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For optimal gut health, fibre is the most important nutrient to have on your radar.
Dietary fibre comes with numerous health benefits, both inside and outside of the gut. It helps to regulate your bowel movements, and reduces your risk of developing many chronic diseases including heart disease, type 2 diabetes, and colorectal cancer.
Fibre is also a food source for your gut microbes. One very important job the trillions of microbes living in your large intestine have, is to maintain its mucosal lining. A thicker, stronger mucosal lining means a more robust barrier between your body and any pathogens (‘bad’ bacteria) passing through your gut.
Feeding your gut microbes with adequate fibre helps them to thrive so they can properly protect your intestines.
As alterations to the gut microbiota is postulated as being one of the contributing factors of IBS, it makes sense that we need to eat more fibre in order to support a healthy gut microbiota.
However, it’s not always just as simple as that! When you have IBS, fibre can be both a friend and a foe.
What exactly is fibre?
Fibre is a type of carbohydrate that largely escapes digestion in the stomach and small intestine, making its way mostly intact to the large intestine, where your gut microbes have their feast.
Fibre is found exclusively in plant foods – fruits, vegetables, grains, legumes, nuts and seeds.
There are two main types of fibre; soluble fibre and insoluble fibre, and it can further be characterised as being either fermentable or non-fermentable.
To get even more granular, there are many different classes of fibre, some of which you may have heard of: beta-glucans, cellulose, inulin, pectin and resistant starch (to name just a few!).
How much fibre do we need to eat?
The recommendation in the UK is that we should consume at least 30g of fibre every day.
Sadly, it’s estimated that less than 10% of people achieve this target, and on average we’re consuming about 17g a day; a little more than half.
It’s a similar story the world throughout – the vast majority of people don’t eat enough fibre.
How fibre affects IBS
As I’ve already touched upon, fibre can be described as being either soluble or insoluble.
Soluble fibre dissolves in water to form a gel, and in doing so, it slows down transit time and helps firm up stools. Soluble fibre can also help you pass stools more easily, thanks to its mucilaginous (gel-like) properties.
Insoluble fibre, on the other hand, adds bulk to your stools, but speeds up transit time, so has a mild laxative effect.
Depending on your IBS subtype – diarrhoea predominant IBS (IBS-D) or diarrhoea predominant IBS (IBS-C) – modifying your fibre intake can be very helpful for regulating your bowel movements and reducing symptoms.
Fibre and IBS-D
A lot of people with IBS-D think they can’t tolerate fibre at all, but it may just be that you need to eat less insoluble fibre and more soluble fibre.
Reduce insoluble fibre found in whole grains with the bran intact, some veggies like kale and cauliflower, and fruits with edible seeds like raspberries.
Increase soluble fibre – good low FODMAP options are oats, carrots, oranges and ground flax seed (1 Tbsp flax at a time for a low FODMAP serving).
It’s still really important to get your 30g fibre a day and to eat a wide variety of fruits, vegetables, grains, beans, lentils, nuts and seeds – low FODMAP if need be.
Most plant foods contain a combination of both soluble and insoluble fibre, so the emphasis is on reducing your insoluble fibre intake, not removing it entirely.
Fibre and IBS-C
As mentioned above, most plant foods contain a combination of both soluble and insoluble fibre, which are both helpful in managing IBS-C.
One of the easiest ways you can reduce and prevent constipation is by eating 30g of fibre every day, so if you’re not currently getting this amount, try to increase slowly until you hit the target (try an extra 5g/day for one week, before increasing by another 5g/day the following week until you get to 30g/day).
If you’re increasing your fibre intake, then you’ll probably need to drink more water too, as fibre depends on water to help it move through the digestive tract. Dehydration is a common cause of constipation, so make sure you’re drinking plenty of decaffeinated liquid throughout the day.
Fibre and bloating
Fibre can both prevent and cause bloating.
If you’re not eating 30g of fibre a day, this can contribute to constipation, which in turn can cause bloating.
And if you try to increase your fibre intake too quickly, this can also lead to bloating and digestive discomfort, although this is usually temporary. For some tips on how to avoid this, check out this blog post.
How the low FODMAP diet affects fibre intake
When you reduce the amount of FODMAPs (AKA, fermentable carbohydrates) in your diet, you’re also reducing your intake of dietary fibre too.
This is one of the reasons the elimination phase of the low FODMAP diet is only a maximum of six to eight weeks long.
Research has shown that after just four weeks on the low FODMAP diet, the gut microbiota is negatively affected due to this reduction in fibre intake, particularly prebiotic fibre found in high FODMAP foods like apples, asparagus, wheat, legumes and the allium family (garlic and onions).
Some people find that the low FODMAP diet worsens their constipation, and for others, their diarrhoea goes away, but they become constipated because of the lack of fibre in their diet.
It’s really important not to skip the reintroduction phase of the low FODMAP process so you can expand your diet and increase your fibre intake.
How can you get enough fibre on the low FODMAP diet?
The quick answer is to make sure you’re eating a wide variety of plant foods – fruits, vegetables, whole grains, nuts, seeds and legumes.
The low FODMAP diet doesn’t need to mean low fibre, but if you’re eating a typical Western diet with average fibre intake, then you may have to do a little planning to make sure you’re eating what your body needs.
Here are some of the best low FODMAP fibre sources to include in your diet:
- Kiwi fruit (150g or 2 small fruits, peeled)
- Passionfruit (46g or 2 small fruits)
- Orange (130g or 1 medium)
- Pineapple (140g or 1 cup)
- Raspberries (60g or 30 berries)
- Pomegranate arils (45g or 1/4 cup)
- Broccoli (75g or 3/4 cup)
- Carrot (75g or 1 medium)
- Spinach (75g or 1 1/2 cups)
- Parsnip (75g or 1 medium)
- Potato with skin (200g or 1 medium)
- Red bell pepper/capsicum (74g or 1/4 of a pepper)
- Popcorn (60g or 3.5 cups)
- Buckwheat groats (135g or 3/4 cup, cooked)
- Oats (52g or 1/2 cup)
- Soba noodles (90g or 3oz)
- Brown rice (180g or 1 cup, cooked)
- Quinoa (155g or 1 cup, cooked)
Nuts, Seeds & Legumes
- Chia seeds (24g or 2 Tbsp)
- Tofu and tempeh (160g or 5oz)
- Flax seeds (15g or 1 Tbsp)
- Tahini (30g or 2 Tbsp)
- Chickpeas (42g or 1/4 cup)
- Walnuts (30g or 10 halves)
Food sources of fibre are preferred over supplements, but if you’re struggling to get your 30g a day, psyllium husk is usually well tolerated by people with both IBS-C and IBS-D, as it doesn’t ferment in the gut.
Eat 30g of fibre a day, within your tolerance threshold, and modify your fibre intake as needed.
If you need help increasing or modifying your fibre intake, consider working with an IBS specialist who can guide you through making healthy dietary changes that ensure your nutritional needs are met. while also reducing your uncomfortable and embarrassing gut symptoms.
- Barber TM, Kabisch S, Pfeiffer AFH, Weickert MO. The Health Benefits of Dietary Fibre. Nutrients. 2020; 12(10):3209. https://doi.org/10.3390/nu12103209
- Heidi M. Staudacher, Miranda C. E. Lomer, Jacqueline L. Anderson, Jacqueline S. Barrett, Jane G. Muir, Peter M. Irving, Kevin Whelan, Fermentable Carbohydrate Restriction Reduces Luminal Bifidobacteria and Gastrointestinal Symptoms in Patients with Irritable Bowel Syndrome, The Journal of Nutrition, Volume 142, Issue 8, August 2012, Pages 1510–1518, https://doi.org/10.3945/jn.112.159285