Fibre - The Most Underrated Nutrient

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For the summary & take-home message CLICK HERE

Everybody is always looking for ways to reduce their risk of disease, live longer and live a better, healthier life. What if I told you that not only is there a nutrient that can achieve these aims, but also that this nutrient is very easy to incorporate into your daily life and won’t cost you a fortune? This nutrient is Fibre, something that was always a cornerstone in the diet of humans until the Western diet came along. 

Dietary fibre is the part of plant material which is resistant to enzymatic digestion. There are two types of fibre: soluble and insoluble.¹ Soluble fibre attracts water and turns to gel, which helps slow down digestion and is fermented by the gut bacteria. Some examples of soluble fibre are oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables.¹ Insoluble fibre provides faecal bulk, stimulates bowel movement, and adsorbs undesirable colonic contents (eg, certain xenobiotics) ensuring their removal along with faecal matter. They can, however, also be fermented to varying degrees.² Some examples of insoluble fibre include whole-wheat flour, wheat bran, nuts, beans, cauliflower, green beans, and potatoes.¹

Just in case you have heard of resistant starch and are wondering where that fits in, resistant starch can be soluble or insoluble. If you haven’t heard of resistant starch, it is a starch resistant to digestion and is fermented by gut microbes. However, different types of resistant starches show different fermentability in different areas of the colon or can be fermented by different bacteria within the gut.² The by-products of the fermentation of fibre in the gut confer health benefits that extend beyond the gut to the rest of the body.² 

Figure 1: An image which breaks dietary fibre into soluble and insoluble fibre.

High-fibre diets have been associated with a decreased incidence of several types of diseases. Understanding the role of fibre in the body helps us to understand how fibre offers this protective effect… 

Gut Motility 

Gut motility refers to the passage of food from the mouth through the pharynx, oesophagus, stomach, small and large intestines, and out of the body. Dietary fibres add bulk to your stool which increases gut motility and alleviates constipation Both soluble, viscous fibres and insoluble, non-viscous fibres can contribute to improvements in stool consistency and stool weight. Soluble, viscous fibres (for example, psyllium) have a high water-holding capacity which allows them to be resistant to fermentation and form a viscoelastic substance in the gastrointestinal tract. This contributes to softening the stool and increasing its bulk, making it easier to pass. These properties also assist with diarrhoea by firming loose stools and slowing transit time. On the other hand, insoluble, non-viscous fibres (for example, coarse wheat bran) can contribute to improvements in stool consistency and stool weight via the mechanical stimulation of the intestinal mucosa.³

Increases bulk to the diet

A diet that is rich in fibre is normally lower in energy density, lower in fat content, and larger in volume. This larger mass of food takes more time to eat and its presence in the stomach can bring a feeling of satiety sooner and therefore can help control your appetite.¹

Production of short-chain fatty acids (SCFAs)

Fermentation of fibre in the large intestine produces most of the health benefits associated with fibre, both within the gut and beyond. The fermentation of fibre by the gut microbiota results in the production of a variety of compounds with short-term and long-term health benefits that extend to the immune system and organs such as the liver, kidneys and even the brain.²

These compounds include short-chain fatty acids (SCFAs) which stimulate gut motility, maintain the barrier function of the gut wall, and have anti-inflammatory properties. SCFAs are known to increase mineral absorption in the colon (eg, calcium and magnesium), stimulate the growth of beneficial bacteria (eg, bifidobacteria) in the gut (the sharing of metabolites between different microbes) and increase bacterial biomass which can benefit bowel movement.² An additional benefit of SCFA is that they contribute to the balancing of the pH of the intestine.¹

Decreases the glycaemic index of foods

Soluble fibre attracts water and becomes a gel during digestion, trapping carbohydrates and slowing the absorption of glucose into the bloodstream.1,4 This leads to a significant improvement in fasting blood glucose and glucose levels after eating.

Lowers total and LDL cholesterol  

As soluble fibre becomes a gel during digestion, this potentially traps carbohydrates and fat. The fat that is trapped is not able to be absorbed and is excreted with the faeces, lowering cholesterol levels.¹

Regulates blood pressure 

High-fibre foods such as vegetables contain beneficial nutrients that are metabolised into compounds such as nitric oxide, which may improve blood pressure as there is greater bioavailability to be used for vasodilation. An increase in fibre intake can increase the amount of nitric oxide absorbed, which can improve endothelial function and as a result blood pressure.1,5

As we have shown, dietary fibre has many important roles in the body, which explains why dietary fibre has been shown in an extensive number of epidemiological and interventional studies to have important associations with the development and management of various diseases and mortality. Physicochemical characteristics such as solubility, viscosity and fermentability drive different functionalities in the gastrointestinal tract and therefore underpin their therapeutic potential.3,6

Conclusion

Dietary fibre plays a pivotal role in maintaining and enhancing our health, offering a multitude of benefits that extend beyond basic digestion. Its two primary types, soluble and insoluble fibre, contribute uniquely to our body’s well-being. The integration of fibre into our daily diet is not only a return to the nutritional roots of human history but also an accessible, cost-effective strategy for promoting long-term health.

So, what is the take away message?

Dietary fibre has many roles in the body, including gut motility, increasing the bulk of a traditional Western diet, production of short-chain fatty acids (SCFAs), decreasing the glycaemic index of foods, lowering total and LDL cholesterol, and regulating blood pressure. The suggested daily intake of fibre is 28g per day when based on a 2000 kcal/d diet. This can be adjusted depending on your diet, times 0,014 by the number of kcal you consume per day to get your ideal fibre intake. (International Scientific Association for Probiotics and Prebiotics.)7

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References

  1. Kumar J, Rani K. and Datt, C. 2020. Molecular link between dietary fibre, gut microbiota and health. Molecular Biology Reports. Available here: doi:https://doi.org/10.1007/s11033-020-05611-3 
  2. Gill SK, Rossi M, Bajka B, et al. 2021. Dietary fibre in gastrointestinal health and disease. Nature Review Gastroenterology & Hepatology, 18, 101–116. Available here: https://doi.org/10.1038/s41575-020-00375-4
  3. Barber TM, Kabisch S, et al. 2020). The Health Benefits of Dietary Fibre. Nutrients, 12(10), p.3209. Available here: https://doi.org/10.3390/nu12103209 
  4. Hojsak I, Benninga MA, et al. 2022. Benefits of dietary fibre for children in health and disease. Archives of Disease in Childhood, p.archdischild-2021-323571. Available here: https://doi.org/10.1136/archdischild-2021-323571 
  5. Dhingra D, Michael M, Rajput H, et al. 2011. Dietary fibre in foods: a review. Journal of Food Science and Technology, 49(3), pp.255–266. Available here: https://doi.org/10.1007/s13197-011-0365-5 
  6. Barber TM, Kabisch S, Pfeiffer AFH, et al. 2020. The Health Benefits of Dietary Fibre. Nutrients, 12(10), p.3209. Available here: https://doi.org/10.3390/nu12103209 
  7. International Scientific Association for Probiotics and Prebiotics (ISAPP). (n.d.). Prebiotics. Available at: https://isappscience.org/for-scientists/resources/prebiotics/ 
  8. Silver, J. 2023. How to choose cereals with Fiber. Accessible Wellness.  [Accessed 19 Feb. 2024]. Available at: https://jackiesilvernutrition.com/articles/how-to-choose-cereals-with-fiber/
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Nicola Royce

Nicola Royce

Registered Dietitian, Postgraduate Diploma Diabetes

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