Although dietary fibre is not considered a 'nutrient', it is essential for our diet and, therefore, its intake has been increasingly studied.
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Previously, the importance of dietary fibre was solely accredited to improving bowel function, but recent research has shown that an adequate intake of dietary fibre may reduce the risk of developing several chronic diseases such as: coronary artery disease (CAD) (3), cerebrovascular accident (CVA) (4), hypertension (HT) (5), diabetes mellitus (DM) (6) and some gastrointestinal disorders (7). Inversely, an increase in fibre intake enhances cholesterol levels in the blood (8, 9), reduces pressure (5), improves glycemic control in patients with diabetes mellitus (10), assists in reducing body weight (11), and acts to improve the immunological system (12).

Fibres are carbohydrates that cannot be digested by the body. They are polysaccharides and phenolic polymers found in the composition of some foods. They influence the gastrointestinal tract’s movements, improving our digestive function and reducing the risk of a number of diseases. This is because they resist digestion by human-made enzymes as they travel down the digestive tract, and are either, partially digested by microbiota in the colon, or relatively unaltered and excreted in stool. So, fibre helps in sustaining healthy gut microbiota, which is related to: the protection against colonization and proliferation of bacterial pathogens, the proper functioning of the immune system, and the proper absorption of nutrients, proving to be fundamental to health (13-16). The World Health Organization (WHO) recommends a daily intake of at least 25g of fibre. However, the increased consumption of processed and refined foods has lessened this daily intake, due to the loss of certain nutrients, including fibres, during processing.

Dietary fibre is classified into two groups depending on its solubility profile. It can be found in fruits, vegetables, legumes and whole-grains.

SOLUBLE FIBERS

Pectins, mucilages, gums (gum Arabic and guar gum), inulin, FOS (fructooligo-saccharides), beta-glucans, psyllium and hemicellulose type A. This fibre has the ability to bind to water and form gels (reason for which they are called soluble). In the gastrointestinal tract, it delays gastric emptying and bowel transit time; reduces the rate of glucose and cholesterol absorption; is a substrate of bacterial fermentation that results in gases (hydrogen, methane and carbon dioxide); and is transformed into short chain fatty acids (SCFAs) which serve as food for the healthy intestinal flora and enterocytes, which are fundamental to intestinal metabolism (13, 18, 20). It is found primarily in fruits and vegetables, but also in cereals (oats and barley) and legumes (beans, chickpeas, lentils and peas) (20).

Main Metabolic Effects Of Soluble Fibers (13, 18, 19, 20)*:

  • Slows gastric emptying which may give the feeling of satiety;
  • Alters metabolism in the colon through the production of SCFAs;
  • Modulates gastrointestinal motility;
  • Promotes the development of gut microbiota or flora;
  • Provides energy for the intestinal mucosa;
  • Lowers the pH of the colon, hindering the emergence of pathogenic bacteria;
  • Improves protection against infection;
  • Increases glucose tolerance.

*Excess soluble fiber (above 50 grams) can cause increased intestinal fermentation with intense formation of gases and even diarrhea.

INSOLUBLE FIBERS

Cellulose fibres (plant-based fibres), hemicellulose type B, resistant starch and lignin. It forms part of the external structure plant cells. It has a mechanical effect in the gastrointestinal tract. It is hardly fermentable and accelerates bowel transit time due to the absorption of water (15). Thus, it increases the bulk and softness of stool, reducing intestinal constipation. Since it is hardly fermentable, insoluble fibre does not cause the formation of gas and diarrhea, but if consumed in large amounts it may result in bulky stool. It is important to remember that for insoluble fibre to fulfil its role in the body, the intake of plenty of fluids is required. It is found primarily in vegetables, wheat bran, oats, rice and whole grains.

IMPROVED BOWEL FUNCTION = IMPROVED IMMUNITY

Soluble fibre dissolves in water. Insoluble fibre does not. To some extent this difference determines their functions in the body and their health benefits, but the two equally act on the speed of bowel transit. Soluble fibre leads to reactions of fermentation, producing high concentrations of specific substances, called short-chain fatty acids (SCFAs). These elements are the main drivers of waste product movement and they regulate smooth bowel transit. In the large intestine, SCFAs function as the power source to the mucosa and as protective agents of various diseases such as diarrhea, inflammatory bowel disease and colon cancer. On the other hand, soluble fibres form a smooth surface layer along the small intestinal mucosa and serve as barrier in the absorption of some nutrients, delaying the essential metabolism of carbohydrates and fat. This contributes greatly to the stabilization of energy metabolism, controlling sudden increases in glucose levels. Previous studies have also shown that the ingestion of soluble fibre contributes in lowering levels of cholesterol by reducing the absorption of bile salts in the small intestine.

It is also important to note that one of the most interesting properties of soluble fibre is fermentation. Fermented fibres are converted into nutrients necessary for a better development of the lactobacilli and bifidobacteria, favourably increasing the beneficial gut microbiota, which in turn inhibits the growth of pathogenic (malignant) bacteria. Thus, the organ’s immunological system is also strengthened, preventing gastrointestinal infection and even of colon cancer.

METABOLIC EFFECTS OF INSOLUBLE FIBER (15-18):

  • Increases the bulk and softness of the stool;
  • Increases the frequency of bowel movements and reduces transit time in the colon;
  • Reduces constipation;
  • It absorbs water;
  • It is hardly fermentable;
  • It is not slimy;
  • Intensifies protection against bacterial infection.

BEYOND SATIETY

Researchers at Imperial College in London (England), found that the secret to appetite suppression lies in a molecule known as acetate, released in the intestine during fibre intake (21).

Experiments with mice proved that when the acetate accumulates in the hypothalamus (the brain region that regulates hunger), a series of chemical reactions affect neurons, reducing appetite. During the study, when the acetate was injected directly into the bloodstream, intestine or brain of mice, there was a reduction in food consumption. As this substance remains active only for a short period of time in the body, scientists believe that only a single "acetate pill " is necessary to prolong the effect of the substance in the organism (21).

The study also examined the effects of one type of fibre called inulin, originating from chicory and sugar beet, added to cereal bars. During the experiment, it was found that animals subjected to a diet rich in fat and inulin ate less and, consequently, gained less weight than the mice who consumed a diet rich in fat, but without inulin (21).

CARDIOVASCULAR PROTECTION

A recent study evaluated the association between dietary fibre intake versus cardiovascular mortality. The results revealed that those who consumed more fibre have on average a 25% lower all cause and cardiovascular mortality, not just heart disease, in comparison with individuals who did not consume fibres (22). Another study showed that individuals who increased their fibre intake after suffering a myocardial infarction also reduced the risk of death from any cause, including new cardiovascular events, as reported by Time magazine (23):

“Every 10g increase in dietary fibre intake per day after a heart attack was associated with a 15% lower risk of death from any cause during the study period. It is the first study to suggest that patients with heart attacks benefit from the addition of fibre in their daily diet. Studies show that high-fibre foods can fight inflammation, a potential trigger for heart attacks, and keeping lower LDL cholesterol levels, which can build up in the heart arteries.” (24)

This research also found an inverse association between fibre intake and heart attacks. Those who eat a high fibre diet have a 40% lower risk of heart disease. Research published in the past year, also found that for every 7 grams more fibre one consumes daily, the risk of cerebral vascular accident (CVA) is reduced by 7% (25). This amounts to increasing ones daily intake of fruits and vegetables by two additional portions.

FIBRE: GUT MICROBIOTA NUTRITION

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To prevent fibre deficit, a more complete, varied and balanced diet is required, containing bran, oatmeal, fruits, nuts, vegetables and grains.

Health begins with proper nutrition and digestion, and our gut microbiota help a lot in achieving this. So we need to feed our intestinal flora and ensure proper functioning of the intestine. Studies prove and quantify that the benefits of having a diet rich in fibre go far beyond the intestine. But as this is not always possible, the use of food supplements rich in fibre is often necessary. Among the characteristics of a good fibre supplement, it must have a variety of soluble and insoluble fibres sources emulating nature.

References:
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