Dietary fibre: role and function

Data from a national study by the German Federal Ministry of Food reveal:
75% of women and 68% of men in Germany do not eat enough dietary fibre. The possible reason: most people do not even know how important dietary fibres actually are. Dietary fibres are food components that cannot be digested and are excreted almost unchanged. For the human body, however, they are anything but ballast. They are believed to have a preventive effect against obesity, elevated blood fat levels, high blood pressure and coronary heart disease (CHD). Yet we consume less than the recommended daily amount of these beneficial helpers. Find out here how valuable dietary fibres are for our health and what you need to bear in mind when eating dietary fibres.

For simple everyday tips and exciting facts, go straight to the bottom!

Water-insoluble and water-soluble dietary fibres — what is the difference?

The substances found in mostly plant-based foods are simply carbohydrates that can be simplified into water-soluble or non-water-soluble dietary fibres. Water-insoluble dietary fibres and fibrous substances such as cellulose (main component of plant cells) or lignin (plant support material) hardly change their structure in the intestine and are excreted undigested. They are mainly found in the bran (remains of the grain husks) of different types of grain such as wheat, oats, barley, but also soy. They are also found in the outer layers of fruit, vegetables and seeds or nuts. Insoluble dietary fibres can swell only slightly in combination with water, but still contribute to increasing stool volume and stimulating intestinal peristalsis (intestinal movement). These substances also benefit the intestinal microbiome, as they lower the pH value of the intestinal milieu and thus promote the growth of “good” intestinal bacteria. They are particularly beneficial in the treatment of constipation and in connection with irritable bowel syndrome.

Water-soluble dietary fibres are, for example, pectin and inulin, which are found in most types of fruit, but also in oats, barley or legumes. They attract water and thus swell, which is why they are also called swelling agents. They also increase the volume of the intestine and thus increase its movements. In addition, these substances can be partially converted into gases and fatty acids in the large intestine by the resident bacteria of the intestinal flora. This is also called fermentation. This process is associated with the regulation of blood sugar levels, the reduction of inflammation and the reduction of the risk of heart attack or diabetes.

Fibre also includes resistant starch and oligosaccharides, which we have already reported on in the article on complex carbohydrates. The so-called resistant starch from rice, pulses and potatoes cannot be broken down and digested by human digestive enzymes and is similar in function to water-soluble dietary fibres. Oligosaccharides are carbohydrates that consist of several compound simple sugar molecules. Bifido and lactic acid bacteria of the intestinal flora are promoted by them. As prebiotics, these dietary fibres have a positive influence on the bacterial composition of our digestive tract. They are found especially in plants such as beets, chicory, garlic, asparagus, onions or soybeans.

What functions do dietary fibres fulfil in the body?

Unlike other animals such as ruminants (e.g. cattle, sheep, goats), the human intestine is not able to digest dietary fibre because it lacks a certain enzyme. However, even if or precisely because dietary fibres themselves cannot be digested, they can develop their positive effects in the intestine.

1. Dietary fibre helps to empty the intestines more quickly and to remove harmful substances from them

Dietary fibre increases the volume of food in the intestine and thus stimulates intestinal activity. The intestinal contents are transported faster and the time until digestive residues are excreted is shortened. Too slow digestion can cause the development of so-called diverticula (protrusions of the intestinal wall) and promote inflammation. The accelerated emptying of the intestines after a fibre-rich diet prevents these protrusions.

2. Dietary fibres strengthen the intestinal flora and thus the immune system.

Dietary fibres are the food for “good” bacteria in our intestines. According to studies, the composition of the intestinal flora not only positively influences our mood, but also our immune system. Water-insoluble dietary fibres ensure a stable acidic pH value in the intestine, while water-soluble dietary fibres serve as food for “good” intestinal bacteria and promote their growth. The presence of good intestinal bacteria curbs an overgrowth of “bad” intestinal bacteria and thus ensures an optimal digestive environment.

3. Dietary fibre prevents bowel cancer

In 2005, a Europe-wide study led by the International Agency for Research on Cancer showed that dietary fibre helps prevent cancer. This study examined the eating habits of over 500,000 Europeans. An intake of 30 to 35 g of dietary fibre on average reduced the risk of developing colorectal cancer by 25 % compared to those subjects who ate only 15 g of dietary fibre.

The accelerated intestinal passage triggered by dietary fibre means that cancer-causing substances in the food pulp come into contact with the intestinal mucosa for a shorter time and are excreted again more quickly. Many harmful and toxic substances such as heavy metals and pesticides can also be bound and rendered harmless by dietary fibre.

4. Dietary fibres lower the cholesterol level

Water-soluble dietary fibres from fruit, cereals and pulses bind bile acids, which are important for fat digestion. Bile acids are formed in the liver, stored in the gallbladder and released into the intestine when a high-fat diet is consumed. Bile acids are normally “recycled” to save resources. The more fibre-rich the diet, the higher the bile acid excretion via the intestine, and the more bile acids have to be replenished. In order for new bile acids to be formed, the body needs cholesterol from the bloodstream. The result: the level of harmful cholesterol (LDL) in the blood drops. The short-chain fatty acids that are produced during the processing of water-soluble dietary fibres additionally prevent the production of LDL cholesterol in the liver. The blood vessels are protected from fat deposits and do not narrow as easily — the risk of vascular diseases is significantly reduced. This was also confirmed in a study by the University of Marseille in France. The researchers analysed the dietary behaviour of more than 12,000 test persons over several years. The result: the intake of at least 30 g of dietary fibre daily reduced the risk of coronary artery disease by 34 %. The risk of heart attack was also reduced by 27 %.

5. Dietary fibres help with weight loss

Because of their high fibre content, fibre-rich foods take longer to chew. The feeling of satiety is better perceived and the portion is also perceived as larger, even if the calorie content is relatively lower.

How much dietary fibre does the body need daily?

The German Nutrition Society recommends a dietary fibre intake of at least 30 g per day. Other sources even recommend up to 40 g. However, an adequate supply of dietary fibre is not achieved by simply adding bran flakes to yoghurt. Isolated dietary fibres alone cannot replace the complex effect of high-quality food! The positive effect of dietary fibre is mainly achieved through the nutrient composition in high-fibre foods — i.e. whole fruits, vegetables and legumes. In addition, a sufficient fluid intake of at least 1.5 to 2 litres per day is necessary so that the dietary fibres can also swell up in the gastrointestinal tract and unfold their positive effect.

Foods that are particularly rich in fibre are:

• Fruit, such as apples or pears
• Vegetables, especially carrots, potatoes and cabbage
• Whole-grain products, e.g. bread and whole-grain pasta
  Pulses (beans, lentils, etc.)
• Nuts

Is dietary fibre suitable for everyone?

An insufficient intake of dietary fibre is considered to be the main cause of constipation, which affects about 30 % of all Germans. Although most people benefit from a high-fibre diet, there are some who do not tolerate a high-fibre diet well. Stomach pain, flatulence and abdominal cramps can cause many people to stop eating a high-fibre diet, especially in the early stages of a dietary change.

Simple everyday tips for a high-fibre diet:

• Prefer the wholemeal variety for bread and pasta.
• When baking, replace at least 50% of the flour in favour of wholemeal flour.
• Make your own muesli or granola (oatmeal, cereal, dried fruit, fresh fruit and nuts).
• Include three servings of vegetables and two servings of fruit in your daily diet.
• Have a handful of nuts on a regular basis.

Did you know?

• Chicory stimulates the metabolism due to the bitter substances it contains — store in a cool, dark place, wash quickly and process raw!
• Figs are considered a classic aid for constipation because of their high fibre content.
• Cucumber stimulates the activity of the intestines. Daily consumption helps with chronic constipation.
• Oats (as a whole grain) are excellent helpers for stomach and intestinal disorders because of their good swelling capacity. It is tasty in muesli or pancakes.
• Pulses (e.g. peas, lentils or soybeans) have an enormously high fibre content — cook until soft, puree and add “deflating spices”, for example cumin, ginger or coriander.
• Carrots can almost completely replace laxatives — peel little, best eaten raw and chopped or chewed well.
• Plums are considered a miracle weapon in terms of digestion — always eat raw and supplement with fats (e.g. with nuts).
• Rhubarb has a mild laxative effect due to the classic laxative substances anthraquinones.
• Rye (as a whole grain) stimulates digestive juices and promotes intestinal peristalsis.
• Sauerkraut (pickled cabbage) is ideal for constipation — do not wash, just cook gently. It is also edible as a salad.
• Wheat (as a whole grain): Its bran is an excellent source of dietary fibre. Whole wheat flour can be used in bread and pasta.
• Onions stimulate the digestive glands and build up the intestinal flora — best eaten raw!

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