How much fibre should you eat each day?

Dietary fibre is a collective term for components found in plant-based foods that are neither digested nor absorbed in the small intestine. It is not a single substance, but a group of compounds with varying chemical structures and different physical properties. The most common distinction is between water-soluble and water-insoluble fibre, but characteristics such as viscosity, fermentability and water-binding capacity are also important. From a nutritional perspective, this is of great importance, as its intake remains significantly too low in parts of the population.

1. Properties of fibre
2. What are the differences?
3. Products containing fibre

Properties of fibre

Fibre is distinctive in that it influences the properties of food at all stages of meal preparation and consumption, and subsequently throughout the digestive tract. It can bind water, swell, increase the volume of the food mass, alter its density, and affect the viscosity of intestinal contents. Some of its fractions form gels or solutions with higher viscosity in the presence of water, causing the food to remain in a more compact form for longer. Other fractions act primarily by increasing volume, raising the mass of intestinal contents and influencing the conditions under which they move through the large intestine.

The properties of fibre depend on the type of compound, the degree of product fragmentation, processing methods, and whether it occurs naturally in food or has been added to it. From a nutritional point of view, it is also important that some fibre fractions undergo fermentation in the large intestine. This means that they can be utilised by gut microorganisms, and the result of this process is the formation of, among other things, short-chain fatty acids.

What are the differences?

Not all fibre fractions ferment to the same extent. Some are fermented more easily and quickly, whilst others remain more resistant and act mainly through a physical effect related to the volume and structure of the digestive contents. This means that soluble fibre, such as beta-glucans, pectins, gums and plant mucilage, differs from insoluble fibre, which includes, amongst others, cellulose, some hemicelluloses and lignin. These differences affect how food behaves in the digestive tract, the rate at which nutrients come into contact with digestive enzymes, and the conditions in the large intestine.

Examples of fibre sources

Products containing fibre

The sources of dietary fibre are very diverse, and different food groups provide different types of fibre and different proportions of these types. The European Food Safety Authority considers 25 g of fibre per day to be an adequate amount for adults.

Wholemeal cereal products, particularly wheat and rye, are an exceptionally important source of insoluble fibre, including cellulose and some hemicelluloses. This is precisely why wholemeal bread, coarse groats and bran do not have the same fibre profile as fruit or pulses.

Oats and barley are distinguished by a higher content of beta-glucans, i.e. the soluble fraction, which, when combined with water, can increase the viscosity of the digestive contents. Legumes, such as lentils, beans, chickpeas and peas, provide a mixture of soluble and insoluble fibre.

Fruit is a good source of pectin, particularly apples, citrus fruits, currants and some berries, whilst vegetables provide a mixture of different types, the proportion of which depends on the variety, degree of ripeness and method of preparation.

Nuts, stones and seeds also contain fibre, but its effect may partly depend on the form in which they are consumed, as a product eaten whole, chopped, roasted or ground differs in terms of the availability of its components and physical properties.

Flaxseed and psyllium are known for their high content of mucilaginous substances that bind water effectively.

Interestingly, the diet also includes resistant starch, which is classified as a component with effects similar to fibre. It can be found, amongst other things, in unripe bananas, legume seeds, and in cooked and then cooled starchy foods such as potatoes, rice or pasta.

Sources:

• Carlsen, H., & Pajari, A. M. (2023). Dietary fiber - a scoping review for Nordic Nutrition Recommendations 2023. Food & nutrition research, 67, 10.29219/fnr.v67.9979. https://doi.org/10.29219/fnr.v67.9979
• Dhingra, D., Michael, M., Rajput, H., & Patil, R. T. (2012). Dietary fibre in foods: a review. Journal of food science and technology, 49(3), 255–266. https://doi.org/10.1007/s13197-011-0365-5
• Li, J., Lang, W., Han, S., Wu, X., Hao, F., Zhou, Y., Du, R., & Song, C. (2025). Insights into the Mechanisms and Functional Effects of Insoluble Dietary Fiber Modification: A Review. Foods (Basel, Switzerland), 15(1), 38. https://doi.org/10.3390/foods15010038