6 clear jars spilling nuts and seeds onto a white surface, what you need to know about fibre and IBS

What you need to know about fibre and IBS

If you are going to try any sort of supplement, always discuss with your doctor and nutrition professional first. This post is for general information purposes only, is not meant to diagnose or treat, and is in no way a replacement for consulting a medical professional.

What is fibre?

Fibre is present in many plant-based foods. In general, it is the non-digestible portion of our food that ends up in our large intestine and instead is food for our friendly gut bacteria. The gut bacteria partially or completely ferment the fibre, producing gas as well as some important nutrients that your body needs. Understanding how and where to get fibre in your diet is important in general, and definitely necessary when it comes to fibre and IBS.

However, the definition can vary based on regionally specific nutrition guidelines, and in some countries (like here in Belgium), substances that act like fibre in the gut are officially grouped into the category of fibre (i.e., resistant starch).

As said, fibre is found in plant-based foods, namely:

  • Whole grains
  • Lentils and legumes
  • Fruits
  • Vegetables
  • Nuts
  • Seeds

Fibre is an incredibly important part of our diet; it helps keep our bowel movements regular and can add bulk to loose stools, as well as loosen up hard stools (sounds contradictory, but we’ll get into this more soon!). This is an important part of our body’s natural detoxification process, getting rid of toxins out of our system as well as other waste products like excess hormones. It can also have a positive effect on blood sugar levels, and increases satiation from a meal, leading to a lower likelihood of overeating.

The general recommendation (which can vary depending on a country’s nutritional guidelines, is that adults should strive for more than 25g of fibre per day, with some recommendations saying that we should be consuming at least 30g of fibre per day. Studies have shown a positive relationship between consuming 25-29g of fibre per day and a reduction in risk for coronary heart disease, type 2 diabetes, colorectal cancer, and all-cause mortality when compared to people eating less than this amount.

A bowl of salad with many brightly coloured vegetables all around, what you need to know about fibre and IBS

The categories of fibre that you should know about

There are different ways to categorize types of fibre, but the most used and most relevant when it comes to IBS is soluble and insoluble types. Foods usually contain both types of fibre at the same time but can be more dominant in one over the other.

Soluble fibre

This type of fibre will dissolve (is soluble) in liquids. In our gut it forms a gel-like substance (imagine it on a much smaller scale to the gel-like properties of chia seeds when immersed in liquid).

Soluble fibre slows the transit time of our food through our digestive system which can help stabilize blood sugar levels, keep you feeling satiated for longer following a meal, and allow adequate time for your body to absorb nutrients. Because it attracts water, like a sponge, it helps soften stool.

Soluble fibre can be found in:

  • Some vegetables & fruit
  • Oats
  • Lentils & legumes
  • Nuts
  • Seeds

Insoluble fibre

In contrast to soluble fibre, insoluble fibre does not dissolve in liquids. It helps add physical bulk to the stool and speeds up the transit time of our food through our gut.

Insoluble fibre can be found in:

  • Wheat bran
  • Rice bran
  • Fruit & vegetable skins
  • Nuts
  • Seeds
  • Lentils & legumes
  • Whole grains


What’s the deal with fibre and IBS?

It was previously thought (and indeed still talked about in many spaces) that a low fibre diet could be a cause behind IBS. Because of this, a lot of health professionals still tend to advise people with IBS to increase their fibre intake. While not eating enough fibre is definitely an issue amongst the general public, it’s not quite so black and white when it comes to IBS.

Fermentability of fibre

Many types of fibre tend to be high fermentable by the bacteria in our gut. In general, this is a good thing as this keeps our gut bacteria healthy and in a good balance. However, when it comes to IBS this is likely a contributing factor to symptoms flaring up. The fibre sources that fall into this category are thus also considered part of the FODMAP-family (but not all FODMAPs are sources of fibre).

Soluble fibre tends to be highly fermentable whereas insoluble fibre tends to be low- or moderately fermentable and therefore better tolerated. It’s not necessarily a hard-and-fast rule, however, so it definitely takes time to discover what works and what doesn’t for your body.

Some examples of good sources of (low-FODMAP) fibre for IBS:

  • Chia seeds (2 tbsp = 8g of fibre)
  • Green kiwi, peeled (2 small kiwis = 6g of fibre)
  • Firm tofu (160g = 6g of fibre)
  • Oats (50g = 5g of fibre)
  • Flaxseeds (1 tbsp = 4g of fibre)
  • Raspberries (60g = 3g of fibre)
An assortment of many brightly coloured vegetables, what you need to know about fibre and IBS

Should you be supplementing with fibre for IBS?

If you are going to try any sort of supplement, always discuss with your doctor and nutrition professional first. This post is for general information purposes only, is not meant to diagnose or treat, and is in no way a replacement for consulting a medical professional.

In general, research has shown that getting sufficient fibre from your diet is more beneficial that fibre from supplementation. This is namely because our foods contain various types of fibre giving a wider range of benefits, whereas supplementation tends to be focused on specific types of fibre in isolation.

However, if you are struggling with fibre intake and experiencing a high amount of IBS symptoms, supplementation could be something to discuss with your health care team. The type of supplementation is going to be unique to the individual and what type of IBS symptoms you tend to have. Currently there is not much convincing results from research studies in order to give proper direction in IBS recommendations. 

Whether you’re starting with supplements, or just looking to increase your fibre intake with real foods, make sure to do so gradually, as a dramatic increase from one day to the next will likely result in significant digestive issues as your system isn’t used to these amounts. In addition, be sure to drink sufficient quantities of water – without proper hydration fibre can end up having the opposite effect of what is intended.

Type of fibre sources/supplements and IBS

Psyllium husk: tends to be well tolerated by people with IBS and research indicates it may be helpful for constipation.

Oats / oat bran: may be helpful for improving constipation, abdominal pain, and bloating but more studies are needed.

Flaxseeds: similar findings as with oats, up to 1 tbsp per day is considered low-FODMAP (flaxseeds are also a great plant-based source of Omega-3!).

Resistant starches: this type of prebiotic fibre tends to ferment slower throughout the entire length of the large intestine. Because of this, it may produce less gas-related symptoms. However, it hasn’t been shown to be helpful in regulating bowel movements.

Partially hydrolysed guar gum: has prebiotic properties and may be well tolerated in IBS for both constipation and diarrhea; however, more studies are needed. 

Sterculia: this non-fermentable source of fibre has gel-forming properties and may help with stool softening for constipation; however, more studies are needed.

Wheat bran: contains a high amount of fructans (a type of FODMAP) and may worsen IBS symptoms.

Wheat dextrin: no studies conducted in regard to IBS.

Inulin: highly fermentable type of fibre and may worsen gas.

Fructo-oligosaccharides & galacto-oligosaccharides (FOS/GOS): a type of highly fermentable fibre (FODMAP) and may worsen IBS symptoms.


The bottom line…

It’s not possible to give sweeping recommendations for fibre when it comes to IBS, regardless of the sub-type you may have. It’s always best to work with a health and nutritional professional to identify what foods will work best for you and your body.


El-Salhy, M., Ystad, S. O., Mazzawi, T., & Gundersen, D. (2017). Dietary fiber in irritable bowel syndrome (Review). International journal of molecular medicine, 40(3), 607–613. https://doi.org/10.3892/ijmm.2017.3072 

Reynolds, A., Mann, J., Cummings, J., Winter, N., Mete, E., & Te Morenga, L. (2019). Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet (London, England), 393(10170), 434–445. https://doi.org/10.1016/S0140-6736(18)31809-9 



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