Saturday 24 June 2017

The importance of dietary fibres

Until a few years ago, it was thought that dietary fibres simply acted as ballast in the diet. But because of soluble fibres, resistant starch and especially prebiotics, we now look at that very differently. A brief overview about the importance of fibres.


Dietary fibres are carbohydrates and are subdivided into digestible and indigestible fibres. Indigestible fibres are mainly found in vegetables, fruit, legumes, whole grain products, potatoes and nuts. Digestible fibres can be found in, for example, oats, onions, apples, linseed, guar, chicory, banana and seaweed. Adequate intake of both types is essential for good health.


Indigestible dietary fibres

Cellulose is perhaps the best known dietary fibre. Cellulose occurs in the cell wall, along with hemicellulose and lignin. The cell wall provides extra protection against mechanical stressors of the plant and makes the cell ‘hard’. Cellulose is a glucose polymer, which cannot be digested by people. That also applies to hemicellulose. This polymer comprises several types of monosaccharides. In the plant, hemicellulose forms a matrix, embedded in which is the cellulose. Lignin is not a carbohydrate, however is considered to be a dietary fibre.


Cellulose and lignin are not soluble in water, hemicellulose is partially soluble. Because of their specific characteristics, the three substances play an essential role in maintaining health in general and gut health in particular; they act as ‘brushes’ that scrape the intestinal wall clean. This helps prevent pathological micro-organisms from attaching to the wall and accelerates the transit through the intestine. Optimal transit speed reduces the toxic load on the alimentary canal and therefore has a beneficial effect on health.


Fibres more important than thought

Opinions amongst scientists regarding fibres have changed significantly in recent years. The presence of soluble fibres (in oats, wheat and rye), resistant starch and especially those in prebiotics (inulin, oligofructose, galacto-oligosaccharides, lactulose, lactitol) have shaken up the ‘fibre landscape’ considerably. For example, it is now known that these nutrients have more of a regulatory function and, in relation to intestinal motility, accelerate or delay the intestinal transit time. In the small intestine, they are not digested, however they are fermentable and are therefore broken down through the actions of the bacterial gut flora. Result: in adults, this leads to an alternating increase in bowel movement bulk, which is positively correlated with the speed of intestinal transit.


The regulating effect is brought about by various mechanisms of action, such as:

  • the osmotic capacity;
  • an increase in bacterial biomass;
  • stimulation of intestinal motility caused by fermentation end products (such as, for example, short-chain fatty acids);
  • increased sodium and water absorption in the proximal intestine.


In short, all of this suggests that to prevent a ‘derailment’ of the bowel transit, it is absolutely necessary to eat high-fibre foods. Variation is an essential element of this, in order to derive maximum benefit from the regulating and synergistic effect of the various fibres.


Soluble fibres

Pectin (for example, in oats, onions and apples), mucilages (for example, in psyllium and linseed), gums (for example, in guar), inulin (for example in chicory), oligofructose (for example, in bananas) and polysaccharides from seaweed (for example agar) belong to the soluble fibre group. These dietary fibres are viscous or gel-forming and can be broken down by bacteria in the colon. The fibres can be found in the vacuole of the cells. A vacuole is a cell membrane-bound compartment of the cytoplasm.


The functions of vacuoles are:


  • Removal of excess cellular material;
  • Isolation of toxic substances that could damage the cell;
  • Storage of waste products;
  • Retention of hydrostatic pressure inside the cell, also known as turgor;
  • Retention of a relatively acidic environment in the cell;
  • Excretion of unwanted materials.


Fibres have exactly the same functions in the gut.


Inulin and FOS

The best known and most researched soluble fibres are inulin and fructooligosaccharide (FOS); fibres that are built up from fructose polymers. They occur in the roots of chicory, Jerusalem artichoke, dahlia, dandelion, scorzonera, onion, leek and artichoke. These plant fibres are poorly digested and, like the insoluble fibres, increase the volume of the faeces, enhance satiety and are a breeding ground for healthy gut bacteria.


One of the main bacterial colonies within healthy gut flora is the colony of bifidobacteria. Bifidobacteria are capable of breaking down the dietary fibres into acetate (acetic acid) and lactate (lactic acid), which generate ATP (energy) and a number of degradation products. In turn, these degradation products are responsible for the growth of bifidobacteria, a sort of self-sustaining body system. The lactic acid that is produced helps to maintain the correct pH within the various components of the alimentary canal. Acetate can be absorbed in the ATP-producing citric acid cycle of epithelial cells of the gut wall.


Fibres and GABA

A compound called putrescine is one of the degradation products of dietary fibres. Putrescine can be converted into the neurotransmitter gamma-amino butyric acid (GABA). GABA is one of the most important neurotransmitters of the enteric nervous system - ENS) and is responsible for regulating peristalsis and for the excretion of substances like gastrin and acetylcholine.


Within the ENS, GABA has both an activating and inhibiting function; GABA only has an inhibitory effect within the central nervous system. A GABA deficiency (through a shortage of dietary fibres or prebiotics and therefore a deficiency of health-promoting bacteria) leads to disruption of peristalsis and the formation of gastric ulcers (deficiency of substances that protect the stomach and gut wall). Dietary fibres are therefore essential for optimal nutrition when providing natural healthcare.


The knowledge in this article originates from our Nutritional Therapy in accordance with clinical PNI course. This course will provide you with a solid base of essential knowledge about nutrition, exercise and supplementation in relation to chronic diseases within our current Western Society. More information.