Fibre in irritable bowel syndrome
Adequate fibre intake (ie 25 to 35 g total fibre daily) is recommended for good bowel function and can be particularly useful for patients with constipation-predominant IBS1Lacy, 2021.
The type of fibre ingested is important because some types of fibre can worsen IBS symptoms, particularly bloating and pain. The solubility and fermentability of fibre contributes to its effects on the bowel, including adverse effects. See Types of fibre and their role in irritable bowel syndrome for information about types of fibre and their role in IBSLacy, 2021.
To improve bowel function in patients with IBS, advise patients to:
- gradually increase intake (if low) of fibre from fruit and vegetables, as tolerated
- avoid wheat bran and large quantities of other insoluble fibres that are slowly fermented, or soluble fibres that are rapidly fermented—see Types of fibre and their role in irritable bowel syndromeMoayyedi, 2019Lacy, 2021
- trial a less fermentable soluble fibre supplement (eg psyllium) or a nonfermentable insoluble fibre supplement (eg sterculia). Psyllium is useful for both constipation and diarrhoea (acts as a bulking agent); there is limited data to suggest sterculia also has this effect
- ensure adequate fluid intake to maximise effect of fibreMoayyedi, 2019Lacy, 2021.
If symptoms worsen with fibre supplementation, a low-fibre diet may be trialled to assess if this relieves symptoms.
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Soluble fibre | |
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Examples |
some grains (eg oats, rye, barley, millet, buckwheat) some fruit and vegetables (eg artichoke, onion, garlic) seed husk (eg psyllium husk) cooked (from dried) or canned legumes |
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Effects on the bowel and role in IBS |
dissolves in water forming a thick gel in the intestine, which slows digestion and subsequently prolongs satiety generally has a weak laxative effect and is rapidly fermented in the terminal ileum and proximal colon causing gas, flatus and other gastrointestinal symptoms. Less fermentable (long chain) soluble fibre (eg psyllium, some other seeds of plants, oats) has a good laxative effect and is better tolerated in IBS, with some (weak) evidence for efficacy |
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Insoluble fibre | |
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Examples |
most whole grains (eg whole wheat, wheat bran, brown rice, rye, quinoa, wholegrain cereals, wholemeal or mixed-grain products) skins of fruit and vegetables nuts and seeds raw lentils, kidney beans and chickpeas |
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Effects on the bowel and role in IBS |
the hard outer skins and surfaces of roots, grains and seeds, which add bulk to the stool to promote regular bowel function generally has a good laxative effect and reduces intestinal transit time. Insoluble fibre is either slowly fermentable or nonfermentable slowly fermentable insoluble fibre (particularly wheat bran) is not effective for IBS due to excessive gas and bloating (possibly due to fructans) and should be avoided nonfermentable insoluble fibre (eg the skins of fruit and vegetables, some nuts and seeds, other whole grains, sterculia) may be useful in IBS due to decreased potential for gas production, but evidence is lacking |
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Resistant starch | |
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Examples |
cooked and cooled pasta, rice, potatoes firm bananas Hi-Maize (present in commercial products such as breads and cereals) |
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Effects on the bowel and role in IBS |
resists digestion in the small intestine; bacterial fermentation in the large intestine produces short-chain fatty acids, which may promote colonic health, but can contribute to gas and flatus. There are limited well-designed studies to assess tolerance in IBS |
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Note:
IBS = irritable bowel syndrome | |