Why is it essential to get plenty of fiber?

Dietary fibers are carbohydrate polymers of mainly vegetable origin. These edible carbohydrates, of very heterogeneous origin and chemical composition, cannot be digested or absorbed in the human small intestine. They therefore pass intact into the colon where the intestinal microbiota ferments them. This fermentation leads to the production of short chain fatty acids.

Better understand what a fiber intake in our diet is used for

Fibers are present in different forms (cellulose, hemicellulose, pectin, gums). They are found in the fruits, vegetables or grains that we eat. The intake of fiber in our diet has beneficial effects on our health. These effects are largely due to the activity of the microorganisms that we host in our digestive tract.

These fibers increase motor skills in the digestive tract, prevent constipation, and help control diverticular disease. Fiber helps eliminate carcinogens produced by bacteria in the large intestine. Epidemiological studies strongly suggest an association between colon cancer and low fiber consumption, as well as a beneficial effect of fibers on functional pathologies of the intestine, on Crohn’s disease, obesity or hemorrhoids. Soluble fiber (found in fruits, vegetables, oats, barley and legumes) reduces the postprandial rise in blood sugar and insulin and can lower cholesterol levels.

The beneficial health effects of dietary fiber are mediated by short-chain fatty acids which have shown their immunomodulatory and anti-inflammatory properties, notably by activating the G protein-coupled receptor in neutrophils which is involved in the recruitment of mediators of inflammation and immunity cells and by inhibiting the activity of histone deacetylases involved in inflammation gene expression and monocyte recruitment. In addition, short-chain fatty acids increase the response of regulatory T lymphocytes and the secretion of immunoglobulins A but also promote the production of interleukin 18 involved in the integrity of the epithelial barrier.

The role of the colonic microbiota

The colon or large intestine is the terminal part of our digestive tract, mainly dedicated to the absorption of water. It is also responsible for breaking down food compounds that have not been digested and absorbed upstream in the stomach and small intestine. This digestive compartment is very dense in microorganisms and it is they (and not our own enzymes) that metabolize food residues.

Indeed, one of the main functions of this colonic microbial community is to degrade and then ferment dietary fibers.

Natural sources of dietary fiber

Grain foods are the main source of energy in our diet. They are the main supplier of dietary fiber in the Western diet. However, whole grain products are not yet widely accepted despite their nutritional value. Indeed, the increase in the fiber content in cereal foods induces harmful consequences on the organoleptic level, which calls for a review of the entire chain of their production processes.

Grain foods and nutritional issues :

Grain foods are widely consumed in various forms around the world, although they may no longer form the base of the food pyramid in Western countries. Due to their alveolar structure, the matrix of cereal foods (bread, cookies, cakes, etc.) can be considered as a solid foam, since their density is much lower than that of their components.

Due to their starch and protein content, grain foods are the most important source of energy in our diet and their protein fraction provides a wide range of amino acids. These foods are already the main supplier of dietary fiber in the Western diet, although whole grain products are not yet widely accepted or consumed, despite their high dietary fiber and micronutrient content.

But then, why talk about dietary fiber in fruits?

Certain fruits, especially tropical ones, are indeed rich in cellulose, gum, polysaccharide and sometimes lignin. Everyone knows that a fruit, especially insufficiently ripe, that is to say less rich in easily digestible carbohydrates, is an excellent laxative because it provides water, allows the food bowl to retain water and facilitates transit.

What are the pharmacological properties of fibers ?

These are firstly; the retention of water by cellulose, hemicellulose, pectin (not lignin), therefore the more viscous consistency and the greater volume of the matter of the food bolus after digestion of the products solubilized by the gastric juice and the enzymes of the small intestine.

Secondly; the release of short-chain fatty acids by microbial attack on cellulose and hemicelluloses which have somatic power, therefore retain water and increase hydration of the stool; certain fibers, gums, mucilages and lignin, exhibit a capacity for adsorption of bile salts in the colon, which increases hepatic synthesis and lowers the blood level of triglycerides and cholesterol.

Calorie intake is very low since these fibers are poorly digested in the colon by microbial means. On the other hand, one can note an adsorption with elimination of fats, proteins and certain cations. In fact, some have seen it, because of our diet too rich in calories and fat, a possibility of avoiding atherosclerosis and coronary heart disease.

But before proposing a diet using these dietary fibers, wouldn’t it be wiser to simply lower our intake of sugars and lipids?

Finally, the biggest benefit shown is the increase in the volume and hydration of the bolus. In short, a laxative power allowing the evacuation of this bowl, and, in fact, preventing diverticular disease of the colon, which often causes cancer of the latter in a few years. This phenomenon has been observed in various countries whose diets are too rich but poor in fiber.

Conclusion :

Dietary fiber is resistant to digestion and absorption. Prebiotics are fermentable dietary fibers that benefit health through their effects on the composition and activity of the microbiome. Consuming dietary fiber confers a variety of physiological benefits. Children who are encouraged to eat foods high in fiber are taught to eat a diet high in nutrients. Introducing various sources of dietary fiber to young children helps crystallize their future food choices and diversify their gut microbiota. Low fiber intake leads to a higher prevalence of constipation and obesity.

The usual Western diet is low in fiber (around 12g / day) due to high consumption of highly refined cereal flours and low consumption of fruits and vegetables. It is generally recommended to increase the intake of fiber, up to 30g / day, by increasing the intake of vegetables, fruits and grains rich in fiber.

However, too much fiber intake can reduce the absorption of certain minerals.

Sources :

Fardet A, Rock E. From a reductionist to a holistic approach in preventive nutrition to define new and more ethical paradigms. Healthcare (Basel). 2015
Gibson L.J., Ashby M.F., 1997. Cellular solids, structure and properties. Cambridge Press University
DURLACH (J.). Déficit en fibres alimentaires et pathologie générale : athérosclérose, obésité et diabète. Gaz. Med. Fr., 28 avr. 1978
BURKITT (D.P.). Sorne diseases characteristic of modern civilisation. Bril. Med. J., 1973