Fibre and gastrointestinal disease – does the type of fibre matter?
Dietary fibres, as defined by Codex Alimentarius1 and the European Commission2, are carbohydrate polymers with three or more monomeric units, which are neither digested nor absorbed in the small intestine.
Research from epidemiological studies shows that every 7g increase in daily fibre intake is associated with a significantly reduced risk of cardiovascular disease (relative risk (RR) 0.91, 95% CI 0.88-0.94, P<0.001), haemorrhagic plus ischaemic stroke (RR 0.93, 95% CI 0.88-0.98, P=0.002), colorectal cancer (RR 0.92, 95% CI 0.87-0.97, P=0.002), rectal cancer (RR 0.91, 95% CI 0.86-0.97, P=0.007) and type 2 diabetes (RR 0.94, 95% CI 0.90-0.97, P=0.001).3
Despite the benefits of increased fibre consumption, and national guidelines advising that adults consume at least 25g4 (Ireland) and 30g5 (UK) of fibre per day, the average intake is in fact only around 19g/day.6,7
A recent review by Gill and colleagues explores the physiochemical properties (solubility, viscosity, fermentability) of fibres and how these can influence their functional effects in gastrointestinal health, focussing on functional constipation, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and diverticular disease.8
Research has shown that fibre can reduce chronic constipation by increasing stool frequency and normalising stool consistency.9 However, the type of fibre consumed may influence response. Non-viscous, highly fermentable fibres (such as prebiotic fibres like inulin) are broken down by bacteria in the colon and lose their water holding capacity. These types of fibre have not consistently shown a benefit on increasing stool frequency and stool consistency. In contrast, viscous and poorly fermented fibres (such a psyllium) possess a high-water holding and gel-forming capacity throughout the gastrointestinal tract, helping to relieve constipation symptoms.8
Irritable Bowel Syndrome
Guidelines on dietary fibre in IBS management vary; in the UK, NICE recommend that it may be helpful to limit intake of high-fibre foods, reduce intake of resistant starch and discourage eating insoluble fibre (found in foods including wholegrains and nuts10), whereas the World Gastroenterology Organisation recommend a high fibre diet but also recommend that insoluble fibres could be limited as they may exacerbate symptoms.11,12
Research has shown that fibre, in particular soluble fibre (found in foods including fruit and oats10), reduces symptoms of IBS and improves stool frequency and consistency, although results are inconsistent with wide variations in response.13
Inflammatory Bowel Disease
In the past, patients with IBD have been recommended to reduce high-fibre foods during relapse, despite the evidence not supporting this.8
In vitro research suggests fibre could be beneficial in IBD through the production of short chain fatty acids (SCFA) and their role in regulating intestinal inflammation.14-16 Data from human studies is limited, often contradictory, and varies between the disease conditions: ulcerative colitis and Crohn’s disease. Patients with ulcerative colitis may be more responsive to fibre, because of the production of SCFAs at the site of the disease. Nonetheless, patients with IBD should be encouraged to have a varied diet that contains fibre rich foods and monitored for their tolerance, although these foods – such as raw fruits & vegetable, beans, popcorn, seeds, nuts, and whole grains - should be restricted in patients with a stricture if there is a risk of obstruction.8,17
Research has shown an association between fibre consumption and risk of diverticular disease; 5g/day increase in dietary fibre intake is associated with a reduced risk of diverticular disease in women (RR 0.86, 95% CI 0.84-0.88, P<0.0001). However, the source of fibre appears to be important; fibre from fruit and cereals were associated with a reduced risk, fibre from vegetables was not significantly associated, and fibre from potatoes were associated with an increased risk.18
The effects of fibre in diverticular disease are suggested to be by increasing stool bulk and decreasing colonic pressure - therefore reducing herniation.8
Dietary fibre appears to play an important role in a number of gastrointestinal conditions, and although progress in the field has been made, we are yet to know the optimal dose, type and source of fibre that is needed for the management or prevention of gastrointestinal symptoms and disorders.
1. Codex Alimentarius Commission Joint FAO/WHO Food Standards Programme (2004) Proposals for a definition and methods of analysis for dietary fibre content.
2. EU (2011) Regulation (EU) No 1169/2011 of the European parliament and of the Council on the provision of food information to consumers. Official Journal of the European Union L304:18–63
3. SACN (2015) Carbohydrates and Health.
4. FSAI (2011) Scientific Recommendations for Healthy Eating Guidelines in Ireland.
5. PHE (2016) Government Dietary Recommendations: Government recommendations for energy and nutrients for males and females aged 1–18 years and 19+ years.
6. PHE & FSA (2018) National Diet & Nutrition Survey: Results from Years 7 and 8 (combined) of the Rolling Programme (2014/2015 to 2015/2016).
7. IUN Alliance (2011) National Adult Nutrition Survey: Summary Report.
8. Gill et al. (2020) Nature Reviews Gastroenterology & Hepatology doi.org/10.1038/s41575-020-00375-4
9. Christodoulides et al. (2016) Alimentary Pharmacology & Therapeutics 44: 103–116
10. BNF (2018) Dietary Fibre. Available at: https://www.nutrition.org.uk/healthyliving/basics/fibre.html Accessed on 09/02/2021
11. National Institute for Health and Care Excellence (2017) Irritable bowel syndrome in adults: diagnosis and management.
12. Quigley et al. (2015) J Clin Gastroenterol 50(9): 704-713
13. Moayyedi et al. (2014) Am J Gastroenterol 109: 1367–1374
14. Cavaglieri et al. (2003) Life Sci 73: 1683–1690
15. Asarat et al. (2016) Immunol Invest 45: 205–222
16. Smith et al. (2013) Science 341: 569–573
17. Brown et al. (2011) Expert Reviews of Gastroenterology & Hepatology 5(3): 411–425
18. Crowe et al. (2014) Gut 63: 1450–1456