Dietary Fibrs – Classification and functions

Certain types of carbohydrates are classified as dietary fibres. In general, these fibress are indigestible polysaccharides (complex carbs), but other organic compounds are considered as fibres as well. Usually plant-based foods, such as grains, legumes, and vegetables deliver the vast majority of fibers in our daily diet. That is because these indigestible polysaccharides serve the plants in several ways. For example they are involved in building the cell’s structural framework and they provide cellular protection (Schusdziarra et al., 2011). 

Principally dietary fibres can neither be absorbed themselves in the digestive tract, in particular in the small intestine, nor are enzymes able to reduce them to smaller digestible pieces. Thus, they get undigested into the colon. Hence, fibers don’t play a major role when it comes to energy supply. Nevertheless, on their way through the alimentary canal fibers can unfold a variety of effects and thus can positively impact the metabolism of the whole body. The following article covers, inter alia, how dietary fibres can be categorized and how several parts of the digestive system are influenced by these undigestible sugars (Biesalski et al., 2017). Download a PDF of this article for FREE. You will find the link below the post.


Dietary fibres - spoon full of chia seeds - Picture by ValeriaLu from Pixabay
Dietary fibres – spoon full of chia seeds – Picture by ValeriaLu from Pixabay

Fibres – Classification

Because of distinct properties fibers can be categorized in different classes. For this purpose the solubility of fibers is often considered. However, others properties, such as the structure or the fermentability, could be considered as well (Ströhle et al., 2012). When it comes to the solubility fibers can be distinguished in the following classes:

Soluble fibres

As their name suggests soluble fibers dissolve in water. This means, that this type of fiber can absorb much fluid (< 60 ml/g) and swell up as a result. Imagine you eat something that contains some fibers. You take a bite and after chewing for a while a piece slides down your oesophagus and lands in your stomach. Then the gastric acid dissolves the bolus and the soluble fibers within will dissolve in the fluid to form a jellylike structure. And, because of this jellylike structure the bolus will move with a comparatively slow velocity just little by little from the stomach into the small intestine. Most fruits and vegetables contain larger quantities of soluble fibers, especially pectin (Ströhle et al., 2012).

Insoluble fibres

Compared to their soluble counterparts insoluble fibers can absorb considerably less water (about 3 ml/g), which results in an obviously limited swellability. Roughage is primarily contained in whole grain products and legumes (Ströhle et al., 2012).

The follwoing table displays some soluble and insoluble fibers (Schusdziarra et al., 2011).

Tab. 1: The table shows some members of soluble and insoluble fibers.

Soluble fibres

Insoluble fibres






Some hemicelluloses

Some hemicelluloses


Fibres – Effects

Fibers can have an influence on several organs of the digestive tract. The overview below will look at different stages of the alimentary canal regarding the effects that dietary fibers can have (The following stages are considered on the understanding that the food was rich in fibers.).


Effects of dietary fibres in the mouth

If you compare the consumption of fiber-rich food, such as eating a whole-grain roll, with the consumption of white bread, which is relatively low in fibers, then you will probably agree, that the whole-grain roll needs to be more chewed to make it smaller in size. This implies that fibers necessitate intensive and prolonged chewing. If chewing took longer, ingestion would take longer, too. And, as a consequence there is a chance satiation sets in before the plate is empty. Thus, fibers can contribte to satiation. But besides that, because of prolonged chewing saliva release is stimulated. Since, saliva contains, inter alia, antibacterial substances, increased salivation may help to neutralise unwanted bacteria and therefore contribute to dental health (Ströhle et al., 2012).


Effects of dietary fibres in the stomach

Dietary fiber effect in the stomach As mentioned above, certain dietary fibers can swell when combined with water. Extensive chewing causes the moistened food pulp, which is actually already mixed with liquid, to slide down the esophagus and end up in the stomach. There the chyme is mixed with the gastric acid by circulation processes. The dietary fibers have had and continue to have plenty of time to swell. The more the dietary fiber swells, the greater the volume and viscosity of the porridge. You may already notice how your stomach is filling up (for a self-experiment: mix 100 – 150 g of oatmeal with a little water. Then eat it as muesli and drink 1 – 2 glasses of water. Now it’s time to wait.). More volume and more viscosity of the chyme lead to slower emptying of the stomach and consequently to increased satiety (Ströhle et al., 2012).


Effects of dietary fibres in the small intestine

The chyme now gradually moves from the stomach into the small intestine. The small intestine is the main place where nutrients are received. H. something like simple sugars or amino acids z. B. from here to the liver. If the food pulp is not passed on so quickly, but rather gradually, from the stomach to the small intestine, the nutrients also “only” gradually migrate to the liver. That can’t be so bad, because e.g. B. the blood sugar level and thus the insulin level rises rather slowly and can be kept constant, compared to a rapid rise in blood sugar levels after eating quickly digestible foods such as white bread (Ströhle et al., 2012).

Effects of dietary fibres in the colon

The large intestine is populated with bacteria that are very important for intestinal health. Dietary fibers can significantly limit the proliferation of undesirable microorganisms (Ströhle et al., 2012) by e.g. ensure that the “good” bacteria present (Bifidus and Lactobacillus) multiply (Biesalski et al., 2017). The soluble dietary fibers in particular can ensure that the microbial cell mass increases. The water-insoluble fiber can increase stool volume (Ströhle et al., 2012). Increased stool volume can promote defecation (Biesalski et al., 2017).


Other effects of dietary fibres

Dietary fiber can help eliminate cholesterol and thus hinder the formation of cholesterol-containing gallstones by promoting the production of bile acid (Biesalski et al., 2017). The chyme is transported more quickly in the small and large intestine due to the presence of roughage. One speaks of a shortened transit time (transit time) due to increased peristalsis (movement of hollow organs to move the contents). Dietary fiber can help prevent cancer in the colon and rectum (Biesalski et al., 2017).


Fibre-rich foods

Tab. 2: Various high-fiber foods are listed (Ströhle et al., 2012).


Dietary fibres per 100 g











Wheat flour, type 405




Wheat, whole grain


Peas, seeds, dry


Lentils, seeds, dry





Biesalski, H. K., Pirlich, M., Bischoff, S. C., & Weimann, A. (Eds.). (2017). Ernährungsmedizin: Nach dem Curriculum Ernährungsmedizin der Bundesärztekammer. Georg Thieme Verlag.

Schusdziarra, V., Hausmann, M., Sassen, M., Kellner, M., Mittermeier, J. & Erdmann, J. (2011). Ballaststoffe, Energieaufnahme und Lebensmittelverzehr. Aktuelle Ernährungsmedizin. Vol. 36. Issue 1. pp. 23-30.

Ströhle, A., Wolters, M. & Hahn, A. (2012). Gesundheitliche Aspekte von Ballaststoffen – Ein Update, Teil 1: Von der Struktur zur Funktion. Deutsche Apotheker Zeitung. Nr. 31.




My newsletter comes once a month and shows you a selection of articles that have recently been published. Since, I can't publish with a certain regularity, that's a great thing, isn't it!?😉

Information on the registration process, service provider, statistical evaluation and revocation can be found in my Data protection

In order to make my newsletter interesting for you, I statistically record which links the users have clicked in the newsletter. By registering, you agree to this statistical recording.

Be the first to comment

Leave a Reply

Your email address will not be published.