Make Friends with Fibre

Dietary fibre is an important ‘macronutrient’ that although it doesn’t provide any energy, it has many benefits, including playing a big role in keeping the digestive system happy and healthy. It is something that we should all be trying to consume in adequate amounts every day for both gut and overall health.

So, what is fibre? Dietary fibre is the collective term for the part of plant foods that our body can’t breakdown. There are three main types of dietary fibre; soluble, insoluble and resistant starch. Plant foods naturally contain a combination of these three varieties of fibre. Each type of dietary fibre has a different structure and varying species of our gut microbes favour different fibres. We should aim to consume 25-30g of fibre daily from a wide variety of sources to help our gut microbiome be as diverse as possible.  

Functions and sources of different types of dietary fibre: 

• Soluble fibre: Soluble fibre is highly fermentable and soaks up fluid in the gut to form a gel. This helps keep the stool soft and reduce diarrhoea. It also aids satiety, blood sugar level control and lowering blood cholesterol, by binding with it and preventing its absorption. Sources of soluble fibre include; fruit, vegetables, oats, nuts and legumes.
• Insoluble fibre: Insoluble fibre aids stool mass and improves gastrointestinal tract motility and bowel movement regularity – important if you experience constipation. It also provides fuel for the healthy bacteria in the gut. Sources of insoluble fibre include; wholegrains, seeds and skins of fruit and vegetables. 
• Resistant starch: As the name suggests, resistant starch ‘resists’ digestion in the small intestine and travels through to the colon intact. Once it reaches the colon, it is fermented by the bacteria – acts as food for the healthy gut bacteria and produces short-chain fatty acids which are extremely beneficial for our health. Sources of resistant starch include; cooked and cooled potatoes, rice and pasta, green bananas and legumes.

Should I be taking a fibre supplement? 

As mentioned above, foods naturally contain a mixture of different types of fibre whereas fibre supplements generally only contain one specific type of fibre (i.e. psyllium husk). To ensure we are feeding a range of different gut bugs, we want to try to eat as diversely as possible as each strain of bacteria prefers different types of fibre. However, if you’re someone who struggles to consume adequate fibre from food alone, a fibre supplement is a cost-effective way to increase your intake. 

What does this mean for IBS? 

As fibre is unable to be digested by the body, it is fermented in the large intestine, causing large amounts of gas to be produced in a relatively short amount of time. This may lead to further exacerbation of IBS symptoms. These fibre sources don’t have to necessarily be FODMAPs to cause an exacerbation of symptoms. An example of this is resistant starch. However, there are types of fibre, such as psyllium and oats, that are less ‘gas forming’, thus they may be tolerated better by IBS patients.

Research has even shown soluble fibre to be useful in improving overall IBS symptoms. A general recommendation to increase overall fibre may be detrimental due to the possible worsening of symptoms. It is recommended that IBS patients work with an accredited practising dietitian who can help guide you around fibre intake and symptom management.

Reference list: 

1. Dr Bridgette Wilson. Could different types of fibre have unique effects on our gut bacteria? 2019. The Gut Health Doctor. Available from: https://www.theguthealthdoctor.com/all-articles/different-types-of-fibre 

2. Everyday Nutrition Australia. Fibre & a Low FODMAP diet. 2020. 

3. NHMRC. Nutrient Reference Values. 2020. Australian Government. Available from: https://www.nrv.gov.au

4. So D. Research Update: Dietary fibre in the era of microbiome science. Monash University. 2019. Available from: https://www.monashfodmap.com/blog/research-update-dietary-fibre-era- microbiome-science/

5. McNamara L, Iacovou M. Fibre supplements & IBS. Monash University. 2017. Available from: https://www.monashfodmap.com/blog/fibre-supplements-ibs/

6. El-Salhy M, Ystad S.O, Mazzawi T, Gundersen D. Dietary fiber in irritable bowel syndrome (Review). Int J Mol Med. 2017; 40(3): 607-613. Doi: 10.3892/ijmm.2017.3072 

7. Reynolds A et al. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet. 2019; 393(10170): 434-445. doi: 10.1016/S0140-6736(18)31809-9