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The role of dietary fiber in the digestive process
Last reviewed: 06.07.2025

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Rough "food" is precisely plant dietary fiber. These fibers can be of both carbohydrate and non-carbohydrate nature. The first group includes cellulose (or fiber) and hemicellulose, and the second group includes pectin and lignin.
What are dietary fibers made of?
All dietary fibers are natural polymers, i.e. they consist of a chain of identical substances and compounds. For example, a link in the cellulose chain is the well-known glucose. In the hemicellulose chain, the links are xylose and galactose, also sugars. Pectin, for example, is formed from galacturonic acid, and from phenylpropane (a natural polymer obtained from tree bark) it is part of lignin.
Various dietary fibers can be found in biologically active substances of the body - vitamins, mineral compounds and some other components of the body.
How does dietary fiber affect the body?
When dietary fiber enters the body, it is slightly processed and slightly destroyed by the intestinal microflora. According to research results, only 38% of cellulose, 35% of lignin and 56% of hemicellulose are digested and absorbed by the body. How well a product is digested depends not only on the chemical properties of the product, but also on the degree of its grinding. If you eat coarsely ground bran, it is absorbed much worse than finely ground bran. Even despite the grinding, dietary fiber cannot bring too much energy to the body. Thus, from 100 g of such a product, the body can get no more than 400 calories.
Regular consumption of foods rich in dietary fiber significantly increases the amount of feces and stimulates bowel function. Insufficient dietary fiber in foods can lead to intestinal atony and constipation. Evidence of this fact is that rural residents and vegetarians, who consume a lot of plant-based foods, have more feces than city dwellers and people who often eat meat.
Dietary fiber consumption worldwide
The consumption of plant foods by residents of developed countries has fallen by almost 90%. The development of the food industry and the introduction of technological innovations have done their job - now there is a huge number of refined products. Thus, with the improvement of milling technologies, the amount of dietary fiber in flour has sharply decreased. Even in the last century, a person consumed at least 15-20 g of dietary fiber per day, but now this number has fallen significantly: in Germany, people consume no more than 5 g, in Great Britain no more than 4-8 g, in the USA about 8-11 g, in Russia - 6-8 g of dietary fiber.
What should you eat and what shouldn't you?
It is now believed that in order for the intestines to function normally, a person should consume at least 25 g of dietary fiber. But we naturally prefer to choose already purified, with various flavor additives and seasonings, refined products than healthy natural ones - vegetables, fruits, rye bread and wholemeal bread. This causes such a common problem as constipation, because an irrational diet is clearly not beneficial.
Other properties of dietary fiber
In addition to the fact that dietary fiber prevents constipation and has a beneficial effect on the intestines, it has many more useful properties. Dietary fiber can improve metabolism in the body, due to its effect on various body systems. It cleanses the intestines and removes toxins, as it has sorption capabilities. Dietary fiber can significantly reduce the likelihood of malignant tumors in the gastrointestinal tract.
Regular consumption of whole grain plant foods can reduce the concentration of glucose, cholesterol and triglycerides in the blood, as well as reduce weight. This is why plant foods are indispensable in the diet of people suffering from diabetes, obesity, coronary heart disease, atherosclerosis and predisposition to these diseases.