I first started questioning the role of fibre in my diet when I was diagnosed with IBS for the first time in 2009
Back then, I was told to cut back on leafy greens, pasta, bread and gluten containing grains. I recall experiencing significant benefits within less than one week. However, due to my lifestyle at the time, I slowly reintroduced most of those foods back into my life as soon as all my symptoms went away.
When my IBS reached its apex in 2018, however, I was put on a strict low FODMAP diet by my GP, which excluded way more food groups than those listed above. After cautiously testing which ones I could reintroduce back into my diet without triggering IBS symptoms, I realised that there were still a whole lot of foods, which I would never eat in my life again, if not on very special occasions (e.g. most grains, alcohol, cherries, watermelon, apricots, mushrooms, just to name a few).
Despite what the mainstream culture seemed to promote, I found out I was better off without fibre, or with just a minimum amount of it.
What is fibre?
Technically, fibre is a subspecies of carbohydrates. Carbohydrates can be thought of as long and complex chains of simpler glucose molecules (made out of carbon, hydrogen, oxygen). Even though carbohydrates are non essential macronutrients (in fact, through a metabolic pathway known as ʻgluconeogenesisʼ, glucose molecules are manufactured in the liver from carbon substrates found in amino acids and lipids), paradoxically, they happen to be the bodyʼs preferred source of energy. Indeed, they appear to be the most accessible source of glucose, which is essential to run vital brain functions, as well as one of the muscle-skeletal energy systems.
Not all carbohydrates, however, are broken down by the body to produce energy, and here is where fibre comes into play: both soluble and insoluble fibre, along with resistant starch, present a molecular structure that our enzymes are unable to break down. The function of fibre, therefore, is not that of providing our body with energy.
Fibre can be soluble or insoluble:
- Insoluble fibre (roughage) passes through our GI and its only function is to create stool volume.
- Soluble fibre and resistant starch are fermented by gut bacteria and dissolved in water, forming a gel in the colon.
Both soluble and insoluble fibre have been popularised in recent years, due to their positive association with: colon cancer reduction; blood glucose reduction; LDL reduction (which might not be as a positive thing as you think, after all, but it would be off-topic now). However, all those positive associations should be rediscussed if you have a GI pathology.
Some literature
Even though fibre (without differentiating between soluble and insoluble) was said to be effective in a small group of Chinese population (33 constipated patients and 20 healthy individuals) who underwent a 4-week kiwi fruit treatment (On On Chan et al. 2007), a causation fibre-relief from constipation is still controversial. In particular, the benefits found in the consumption of a kiwi fruit twice a day could come from water, vitamins and minerals and not necessarily from the fibre itself. A meta analysis of the existing literature from 2012 showed that ʻfiber intake can obviously increase stool frequency in patients with constipation. It does not obviously improve stool consistency, treatment success, laxative use and painful defecationʼ (Yang et al. 2012).
Two studies are worth being mentioned in this regard:
- An interventional study from 1997 (Voderholzer et al) investigated the role of dietary fibre in the treatment of chronic constipation. What was found was a positive outcome in patients with no GI issues, whereas no significant change was seen in the other group: ʻEighty percent of patients with slow transit and 63% of patients with a disorder of defecation did not respond to dietary fiber treatment, whereas 85% of patients without a pathological finding improved or became symptom freeʼ. So, they concluded ʻSlow GI transit and/or a disorder of defecation may explain a poor outcome of dietary fiber therapy in patients with chronic constipationʼ.
- A more recent study from 2012 (Kok-Sun et al) investigated the role of fibre in idiopathic constipation and found no benefits in introducing fibre in the diet. In fact, ʻpatients who stopped or reduced dietary fiber had significant improvement in their symptoms while those who continued on a high fiber diet had no changeʼ. So, the authors conclude, ʻidiopathic constipation and its associated symptoms can be effectively reduced by stopping or even lowering the intake of dietary fiberʼ.
Further Reflections
Gut Dysbiosis
One more thing to be considered is the dysbiosis (microbial imbalance) characterising IBS sufferers and its relation to the efficacy of a low FODMAP diet: according to the most recent hypothesis on IBS, most of the symptoms appear to be triggered by an excess of bacteria in the colon, that can be overfed, when too many prebiotics are ingested, leading to an excess of fermentation, and, therefore, gas and pain (see Lyra and Lahtinen 2012, Collins 2014, Simrén 2014, Shukla et al. 2015, Putignani et a. 2016, Benno et al. 2016, Principi et al. 2018, ).
High FODMAP foods, by definition, are fermentable sugars: some of them (mono and disaccharides) are very small molecules, others are bigger polymers (e.g. polyols), others are long glucose polymers, known as polysaccharides. Fibre and starch are also polysaccharides, which makes it easy to understand why many fibrous or starchy foods also happen to be high FODMAP. However not all polysaccharides are highly fermentable, and nor are all other mono and disaccharides, which explains why some fibrous foods are still tolerated by IBS sufferers.
Soluble and Insoluble Fibre and IBS
Moreover, the tolerance level is individual and depends upon each individual’s unique microbiome. Consuming soluble fibre and resistant starch will obviously increase the chance of the bacteria being overfed, even within the recommended intake for average population.
Consuming insoluble fibre might also aggravate IBS symptoms. Indeed, due to the impaired fermentation in the colon, also the stool transit appears impaired: in so called ‘IBS-D’ (IBS-diarrhoea) sufferers, excess water is drawn and bowel movements are accelerated; by contrast, in so called ‘IBS-C’ (IBS-constipation) sufferers, bowel movements are slowed down. Ingesting a bulking, such as insoluble fibre, might potentially interfere with the transit, especially in the case of IBS-C sufferers, as happened in the populations of the constipation studies discussed above.
SIBO, IBD and Other Conditions
A similar discourse could surely be done in regard to SIBO (Small Intestinal Bacterial Overgrowth), which differs from IBS in that the overgrowth appears to be localised predominantly in the small intestine (it is possible that someone with IBS is also affected by SIBO, whereas someone affected by SIBO might not experience IBS symptoms). In that case, fermentation might occur in the small intestine, at the stage of absorption and assimilation of nutrients, which would in turn be impaired even more by the excess of bacterial population.
Lastly, also IBD (Inflammatory Bowl Disease), an umbrella term describing Crohn’s disease and ulcerative colitis also appears to be characterised by dysbiosis (see Putignani et a. 2016) and therefore might be impaired by a diet high in fibre.
Conclusion
Including both soluble and insoluble fibre in the diet of a healthy individual, with no GI issues, is not only harmless but even beneficial. In the case of IBS, SIBO or IBD sufferers, however, an overconsumption of fibre might aggravate some of the symptoms.
These days we find ourselves surrounded with all kinds of diets and lifestyles, each of them advocating to be ‘the best one’ and/or ‘the most suitable for humans’. Even celebrities popularise certain diets or lifestyles, and other ‘gurus’ claim tons of scientific evidence behind what they promote. It’s important, instead, to understand that not every diet or lifestyle can be suitable for everyone.
To cut a long story short, before jumping into a fad diet, or before making any relevant dietary intervention, please, do your own research and seek professional help.
Need simple, gut-friendly recipes?
My recipes are all low-FODMAP and gut friendly. Make sure you check them out!
References
Benno, Peter; Dahlgren, Atti-La, Befrits, Ragnar, Norin, E., Hellström, P. M., & Midtvedt, T. 2016 . ‘From IBS to DBS: The Dysbiotic Bowel Syndrome’. . Journal of Investigative Medicine High Impact Case Reports. https://doi.org/10.1177/2324709616648458
Botschuijver, Sara; Guus Roeselers; Evgeni Levin; Daisy M.Jonkers; Olaf Welting; Sigrid E.M. Heinsbroek; Heleen H. de Weerd; Teun Boekhout; Matteo Fornai; Ad A.Masclee; Frank H.J. Schuren; Wouter J.de Jonge; Jurgen Seppen; René M.van den Wijngaard. 2017. ‘Intestinal Fungal Dysbiosis Is Associated With Visceral Hypersensitivity in Patients With Irritable Bowel Syndrome and Rats’. Gastroenterology 153(4): 1026-1039. https://doi.org/10.1053/j.gastro.2017.06.004
Collins, Stephen M. 2014. ‘A Role for the Gut Microbiota in IBS’. Nature Review Gastroenterology Hepatology 11: 497–505. https://doi.org/10.1038/nrgastro.2014.40
Lyra, Anna and Sampo Lahtinen. 2012. ‘Dysbiosis of the Intestinal Microbiota in IBS’. In Godfrey Lule (ed.). Current Concepts in Colonic Disorders. Rijeka (Croatia): InTech:261-276.
Yang, Jing; Hai-Peng Wang; Li Zhou; and Chun-Fang Xu. 2012. ʻEffect of dietary fiber on constipation: A meta analysisʼ. World Journal of Gastroenterology 18(48):7378–7383. doi: 10.3748/wjg.v18.i48.7378
Kok-Sun Ho; Charmaine You Mei Tan; Muhd Ashik Mohd Daud; and Francis Seow-Choen. 2012 ʻStopping or reducing dietary fiber intake reduces constipation and its associated symptomsʼ. World Journal of Gastroenterology 18(33):4593–4596. doi: 10.3748/wjg.v18.i33.4593
On On Chan, Annie; Gigi Leung; Teresa Tong; and Nina YH Wong. 2007. ʻIncreasing dietary fiber intake in terms of kiwifruit improves constipation in Chinese patientsʼ. World Journal of Gastroenterology 13(35):4771–4775. doi: 10.3748/wjg.v13.i35.4771
Principi, Nicola; Rita Cozzali; Edoardo Farinelli; Andrea Brusaferro; Susanna Esposito. 2018. ‘Gut dysbiosis and irritable bowel syndrome: The potential role of probiotics’. Journal of Infection 76(2): 111-120. https://doi.org/10.1016/j.jinf.2017.12.013
Putignani, Lorenza; Federica Del Chierico; Pamela Vernocchi; Michele Cicala; Salvatore Cucchiara; Bruno Dallapiccola. 2016. ‘Gut Microbiota Dysbiosis as Risk and Premorbid Factors of IBD and IBS Along the Childhood–Adulthood Transition’. Inflammatory Bowel Diseases 22(2):487-504. https://doi.org/10.1097/MIB.0000000000000602
Simrén, Magnus. 2014. ‘IBS with intestinal microbial dysbiosis: a new and clinically relevant subgroup?’ Gut http://dx.doi.org/10.1136/gutjnl-2013-306434
Shukla, Ratnakar; Ujjala Ghoshal; Tapan N. Dhole; Uday C. Ghoshal. 2015. ‘Fecal Microbiota in Patients with Irritable Bowel Syndrome Compared with Healthy Controls Using Real-Time Polymerase Chain Reaction: An Evidence of Dysbiosis’. Dig Dis Sci 60:2953–2962. https://doi.org/10.1007/s10620-015-3607-y
Voderholzer, Winfried A.; Schatke, Winfried; Mühldorfer, Birgit E.; Klauser, Andreas G.; Birkner, Berndt; Müller-Lissner, Stefan A. 1997. ʻClinical Response to Dietary Fiber Treatment of Chronic Constipationʼ. American Journal of Gastroenterology 92 (1):95-98