Dietary Fibres

(roughage, bulk)

What are dietary fibres and where are they found?

Dietary fibres are components of plant foods that cannot be broken down by the digestive secretions and thus cannot be digested by human beings.

From a chemical point of view, dietary fibres include very varied substances in plants that have very different functions. Some dietary fibres (e.g. cellulose, hemicelluloses, pectin and lignin) are components of the plant's cell wall and give it its structure. Others lie within the cell, protecting them from drying out or serving as a store of nourishment for the plant. Most dietary fibres are grouped chemically with the carbohydrates. They are also termed non-convertible carbohydrates, or are known as fibrous material, plant fibres or waste products.

According to whether or not they are soluble in water, we differentiate between soluble and insoluble dietary fibres. To the latter group belong, among others, cellulose, hemicellulose and lignin, whereas pectin is a soluble dietary fibre. The majority of plant foods contain both soluble and insoluble dietary fibres in varying proportions. In fruits and vegetables we find above all cellulose and pectin, while in grains and legumes cellulose and hemicellulose predominate. The effects of soluble and insoluble dietary fibres in the body vary to some extent; therefore, our dietary fibre intake should be from the greatest variety of foods possible, so that we may benefit from all effects.

Whole-grain products, legumes, seeds and nuts, vegetables and fruits are rich in dietary fibre. Products made with white flour contain only scant amounts of dietary fibre. For example, whole-grain bread contains 8-9 g of dietary fibre per 100 g, white bread only 3 g.

There are considerable differences in the dietary fibre content of vegetables and fruits, according to the variety. Coarse vegetables such as types of cabbage or carrots (3-5 g/100 g), as well as berries and apples (2.5-4 g/100 g), are especially rich in dietary fibre, while cucumbers or melons haven't nearly such high dietary fibre contents (ca. 1 g/100 g).

The term roughage stems from the time when it was believed that these food components - being indigestible - were superfluous and thus unnecessary ballast for human beings. This view has meanwhile changed fundamentally. Today, dietary fibres top the list of health-promoting nutritional substances.


No doubt the best-known effects of dietary fibre are those it has on digestion. A dietary-fibre-rich diet ensures a regular and easy bowel movement, and this prevents constipation. Also other intestinal disorders that frequently occur as a result of chronic constipation, such as intestinal polyps or haemorrhoids, have little chance of developing with a dietary-fibre-rich diet.

Furthermore, a diet high in plant foods with much dietary fibre must be thoroughly chewed. This is good for our teeth and ensures a good level of satiation, as does the fact that dietary-fibre-rich food is very voluminous and fills the stomach well. A good level of satiation in turn keeps one from consuming too many calories and thus from putting on weight. Together with regular physical activity, a dietary-fibre-rich diet is the best way to prevent overweight.

In addition, dietary fibre helps to regulate the blood sugar level and prevents it from rising too quickly after a meal and then falling again just as quickly. Instead, the values remain stable for a longer period. Not only diabetics, but all of us benefit from this, because when the blood sugar drops quickly again after we eat we become hungry again just as quickly.

Moreover, dietary fibre contributes to lowering increased cholesterol levels in the blood and presumably also works to prevent intestinal cancer.


Based on the numerous favourable effects of dietary fibre, a healthy diet should by all means be rich in dietary fibre. We should consume approximately 30 g daily. Ideally, half of this should come from grain products, the other half from fruits, vegetables and other plant products.

Incidentally, it is much more healthy to consume dietary fibre in its natural form with many plant foods than in isolated form, such as bran or pectin supplements.