Dietary fiber

Dietary fiber is largely indigestible food components, mainly polysaccharides, ie carbohydrates, which occur primarily in plant foods. They can be found among others in cereals, fruits, vegetables, legumes, and in small amounts in milk. For simplicity, we divide the length of fiber in water-soluble ( such as locust bean gum, guar, pectin and dextrin) and water-insoluble (for example, cellulose). Dietary fiber are now, quite unlike its name suggests, an important component of human nutrition. Not all fiber lead to the same degree to flatulence.

  • 2.1 fiber contents of various foods
  • 3.1 Reason for indigestion
  • 3.2 stomach
  • 3.3 intestine
  • 4.1 cholesterol 4.1.1 Coronary Artery Disease
  • 4.1.2 cholelithiasis ( gallstones )


The value specified in the Nährwertetabelle fiber content of a food is subject to legal provisions. § 2 of the nutrition labeling regulations (Definitions) defines, among other things:

  • = Fiber carbohydrate polymers with three or more monomeric units, which are neither digested nor absorbed in the human small intestine and belong to the following categories: a) edible carbohydrate polymers which are naturally present in foods as consumed;
  • B ) edible carbohydrate polymers which are obtained by physical, enzymatic or chemical means from food raw material and according to generally accepted scientific evidence which have a beneficial physiological effect;
  • C ) edible synthetic carbohydrate polymers which have a beneficial physiological effect by generally accepted scientific evidence;

Demarcation crude fiber

The term crude fiber was coined more than 100 years ago in the feed analysis. Since fiber partially also have a fibrous structure, they are often mistakenly equated with them. Even in English, there are several terms as " crude fiber", " dietary fiber ", "non- nutritive carbohydrates ". The fiber content exceeding in any case the crude fiber content, which consists almost entirely of cellulose. In the literature conversion factors are given 2-6, eg fiber content × 6 = fiber content. For cereals and legumes rather the higher conversion values ​​(4-6) are in fruits and vegetables about 2-3.

Types and occurrence

Dietary fiber are found in varying amounts in different plant foods. One divides roughly into water-insoluble dietary fiber and water-soluble; because of their applicability as a thickening agent a few are designed specifically for use as a food additive produced ( Alginate as salts of alginic acid from various algae, agar also algae, xanthan gum, etc.).

Fiber contents of various foods

The fiber content of the food is very different. The following tables give a few examples. A more detailed table is given in the links. After published by the Max Rubner -Institut National Nutrition Survey II cereal products are with 41% the most important source of fiber the Germans, fruit (21% ) and vegetables ( 16%). All German flour type may be referred to as roughage source by the restrictive EU directives, since they have more than 3% fiber.

Dietary fiber can bind to water up to 100 times their own weight. It is therefore especially with separate intake of dietary fiber such as flaxseed or wheat bran is very important to drink enough liquid because the Verdauungsbrei in the intestine otherwise hardened due to lack of water and clogging favors instead counteract it. Due to the different fermentability of the respective fiber these also have different calorific values ​​between 4 kcal / g and 0 kcal / g

Properties and effects

Reason for indigestion

The reason for the total or partial indigestion is either a lack of the enzyme for the cleavage of this bond, or a lack of a transport protein for the active transport through the cell wall of the gut into the intestinal mucosa. Humans, for example, has enzymes to cleave Glycosidic bonds of type α -1 → 2 (sucrose) or α -1 → 4 (eg maltose), but none for connections to the β -1 → 4- type ( cellulose). Likewise, the man has a whole range of glucose transporters. Isomalt is available in the case of a bond that can be cleaved; glucose, accounting for 50 %, is absorbed through the intestinal wall and metabolized in the body cells, the sorbitol and mannitol ( each 25 % share), however, can not be absorbed through the intestinal wall.


Fiber in the diet enlarge merely by their presence the food volume without increasing the energy content. Some fibers also have the capacity to bind large amounts of water, which means that they, if they have not already located in front of the food intake in water, swell in the stomach. The resulting increase in volume results in a greater expansion of the stomach bag, which in turn leads to a reduction of ghrelin resulting in a directly increased satiety.

Fiber effect on the gastric residence by extending this. The swelling takes time and requires either that water is drunk, or that the stomach secretes more fluid, because the chyme must have a certain minimum viscosity.


The existing fiber in the chyme ensure, through their ability to bind water, for a steady increase in its volume; Thus, fiber-rich chyme exerts additional pressure on the bowel wall and thereby stimulates peristalsis to, shortening the time spent fiber-rich foods in the intestine.

No higher animal has enzymes to water-insoluble dietary fiber (especially cellulose) to split ( in ruminants the enzymatic cleavage of these substances by microorganisms takes place, which are in their rumen ). Neither the small nor the large intestine to find such bacteria. Water-insoluble dietary fibers pass through the gastrointestinal tract thus unchanged.

A portion of the water-soluble dietary fibers, however, fermented in the colon by the intestinal flora to the portion. In this fermentation produce different amounts of partly odorless gases, such as Carbon dioxide, methane and hydrogen. There are also formed short chain carboxylic acids, such as acetate, propionate and butyrate which are largely absorbed from the colon mucosa, and contribute to nutrition of the mucous membrane cells. Short-chain fatty acids ( SCFA engl. (short chain fatty acids) ) have, compared to medium and long chain fatty acids peculiarities (see fat digestion ).

In addition to water bind dietary fiber and minerals, toxins, bile acids, and microorganisms per se. These are consequently excreted together on the chair. With a balanced mixed diet, that's not a problem for separate fiber intake may cause long but a mineral deficiency.

Some fibers are plant substances to repel from an ecological point of view predators. From poorly digested fiber fermentation toxic alcohols and biogenic amines could arise that damage the intestinal mucosa and the immune system.

Nutritional assessment

The idea that a high-fiber diet is beneficial to health, and to prevent against diseases of civilization, was triggered inter alia by an epidemiological study of Burkitt and Trowell from the 1970s that suggested that Africans who eat high fiber, significantly lower rates of some diseases of civilization cancer than Europeans and Americans under low fiber diet due to methodological shortcomings, this study is now, however, no more than a proof of that time derived from " fiber hypothesis ".

Since that time, carried out control studies could support the hypothesis in part, partly, there are still conflicting results.


A high-fiber diet may have a cholesterol-lowering effect.

The chair is the only way the human body excrete cholesterol. Fiber increase bile acid excretion in the faeces by biliary acids or salts of these bind and prevent their Rückresorbtion in the ileum. This in turn leads to a compensatory increase in bile acid synthesis that are consumed cholesterol.

There are also studies that do not confirm a cholesterol- lowering effect.

Coronary heart disease

Several studies have shown that a high-fiber diet the risk of developing coronary heart disease, and thus the risk of suffering a heart attack is reduced.

A possible mechanism for this could be the cholesterol-lowering effect of dietary fiber.

Cholelithiasis ( gallstones )

There is evidence that a high fiber diet the risk of getting cholesterol-containing gallstones, reduced. This circumstance could be generally attributed to the increase in bile acid excretion in the stool.

Blood sugar levels

Dietary fiber reduce the glycemic load of the chyme.

From fiber-rich food, the carbohydrates in the intestine are absorbed more slowly and so there is a slower, less steep rise in blood sugar after eating and to a less steep drop in blood sugar after the cleavage of the starch. Therefore, diabetics are advised to eat high fiber.

Dental caries

A fiber-rich diet stimulates for extensive chewing. She massages and strengthens the gums and cleans mechanical parts of the tooth surface. Ample chewing also increases the amount of saliva. Saliva acts as a pH buffer and the calcium phosphate contained in the saliva provides for remineralization of tooth enamel.

Diverticulosis / diverticulitis

What is certain is that a low-fiber diet promotes the occurrence of diverticulosis and its inflammatory form of diverticulitis and diverticular disease that can be treated by high-fiber foods. This could be shown that a high pressure inside the colon was found in diverticular disease patients, which could be significantly reduced by long-term treatment with wheat bran versus placebo. This high pressure is in addition to other factors for the development of colonic diverticulum ( protuberances ) blamed.

Colon Cancer

It can be assumed that the individual risk of cancer of the genetic predisposition of the existing load of food with carcinogens, the food composition, and in addition dependent on the diet is. It is still controversial how much individual factors increase or reduce the risk. There is, for example, suggested that the acceleration of intestinal transit leads through fiber diet that chyme in more or less abundant carcinogens only briefly acting on the intestinal wall, and that this will reduce the risk of cancer.

Experiments in vitro show that the butyrate formed during the fermentation of fiber (see above) prevents an impaired cell proliferation, and thus inhibit the development of cancer. However, these findings can not be readily transferred to the in vivo environment in the human intestine.

Biopsies show that around 90 percent of all colon cancers develop from either colon polyps or adenomas. However, prevention of polyps or adenomas by a high-fiber diet has not been proven by a study. Similarly, no studies known to the inferior, that a fiber-rich diet reduce the risk of degeneration of benign to malignant tumors and a high-fiber diets increase this.

The study location is uneven: A meta-analysis of five intervention studies showed no protective effect against colon cancer. In contrast, occupies the EPIC study that a high-fiber diet reduces the risk of colon cancer by about 40 percent. The reason for this discrepancy may lie in the different study designs. Thus, the EPIC study, for example, can Not rule out confounding factors.

Current recommendations

The German Nutrition Society ( DGE) recommends that you take daily for at least 30 grams of fiber to them, preferably whole grain products, vegetables, fresh or dried fruit and nuts. In a simultaneous adequate fluid intake should be maintained. The National Nutrition Survey II, however, found that 68 % of men and 75% of women take significantly less fiber to itself.

Therefore, the Association for Independent Health counseling ( UGB) recommends dietary fiber intake to increase slowly. This can be an increased consumption of vegetables cooked al dente and later carried out a slow import of raw food. Even white flour can be gradually replaced by wholemeal flour. A high fiber intake is achieved through whole food nutrition.

The Food Drink Europe ( FDE) recommend in their Guideline Daily Amounts 25 grams per day.

The Harvard School of Public Health recommends a daily intake of at least 20 grams, preferably in the form of whole grains, fruits, vegetables, legumes and nuts.

The American Heart Association recommends 25 grams daily.