunfiber, methylcellulose, and acacia. 
  • Known food triggers:
    • If you have already identified your FODMAP triggers, then focus on other groups that you did not react to. Example: Mannitol is found in foods like cauliflower, sweet potatoes, mushrooms, and butternut squash. You can still focus on smaller, low FODMAP-friendly servings of most of these foods but work on increasing your intake of other groups. Great options include garlic and onions (which are also prebiotic fibers), whole wheat bread and pasta, and cruciferous vegetables like brussels sprouts and beans. 
  • If you're newly diagnosed:
    • Take your time: do not go from eating a minimal fiber diet to a high fiber diet. Your body will be in for a rude awakening and you’ll likely experience increased gastrointestinal symptoms like gas, bloating, abdominal pain, constipation, and/or diarrhea. 
    • Experiment with swaps: try swapping out lower fiber foods for their high fiber alternatives. Things to try: whole grain bread instead of white, and quinoa instead of white rice. Add in a piece of fruit or a side of veggies with your meals. Add in nuts or seeds to your afternoon snack. It’s not a bad idea to take note of any symptoms that occur when you’re adding in some of these foods. That way, if you do decide to try a low FODMAP diet, you’ll have a better idea of possible triggers.
    • Stay hydrated: increased fiber without increased fluid intake is not advised. Buy a big water bottle and refill a couple of times per day. Keep a glass of water by your bedside table and drink when you wake up. Focus on hydrating foods like smoothies, soups, cucumber, strawberries, and oranges. 

 

The most recent American College of Gastroenterology IBS Guidelines recommends soluble fiber for those with IBS. Certain fibers ferment in the colon or have poor water holding capacity. This can make IBS symptoms worse by producing gas, bloating, or diarrhea/constipation. A good soluble fiber supplement is psyllium husk (like the popular brand, Metamucil, for example) and you can take it as a powder or pill. Remember to talk about starting any fiber supplements with your healthcare provider, as they can help tailor the right approach for you. 

 

References

“Dietary Fiber: Essential for a Healthy Diet” mayoclinic.org. Mayo Clinic, January 6, 2021. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fiber/art-20043983

Lacy, Brian E. PhD, MD, FACG1; Pimentel, Mark MD, FACG2; Brenner, Darren M. MD, FACG3; Chey, William D. MD, FACG4; Keefer, Laurie A. PhD5; Long, Millie D. MDMPH, FACG (GRADE Methodologist)6; Moshiree, Baha MD, MSc, FACG7 ACG Clinical Guideline: Management of Irritable Bowel Syndrome, The American Journal of Gastroenterology: January 2021 - Volume 116 - Issue 1 - p 17-44 doi: 10.14309/ajg.0000000000001036 

McManus, Katherine, D. “Should I Be Eating More Fiber?” health.harvard.edu. Harvard University Publishing, February 27, 2019. https://www.health.harvard.edu/blog/should-i-be-eating-more-fiber-2019022115927




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About Author

Liz McMahon, RDN, LDN
Liz McMahon, RDN, LDN

Liz is a Registered Dietitian who focuses on digestive health. She has completed FODMAP training through Monash University and loves seeing the benefit her IBS patients have with this diet! Liz has been in the nutrition field for over 10 years, working at a top hospital in Philadelphia as a Clinical Dietitian for the past 5 years. She also runs her own private practice, Liz McMahon Nutrition, where she provides virtual nutrition counseling to clients with a range of gastrointestinal disorders.

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