What are dietary fiber and why is it needed
Non-digestible carbohydrates also enter the human body with plant foods. All of them are polymers of monosaccharides and their derivatives. Indigestible carbohydrates can be divided into “coarse” and “soft” dietary fiber.
Fiber-rich foods: healthy dietary fiber
Of the “coarse” dietary fiber, fiber (cellulose) is most often present in food. It, like starch, is a glucose polymer, however, due to differences in the structure of the molecular chain, cellulose is not degraded in the human intestine.
Some representatives of hemicelluloses also belong to the group of coarse dietary fiber. They consist of a variety of five-membered – pentoses (xylose, arabinose) and six-membered – hexoses (fructose, galactose) carbohydrates. The representative of coarse dietary fiber is lignin, the second component of wood after cellulose. However, according to its chemical structure, lignin is not a carbohydrate, but a polymer of aromatic alcohols. Indigestible carbohydrates also include phytic acid, a substance similar in structure to cellulose. Phytin is found in plant seeds. It is similar in structure to cellulose and chitin is a polysaccharide that makes up the cell walls of fungi and shells of crayfish, crabs and other arthropods.
The “soft” dietary fiber includes pectins, gums, dextrans, agarose.
“Coarse” and “soft” dietary fiber are not energy sources. In humans, they can only partially be broken down in the colon by the action of microorganisms. Thus, cellulose is broken down by 30-40%, hemicellulose – by 60-80%, pectin substances – by 95%. Bacteria use almost all of the energy released during this process for their own needs. Most of the monosaccharides formed during the breakdown of dietary fiber are converted into volatile fatty acids (propionic, butyric, and acetic). They can be partially absorbed through the intestinal wall, but only about 1% of the nutrients formed during the breakdown of dietary fiber enter the human body. In energy metabolism, this fraction is negligible and is usually neglected. Lignin, which is quite abundant in the cell walls of plant products,
Functions of dietary fiber
Dietary fiber is traditionally called “ballast substances”, although it has long been known that they play an important role in the digestion processes and in the life of the body as a whole.
The functions of dietary fiber are varied. They reduce the rate of absorption of mono- and disaccharides in the intestine and thereby protect the body from increased blood glucose and increased insulin synthesis, which stimulates the synthesis of fats. This does not exhaust the participation of dietary fiber in lipid metabolism.
Dietary fiber increases the binding and excretion of bile acids, neutral steroids, including cholesterol from the body, and reduces the absorption of cholesterol and fats in the small intestine. They reduce the synthesis of cholesterol, lipoproteins and fatty acids in the liver, accelerate the synthesis of lipase in the adipose tissue – an enzyme under the influence of which the breakdown of fat occurs, that is, it has a positive effect on fat metabolism. Thus, dietary fiber to some extent prevents deviation from the ideal mass. They lower cholesterol and phospholipid levels in bile by preventing gallstones from falling out. The effect on cholesterol metabolism in pectins, in particular, apple and citrus, is especially pronounced.
Ballast substances make up about a third of feces, provide normal intestinal motility, biliary tract, prevent the development of constipation, hemorrhoids, colon cancer. If the diet lacks fiber, then food passes through the gastrointestinal tract slowly, feces accumulate in the colon. Even Hippocrates recommended the use of cereal bran to combat constipation. Dietary fiber binds from 8 to 50% of nitrosamines and other heterocyclic compounds with carcinogenic activity. These substances are formed when frying meat, and are also an indispensable participant in the digestion process, as they are formed during the breakdown of bile enzymes in the intestine. Long-term retention of feces in the colon causes the accumulation and absorption of carcinogenic compounds,
In addition, dietary fiber is a substrate on which bacteria of the intestinal microflora develop, and pectins are also one of the nutrients for these bacteria. The sorbing properties of pectins are also important – the ability to bind and remove cholesterol, radionuclides, heavy metals (lead, mercury, strontium, cadmium, etc.) and carcinogenic substances from the body. Pectins promote the healing of the intestinal mucosa if it is damaged. The normal intestinal microflora includes several hundred species of bacteria. Some of them assimilate nutrients through biochemical processes of decay and fermentation. Pectins suppress the vital activity of these microorganisms, which contributes to the normalization of the composition of the intestinal microflora.
All this is the basis for the use of dietary fiber in the prevention and treatment of obesity, atherosclerosis, coronary heart disease, hypertension, cancer, diseases of the digestive system.
Dietary fiber: effect on the body
The mechanism of action of dietary fiber in the treatment and prevention of obesity is based on the fact that, with their sufficient intake with food:
- the rate of gastric emptying decreases;
- its stretching increases, which helps suppress appetite, creates a feeling of fullness, preventing overeating;
- replacement of more energy-intensive foods in the diet with dietary fiber helps to reduce the intake of energy from food;
- due to the effect on the metabolism of carbohydrates and fats, dietary fibers reduce fat synthesis in adipose tissue;
- dietary fiber is a source of potassium and has a diuretic effect, that is, it promotes the excretion of water and sodium from the body.
This makes it possible to recommend the use of dietary fiber as a body weight regulator.
Fiber content of the edible portion of some foods
Very large (2.5% or more) : wheat bran, beans, oatmeal, nuts, dates, strawberries, currants, raspberries, figs, blueberries, cranberries, mountain ash, gooseberries, prunes, apricots, raisins. The foods on this list are those with the most fiber.
Large (1-2%): buckwheat, pearl barley, barley, oat flakes “Hercules”, shelled peas, potatoes, carrots, white cabbage, green peas, eggplants, bell peppers, pumpkin, sorrel, quince, oranges, lemons, lingonberries , fresh mushrooms.
Moderate (0.6-0.9%): seeded rye bread, millet, corn grits, onions, cucumbers, beets, tomatoes, radishes, cauliflower, melons, apricots, pears, peaches, apples, grapes, bananas, tangerines.
Small (0.3-0.5%): wheat bread made of 2nd grade flour, rice, wheat groats, kayaks, lettuce, watermelons, cherries, plums, sweet cherries.
Very small: wheat bread made from flour of the 1st and highest grade, semolina, pasta, biscuits.
Carbohydrates in foods with a low fiber content are called “unprotected”, with high – “protected”, as fiber slows down the access of digestive enzymes to carbohydrates. They begin to be absorbed only after the intestinal microorganisms have partially destroyed the cell membranes.
Fiber content of some foods
“Coarse” dietary fiber is found in a variety of foods. Most of them are found in wholemeal flour, millet, beans, peas, dried fruits, beets.
In many berries (for example, raspberries, strawberries, gooseberries, strawberries), most of the fiber is found in the grains. A lot of fiber in dried fruits – apricots, raisins, prunes. Many ballast substances are found in cereals and legumes.
Pectin substances in noticeable quantities are found mainly in products from which jelly can be cooked. These are plums, black currants, apples and other fruits. They contain about 1% pectin. The same amount of pectin is present in beets.
The daily diet should contain 20-60 g of dietary fiber. About half of this amount is recommended to be obtained from fiber (cellulose and hemicellulose). If the diet contains an insufficient amount of healthy dietary fiber, it is recommended to supplement it with wheat or rye bran and preparations containing pectin and cellulose in the form of microcrystalline cellulose (MCC) or methylcellulose.
Bran and pectin preparations can be taken not only in “pure form”, but also added to food. Preparations based on apple and beet pectin are produced in the form of a powder, which contains 16-25% pure pectin. In water, they swell and form a jelly-like mass, and they can be used to make drinks similar to jelly. Pectins are used in the production of marmalade, marshmallow and marshmallow (in simpler varieties – fruit pectins, in expensive ones – agarose from seaweed). These sweets are recommended for dietary nutrition, are useful for children, especially since their soft consistency, unlike caramel, protects teeth from damage. Confectionery products based on pectin do not contain fat, therefore, when overweight, marmalade and marshmallows are less “dangerous” than chocolate and other sweets with a high fat content.
Until recently, there was a trend in the food industry towards the production of refined and de-ballasted products. This became one of the reasons for the growth of “diseases of civilization” – obesity, atherosclerosis, diabetes, coronary heart disease, saline arthrosis and a number of others.
In recent decades, a fascination with dietary fiber has spread and the use of so-called rough foods in the diet: rye bread, legumes, vegetables and fruits. The consumption of baked goods and other foods with dietary fiber supplements is welcome. But an excessive enthusiasm for microcrystalline cellulose and methylcellulose, as well as bran, which many add to food in clearly overestimated quantities, is also not indifferent to the body. Ballast substances have high sorbing properties, and their excessive consumption can lead to the development of vitamin deficiency, anemia due to the excretion of iron, to a deficiency of calcium and other macro- and microelements, Deficiency of vitamins and inorganic elements in the diet can adversely affect metabolic processes and, Consequently.