Traditionally, dietary fibre is defined as the portion of plant foods that is resistant to digestion by human gastrointestinal enzymes.
Dietary fibre itself has no nutritional value and does only provide a small amount of energy (~2 kcal/g) formed by bacterial fermentation of fibre in the colon. Nevertheless, fibres play an important role in the regulation of different physiological functions in the human body.
Some of these fibre compounds (cellulose, hemicellulose and lignin) are insoluble in water, and are therefore called insoluble fibres. They mainly act on the functioning of the gastrointestinal tract, facilitating the transit time of foods, normalising bowel movements, increasing stool bulk and preventing constipation.
Insoluble fibres are mainly found in whole grains (e.g. barley, wheat, millet, brown rice, oat, rye), vegetables and in the seeds and skin of fruits.
Other fibre compounds (like beta-glucan, pectin, gums and mucilages like pysillium) are water-soluble and are therefore called soluble fibres.
As soluble fibres can absorb water, they form a viscous bolus in the gut that partially delays and/or reduces the absorption of certain nutrients such as carbohydrates, fats and cholesterol. In this way, they contribute to the control of blood glucose and cholesterol levels1, 2.
Soluble fibres are mostly present in legumes, fruits and cereals such as oat and barley. Some plant foods contain both types of fibre.
Legumes such as dried beans, soybean, chickpeas, lentils, peas;
Vegetables such as artichoke, avocado, cabbage, broccoli, chicory, carrots, eggplant, beets;
Fresh fruit such as apples, pears, figs, bananas, kiwi, raspberries, orange, grapefruit, currants;
Nuts such as walnuts, hazelnuts, almonds;
Dried fruits and berries such as apricots, figs, apples, raisins, prunes, blackcurrants;
Wholegrains such as brown rice, oat, barley, wheat, whole-grain pasta and bread;
Beta-glucan is one main types of soluble fibre and is found in the bran of many common whole grains, with oat and barley containing the highest amounts.
Compared to other types of soluble fibres, beta-glucan is especially effective at achieving and maintaining healthy cholesterol levels3 (see below).
Examples of food products especially rich in beta-glucan are oat meal, oat bran and cereals, barley flakes, pearl barley.