Parliamo di...FIBRE!

Let's talk about... FIBERS!

The European Food Safety Authority (EFSA) defines dietary fiber as the set of carbohydrates that cannot be digested by our intestine, therefore for which we do not have an enzymatic set suitable for their digestion, plus lignin. We can define dietary fibers as a very heterogeneous group of substances but with one characteristic in common: due to their chemical structure, they are neither digested nor absorbed by the small intestine. Among these substances we distinguish:

  • Non-starch polysaccharides such as cellulose, hemicellulose, gums, β-glucans..etc
  • Resistant oligosaccharides such as fructooligosaccharides and galactooligosaccharides resistant to enzymatic digestion;
  • Resistant starch fractions;

Dietary fibres, have neither nutritional nor energetic value (with the exception of the small share of energy coming from fatty acids obtained from the fermentation of the fiber by our intestinal microbiota) but equally represent a very important element for the regulation of various physiological functions of the body. Furthermore, the presence of fibers in foods forces them to be chewed for longer, increases the volume of ingested food which, as it becomes hydrated, also becomes more viscous, lengthens gastric emptying times and consequently gives a greater sense of satiety.

We can distinguish two large categories of dietary fiber: soluble fiber and insoluble fiber.

Soluble fiber

First of all, as the name itself suggests, this type of fiber is soluble in aqueous solutions, binds water molecules and therefore has great hydration capacity. As it hydrates, it forms increasingly larger and viscous complexes capable of reducing or slowing down the absorption of sugars and fats, thus contributing to the control of blood sugar and limiting the absorption of fats and cholesterol. In addition to this "metabolic" function, these large complexes slow down gastric emptying and improve the consistency of the stool, making it soft.

The peculiarity of this type of fiber is that although it is not directly digested and absorbed in our small intestine, once it reaches the colon it is completely fermented by the bacteria of the intestinal flora which use it as a substrate for the production of short-chain fatty acids, elements very important in preserving the physiology of intestinal cells and the bacteria themselves. For this reason it is not excreted and plays the role of prebiotic (they promote the growth, in the colon, of one or more bacterial species useful for the development of the probiotic microflora).

Among the soluble fibers we recognize hemicelluloses, β-glucans, pectins, gums, resistant starches and inulin.

Insoluble fibre

This type of fiber, however, is insoluble in aqueous solutions, is poorly fermented in the colon and is consequently almost completely excreted in the feces. Its function is "mechanical", by retaining the water and gases present in the intestinal lumen it increases fecal mass and promotes intestinal motility by increasing transit speed. This type of fiber is very important because it is able to bind toxic substances and drug residues, promoting their elimination.

Some examples of insoluble fibers are cellulose, lignin and some hemicelluloses.

Recommended intake quantities

EFSA, in the document drawn up in 2010 on dietary reference values ​​for nutrient intake, recommends the intake of 25 grams of dietary fiber per day as sufficient to guarantee normal intestinal function in adults. In accordance with this, the LARNs also set the nutritional objective of taking at least 25 g/day of dietary fiber even in the case of energy intakes <2000 kcal/day, adding the indication to prefer foods naturally rich in dietary fiber such as whole grains , legumes, fruit and vegetables.

So to summarize…

Dietary fibres, if associated with sufficient hydration, act as regulators of intestinal transit: in fact they reduce constipation (slowing down transit) and limit its acceleration (diarrhoeal episodes). Furthermore, thanks to the reduction in the speed of digestion, fibers also optimize the sense of satiety and help to control appetite more effectively.

As a substrate of the intestinal microbiota, which is an essential defense and control organ for the body, fibers contribute to the prevention of numerous pathologies (cardiovascular diseases, obesity, type 2 diabetes, some tumors) and also the risk of infections and of inflammatory pathologies, modulating the activity of the immune system.

Bibliography

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