FAQ on Dietary Fibres: Digestion, Digestive Tolerance And More
This FAQ aims to address frequently asked questions related to dietary fibres in general and to some specific dietary fibres, e.g. chicory root fibre, for a quick orientation for the reader. If you require more details, please do not hesitate to contact us.
Dietary fibres and their role in healthy eating
What are dietary fibres?
Dietary fibres are mainly classified as carbohydrates that are not digested in the small intestine. This makes the large intestine THE place of action. Here, they are partly or completely broken down by the microbiota (this is called fermentation) or leave the body as a whole via the faeces. Examples for specific dietary fibres are inulin-type fructans (chicory root fibre), plant cell wall material like cellulose, hemicellulose, pectin or beta-glucan and synthesised resistant starches or resistant dextrins.
Are all dietary fibres the same?
No, dietary fibres are a very diverse group of carbohydrates. They differ in the way they occur in a plant or the way they are produced (e.g. synthesised, extracted from plant). Their structure varies depending on the type and number of units (chains) they are built of and how these are linked and branched. They differ in their physical (viscosity, solubility, gel-building properties and more), texturising and sensorial properties. They also differentiate themselves from each other depending on their source. Dietary fibres vary according to their stability and the food matrix they are in, i.e. whether or not the food is cooked or raw. The stability of dietary fibres is especially relevant in food manufacturing processes. Some dietary fibres retain their structure (e.g. chicory root fibres have a very high stability), others undergo changes.
What consequences may the structure difference have?
The structure and nature of a dietary fibre can influence chemical, physical and physiological properties. Fibres can be soluble or insoluble, gel-forming or non-gel-forming, broken down by gut bacteria (partly or completely) or remain intact, add bulk to the content in the large intestine etc. Amongst the fermentable fibres there are a few, such as chicory root fibres (inulin, oligofructose), that have the unique property to be selectively fermented by beneficial gut bacteria like bifidobacteria or lactobacteria, promoting their growthfibre. This effect has been demonstrated in several human intervention studies and has been linked to a proven health benefit, thus qualifying as a prebiotic.
How did fibres become so important in nutrition?
The understanding of the role of fibres in nutrition changed enormously over the last 30 years. Known for a long time as “useless baggage”, researchers discovered the importance of dietary fibres for digestive health and beyond. In addition to increasing stool bulk and improving stool consistency, supporting bowel regularity and other digestive health aspects turned out to be important. Examples are the nourishment of the mucosa of the large intestine, the support of the gut barrier function and more. These functions are mainly related to the fermentation of fibres. The positive influence of dietary fibres on blood sugar or cholesterol lowering effects were also recognised. Today, research focuses on the gut microbiota, how this microbiota is influenced by our daily diet and how its composition can be affected in particular by prebiotic fibres like chicory root fibre. Research is also going beyond digestive health and the gut environment. With the discovery of the so-called “gut-brain axis” scientists realised that the microbiota communicates with other parts of the body via short chain fatty acids (SCFA) and other metabolites that are absorbed into the blood. Via the blood stream those substances reach the brain, the liver, the kidneys, the muscles etc. Influence on weight management, systemic inflammation processes and more are in the focus of research today.
How much and which type of dietary fibre should we eat?
A healthy diet should contain a mix of different types of dietary fibres. The World Health Organization (WHO) recommends a daily fibre intake of at least 25 grams. In the United States intake recommendations are higher, around 32 g/d for male and 27 g/d for female adults (19-50 years of age). [1] Unfortunately, often only about half of what is recommended is actually eaten – a huge and important gap that needs to be closed. In addition to vegetables and grains, fibre enriched foods are an important contribution to bridge this gap.
Feeling the digestion
What are the current consequences of low dietary fibre intake?
Low dietary fibre intake leads to a “silent and lazy gut”. Due to a reduced number of stools per week, unwanted residues of our food stay longer in our gut rather than being excreted as fast as possible. The incidence of constipation is high (more than 20% of the U.S. population), as are the costs for medical treatment of constipation. [2] Chicory root fibres can increase the number of stools per week within a normal range, as demonstrated in human intervention studies [3] and confirmed by a granted health claim in the European Union. [4]
Will I feel the difference if I double the amount of fibre that I usually eat?
Yes, feeling the digestion is ok. In fact, the improved stool frequency and softer stool consistency will be a relief supporting digestive well-being – a proven effect for chicory root fibre. [3, 5]
Depending on individual sensitivity and perception, higher activity in the gut may also become recognisable but not bothersome, e.g. flatulence. It’s a normal physiological process and logical consequence of fibres (all types of fibres) being present in the gastrointestinal tract. Flatulence is a good sign when it comes to digestive well-being and stands for beneficial gut activities contributing to an improved well-being. Everyone’s perception is different and therefore, fibre intake should be individually adjusted. If disturbed by individual sensations from a higher activity in the gut, the dietary fibre intake should be reduced, accompanied by a step-by-step increase over time. This gives the body time to adapt. Most gases produced by the body are exhaled and not noticed at all. Consuming more fibre also means more content in the lumen of the gut which “stretches” the gut and may be noticed as “more activity”.
Do in vitro or in vivo hydrogen measurements provide information on the subjective feeling of the digestion process in humans?
No, not at all. Hydrogen production indicates fermentation but is no indicator for subjective feelings of the digestion process. Linking these two aspects does not reflect the ongoing complex processes and interactions in the human body. The vast majority of gas produced by the body is eliminated unnoticed via the breath.
Does an artificial simulation of the gastrointestinal tract indicate actual feelings of digestion in the human body?
No, it does not. Such a simulator, which uses different vessels for each part of the digestive tract, is a closed system while the human body and its gut are a very complex and interactive system. The simulation, which takes place outside the human body, does not allow for quantitative conclusions of tolerance or implications for subjective feelings to be drawn.
How can we evaluate digestive tolerance of dietary fibres?
Reliable information can be retrieved by measuring subjective ratings in large human intervention studies. Summarising data from a large number of studies evens out individual variations in gastrointestinal perceptions and is a comprehensive approach for reliable conclusions. Any study design and interview question or questionnaire on gastrointestinal feelings influences the reporting of these ratings – independent of the food consumed.
Dietary fibre and the gut microbiota
Where is the link between the gut microbiota and dietary fibres?
The gut microbiota lives on food residues that bypass absorption. Those residues function as feed for the microorganism. Proteins are favouring those microorganisms that are involved in proteolytic fermentation. Proteolytic fermentation is known to lead to a number of potentially toxic and harmful metabolites. Contrary to that,saccharolytic fermentation significantly increases amounts of lactate and short chain fatty acids (SCFA), reduces the pH and influences the gut environment positively. Prebiotic dietary fibres, i.e. chicory root fibres (, oligofructose) and galactooligosaccharides (GOS), are triggering a saccharolytic fermentation. In addition, prebiotics are the preferred feed for some types of microorganism, in particular bifidobacteria and lactobacteria, which are beneficial bacteria. Prebiotics promote a faster growth of these beneficial bacteria and thus increase their overall presence, their growth is selectively stimulated. This shift in the microbiota composition is linked to a number of health benefits. [6, 7]
Prebiotic fibres and their uniqueness
What does prebiotic exactly mean?
According to the latest definition from 2017, experts in the field describe a prebiotic as “a substrate that is selectively utilized by host microorganisms conferring a health benefit”. [6] This means that prebiotics support the selective growth of beneficial bacteria in the gut and by doing so provide additional health effects on the body.
Is prebiotic and probiotic the same?
Both terms stand for the support of digestive health and beyond. The International Scientific Association for Probiotics and Prebiotics (ISAPP) explains them as follows and also provides informative infographics for download on their website. [8, 9]
• What are prebiotics?
“Simply put, they are food for beneficial microbes that live on or in us. They are metabolized by the ‘good’ gut microbes, positively impacting the gut environment, with an overall health benefit.”
They feed our natural gut flora.
• What are probiotics?
“Probiotics are live microorganisms that when taken in sufficient amounts can provide health benefits. Sometimes, but not always, they are similar to microbes that normally colonize our bodies.”
They rarely stay permanently in the gut.
Is any fermentable fibre a prebiotic?
No. There are just a few fibres that are scientifically proven prebiotics: chicory root fibre (inulin, oligofructose (FOS)) and galactooligosaccharides (GOS) – the list is indeed short. There are also potential candidates that, at this point in time, lack in particular evidence related to the health benefit based on human intervention studies. The consensus statement of the International Scientific Association for Probiotics and Prebiotics (ISAPP) provides a good overview on the definition of prebiotics. [6] Many fully or partially fermentable fibres do not show a prebiotic effect.
What are proven prebiotics versus potential candidates?
The only proven prebiotics are inulin and oligofructose (synonym: fructo-oligosaccharides (FOS)) and galactooligosaccharides (GOS). As GOS is synthesised, the chicory root fibres inulin and oligofructose are the only prebiotics extracted from plants.
What is the scientific evidence for the prebiotic effect of chicory root fibres?
A systematic review with meta-analyses was conducted to investigate the prebiotic effect of chicory root fibre. This is the highest level of scientific evidence that summarises data from multiple randomised, controlled trials (RCTs), the gold standard for human intervention studies. Fifty RCTs conducted in infants, children and adults confirmed the selective increase in bifidobacteria, acknowledged beneficial bacteria, starting from 3 grams per day [10]. Significant improvements in bowel function were also demonstrated. These studies cover a range of food matrices, dietary and health conditions and intervention periods in populations from Europe, the Americas and Asia.
Why are chicory root fibres an important tool for healthy and prevention-oriented eating?
It has been proven by numerous high-quality human intervention studies that chicory root fibres stimulate the growth of beneficial bacteria in the gut, support normal bowel habits by higher stool frequency per week, facilitate weight management and increase bone mineral density by higher calcium absorption. In light of common public health challenges like overweight, obesity, diabetes, osteoporosis and constipation, chicory root fibres, as part of a mixed fibre intake, are an important tool to improve health and nutrition. Emerging research is looking into the effects of positively influencing systemic inflammation processes that are related to obesity and diabetes.
References
References
1. U.S. Department of Health and Human Services and U.S. Department of Agriculture. (2015) 2015–2020 Dietary Guidelines for Americans. 8th Edition. http://health.gov/dietaryguidelines/2015/guidelines
2. Nellesen D, Yee K, Chawla A et al. (2013) A systematic review of the economic and humanistic burden of illness in irritable bowel syndrome and chronic constipation. J Manag Care Pharm 19(9): 755–764. https://www.jmcp.org/doi/pdf/10.18553/jmcp.2013.19.9.755
3. Micka A, Siepelmeyer A, Holz A et al. (2017) Effect of consumption of chicory inulin on bowel function in healthy subjects with constipation: A randomized, double-blind, placebo-controlled trial. Int J Food Sci Nutr 68(1): 82–89. http://www.tandfonline.com/doi/pdf/10.1080/09637486.2016.1212819?needAccess=true&
4. EFSA Panel on Dietetic Products, Nutrition and Allergies (2015) Scientific Opinion on the substantiation of a health claim related to “native chicory inulin” and maintenance of normal defecation by increasing stool frequency pursuant to Article 13.5 of Regulation (EC) No 1924/20061. EFSA Journal 13 (1) 3951. http://onlinelibrary.wiley.com/doi/10.2903/j.efsa.2015.3951/epdf
5. Vandeputte D, Falony G, Vieira-Silva S et al. (2017) Prebiotic inulin-type fructans induce specific changes in the hu- man gut microbiota. Gut 66(11): 1968–1974. http://gut.bmj.com/content/gutjnl/66/11/1968.full.pdf
6. Gibson GR, Hutkins R, Sanders ME et al. (2017) Expert consensus document: The International Scientific Associa- tion for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nat Rev Gastroenterol Hepatol 14(8): Advanced online publication. http://www.nature.com/nrgastro/journal/vaop/ncurrent/pdf/nrgastro.2017.75.pdf
7. Gibson GR, Roberfroid MB (2009) Handbook of Prebiotics. CRC Press.
https://www.crcpress.com/Handbook-of-Prebiotics/Gibson-Roberfroid/p/book/9780849381713
8. The International Scientific Association for Probiotics and Prebiotics (ISAPP). Prebiotic definition updated by ISAPP (2017). https://isappscience.org/prebiotic-definition-updated-isapp/
9. The International Scientific Association for Probiotics and Prebiotics (ISAPP). Infographics. https://isappscience.org/infographics/
10. Nagy DU, Sándor-Bajusz KA, Bódy B et al. (2022) Effect of chicory-derived inulin-type fructans on abundance of Bifidobacterium and on bowel function: a systematic review with meta-analyses. Crit Rev Food Sci Nutr:1–18. https://www.tandfonline.com/doi/pdf/10.1080/10408398.2022.2098246?needAccess=true