Functions of dietary fiber
Sources in food
Dietary fiber or dietary fibre (alternate names: roughage, bulk, diet-fiber) is a complex of substances of cell walls of plants which are not digested and not absorbed in a human's digestive tract. It is a mixture of substances of polysaccharide character (cellulose, hemicelluloses, pectins, gums, mucilages) and not-polysaccharide one (lignins).
Functions of dietary fiber
1. It helps in constipation, diverticulosis, diarrhea and aches assisting hemorrhoids, prevents colon cancer and rectal cancer.
Dietary fiber travels through the whole digestive tract in practically unchanged state. However along the whole route it absorbs water, by what it increases the volume of feces mass and accelerates elimination of undigested leftovers. It makes regular defecation easier. Food containing much dietary fiber helps to prevent constipation and aches assisting hemorrhoids because it increases the water content in feces by what it is easier to expel it from organism.
2. It helps in fight against obesity, in weight loss and weight reduction.
Dietary fiber helps to get rid of redundant kilograms because it absorbs water, by what it expans and fulfills stomach decreasing hunger and also delaying the moment in which food leaves stomach.
3. It decreases level of cholesterol and triglycerides.
Soluble dietary fiber (pectins) is decomposed to tricarboxylic fatty acids which are responsible for inhibition of cholesterol biosynthesis in liver. Thanks its consistency it catches and removes gall acids from intestines. Because liver uses them to cholesterol production, the cholesterol level drops down when they have been expelled. Expelling of gall acids is a main way of cholesterol excess removing by organism, because it cannot be metabolized as other fats. Insoluble dietary fiber decreases level of triglycerides in blood by what it reduces the hazard of arteriosclerosis.
4. It stabilizes glucose concentration in blood.
Dietary fiber postpones carbohydrate transformation by partial blocking of access of glucose to blood, what next increases insulin secretion and helps in keeping stable sugar level in blood. Additionally insulin secretion is partially activated and regulated by hormonal system (stomach peptide inhibiting GIP and enteroglucagon). Increment of dietary fiber consumption leads to decrease of hormone level.
5. It purifies organism from toxins and heavy metals.
Soluble and insoluble dietary fiber helps to eliminate from organism toxins, gall acids, heavy metals (thanks ionoexchanging abilities of free carboxylic groups) and even carcinogenic substances (e.g. level of nitrites in organism is efficiently decreased by pectins found in apple, currants and other fruit if they have not been excessively sprayed).
Primary classification of dietary fiber includes the following fractions:
|Dietary fiber fraction name||Water solubility||Main sources||Role in nutrition|
|Cellulose||Insoluble||Vegetables, fruit, cereal grains||They help prevent and remove constipation, diverticulosis, stabilizes glucose level in blood, limits body mass increment, prevents formation of colon cancer and rectal cancer, bonds water and increases the amounts of expelled waste, helps in washing out of toxins and by-products of metabolism in digestive tract.|
|Hemicellulose||Partly soluble||Cereal grains, bran||They decrease body mass increment and lower cholesterol level, prevent formation of colon cancer and rectal cancer.|
|Lignins||Insoluble||Cereal grains, "lignified" vegetables||They remove excess of gall acids and food cholesterol, prevent and remove constipation, diverticulosis, prevent formation of gallstones and tumors of terminal parts of digestive system.|
|Pectins||Soluble||Fruit||They decrease cholesterol level in blood, regulate gall acid balance, prevent against tumors and gallstone formation.|
|Gums and mucilages||Soluble||Food additives||They decrease cholesterol and glucose level in blood, cause occurrence of feeling of satiety.|
Sources in food
Wide discrepancy in given by different authors content of dietary fiber in the same products are caused not only by plant material variation, but also by use of different determination methods.
Some people don't tolerate fibrous foods well. If you can't consume enough fiber in your diet alone, certain stool softening and bulking agents are available. These products absorb water and produce the bulk necessary for the digestive tract to perform naturally. They help create a soft and well-formed stool.
Products of animal origin (meat and natural preserves, fish, milk and natural preserves, eggs) and also alcohol, butter, oils and other fat products do not contain dietary fiber.
Table provides content of dietary fiber for 100 [g] or 100 [ml] of food.
100 grams [g] = 0,22 pound [lb] = 3,53 ounces [oz]
|Product||Content in 100 [g]|
|Black currant juice||0,1|
|Carrot with apple and orange juice||1,9|
|Carrot with apple juice||2,2|
|Carrot with orange juice||1,7|
|Muesli with fruit||8|
|Muesli with raisins and nuts||9,7|
|Soybean (soya bean)||15,7|
|Fruit jam low sweetened||0,8|
|Fruit jam high sweetened||0,9|
|Groats and rice|
|Hulled pearl barley groats||5,4|
|Natural (brown) rice (dry)||8,7|
|Pearl barley groats||6,2|
|White rice (dry)||2,4|
|Nuts and seeds|
|Coconuts dried (pulp)||23,5|
|Cream filled cookies||1,2|
|Kit Kat bar||1,9|
|Milk chocolate with nuts||0,4|
|Milky Way bar||0,5|
|Bamboo shoots canned||1,4|
|French fries (chips)||2,9|
|Green peas canned||5,7|
|Red pepper canned||1,8|
|String beans canned||2,4|
|Sweet corn canned||3,9|
|Vegetables and mushrooms|
In industrialized countries the average consumption of dietary fiber is about 15 grams per day (the average American only consumes 14 grams of dietary fiber per day). In not-industrialized societies, in Africa daily dietary fiber consumption amounts to 60 g. The effect of it is very low morbidity on tumor diseases of colon cancer and rectal cancer. The World Health Organization (WHO) recommends consumption (RDA) of 20-40 g of dietary fiber a day.
RDA for various life stage groups
|Life stage group||
Recommended Dietary Allowances (RDA)
|Infants 0-6 months||ND|
|Infants 6-12 months||ND
|Children 1-3 years||19
|Children 4-8 years||25
|Males 9-13 years||31
|Males 14-18 years||38
|Males 19-30 years||38
|Males 31-50 years||38
|Males 51-70 years||30
|Males > 70 years||30
|Females 9-13 years||26
|Females 14-18 years||26
|Females 19-30 years||25
|Females 31-50 years||25
|Females 51-70 years||21
|Females > 70 years||21
|Pregnancy ? 18 years||28
|Pregnancy 19-30 years||28
|Pregnancy 31-50 years||28
|Lactation ? 18 years||29
|Lactation 19-30 years||29
|Lactation 31-50 years||29
ND = Not determinable due to lack of data of adverse effects in this age group and concern with regard to lack of ability to handle excess amounts. Source of intake should be from food only to prevent high levels of intake.
High dietary fiber dose may lower efficiency of other medicines e.g. oral contraceptives and medicines decreasing cholesterol concentration. One should keep a 2-hour interval between a meal and such medicine taking.
- Swallowing of big quantity of pills or capsules containing dietary fiber may be dangerous. After too low water saturation they increase their volume and may stick in throat or intestines.
- Dietary fiber may restrict absorption of nutrients such as iron, magnesium, phosphorus, zinc and calcium. Fiber users are advised to avoid taking supplements at the same time as, or soon before or after, taking vitamin or mineral supplements.
- Dietary fiber in large intestine (colon) absorbs water. If there is not enough water stool will be hard and dense, it may also cause constipation. To minimize fiber effects and optimize elimination of by-products of metabolism at least 2 liters of water ought to be provided.
- Sudden organism providing with high dose of dietary fiber may cause flatulence and belly aches. It concerns especially pod vegetables. In some people products containing much dietary fiber, especially wheat ones, may irritate stomach.