Can a fibre supplement help people with irritable bowel syndrome (IBS) who are following a low FODMAP or modified FODMAP diet? Before we answer this question it is important to address what fibre is, where to find fibre, what the benefits of fibre are and when our diet is at risk of being low in fibre.
What is fibre?
Fibre is a key carbohydrate component of all plant foods (e.g. fruits, vegetables, grains and legumes) that is not digestible.  Instead, fibre performs many other functions that help to keep the gut and the rest of the body healthy. Different fibre types exist, namely insoluble, soluble and prebiotics (including resistant starch).
Where is fibre found?
Foods naturally contain a mixture of many different types of fibre, so getting fibre from a variety of food sources such as wholegrains, fruits, vegetables, nuts and legumes everyday is ideal. By contrast, fibre supplements generally contain one specific type of fibre and may be useful when adequate fibre intake from food sources alone is difficult.
The benefits of fibre
Fibre plays many important roles in the body, including everything from regulating bowel habits (e.g., relieving constipation), providing fuel for the gut microbiome and normalising blood sugar and cholesterol levels. Dietary fibre comes in many different shapes and sizes and different types have distinctly different effects on the body. For example, one type of fibre may be particularly good at regulating blood sugar levels, but have minimal effects on bowel habits or vice versa.
The risk of a diet low in fibre
When there is a type of food eliminated/restricted from someone’s typical diet there is a potential risk of reducing important macro- or micronutrients - fibre is one of them. As you may know, by reducing FODMAPs in the diet there is a potential risk of reducing overall fibre intake. This occurs particularly when key fibre sources containing wheat, rye, barley and legumes are limited in a low FODMAP diet. It is recommended that Australians consume 25-30g of dietary fibre per day, however currently, average intakes sit well below recommendations. 
The suitability of fibre supplements for people with IBS depends on the physiological characteristics of the fibre they contain - for example the fibre’s solubility in water, water holding ability and fermentability - or the potential to contribute to gas production in the large intestine. Although a considerable number of studies have been conducted to measure the effects of fibre supplementation in people with IBS , interpreting their findings is not always easy.
Below is a summary of the evidence for the use of fibre supplements in IBS:
|Fibre supplement type||Recommendations for use in people with IBS|
|Psyllium||Appears to be well tolerated by many people with IBS. Studies indicate that it may be especially useful in relieving constipation in people with IBS-C. However, psyllium may not be tolerated by all.|
|Wheat bran||Existing studies suggest that wheat bran is ineffective at normalising bowel movements and may worsen symptoms in people with IBS.|
|Oats/oat bran||May improve constipation, abdominal pain and bloating in people with IBS, but more studies are needed.|
|Linseeds/linseed meal||Up to 2 tbs/day may improve constipation, abdominal pain and bloating in people with IBS, but more studies are needed.|
|Wheat dextrin||Has not been formally studied in IBS.|
|Inulin||Highly fermentable and may worsen gas related symptoms in people with IBS.|
|Fructooligosaccharides (FOS)/galactooligosaccharides (GOS)||Rapidly fermentable and may worsen gas related symptoms in people with IBS.|
|Resistant starch||Slowly fermented along the whole length of the large intestine, so may produce less gas related symptoms than other highly fermentable fibres (e.g. FOS, GOS and inulin) in people with IBS. Has prebiotic properties, but is not necessarily helpful for normalising bowel movements.|
|Partially hydrolysed guar gum (PHGG)||Existing studies indicate that PHGG may be well tolerated and helpful in people with both IBS-C and IBS-D, but more studies are needed. Has prebiotic properties, which may be beneficial for gut health.|
|Methylcellulose||May be especially helpful in IBS-C as it is non-fermentable and has gel-forming properties that help with stool softening. More studies are needed to confirm these proposed benefits.|
|Sterculia||May be especially helpful in IBS-C as it is non-fermentable and has gel-forming properties that help with stool softening. More studies are needed to confirm these proposed benefits.|
Tips for using fibre supplements when you have IBS: