Fiber classification

Classification of dietary fiber

We can classify dietary fiber according to different criteria, although from a functional and nutritional point of view we use the criterion of its solubility in water.

Soluble dietary fiber is characterized by undergoing a process of destruction by bacteria in the colon, with the production of hydrogen, methane, carbon dioxide and short-chain fatty acids (acetic, propionic and butyric) that can act locally and can be absorbed by the body and used as a source of energy. Although the energy is low, it should not be underestimated: each gram of ingested fiber contributes between 1 and 2.5 kcal. Obviously, the energy value of the fiber will depend on its degree of fermentability ("destruction") by the bacteria in the colon: the higher the fermentability, the higher the energy.

Soluble fiber is hydrolyzed or completely destroyed by bacteria. It has the following properties, which will explain its effects on health and disease: it is very viscous (like a gel), slows intestinal emptying, slows the absorption of nutrients, improves glucose tolerance (by reducing sugar spikes in blood), lowers cholesterol levels and slightly increases fecal bolus. For all this, it has an antidiarrheal effect, favors the growth and integrity of the cells of the intestine and colon wall, and helps lower cholesterol and blood sugar.

Soluble fiber includes hydrolysis resistant starches, pectins, gums and mucilages, some hemicelluloses, and indigestible oligosaccharides (inulin and oligofructose).

A particular variety of soluble fiber is psyllium, obtained from the bark of a bush and used as a laxative (by increasing the fecal bolus) and formerly as a cholesterol-lowering agent in patients with moderate hypercholesterolemia.

Insoluble fiber hardly undergoes fermentation or hydrolysis processes by bacteria in the colon. It has the following properties, which will explain its effects on health and disease: it is not very viscous (they do not form a gel), it favors the uptake of water, increases the fecal bolus, increases bowel movement and accelerates intestinal transit. With all this improves constipation.

The use of large amounts of insoluble fiber can be associated with calcium and iron deficiencies.

Insoluble fiber includes cellulose, lignin, and some hemicelluloses.

Sources of dietary fiber

All plant products contain both types of fiber. Most contain a mixture of soluble and insoluble fiber in a ratio of about 1: 3. Soluble fiber predominates in fruits (pulp), vegetables, greens, and legumes. Insoluble fiber in cereals, greens, vegetables and legumes.

In short, the main sources of dietary fiber in our diet are vegetables, cereals, fruits and legumes, all of which are considered typical of the Mediterranean diet. It is not surprising, then, that our diet is rich in fiber and other substances considered beneficial for health.

Fiber-free foods are:

• Milk and derivatives
• Eggs <
• meats
• Simple sugar (table sugar, honey sugar, etc.)
• Fats
• Seasonings