Excess of Dietary Fiber

Excess of Dietary Fiber


The excess of dietary fiber  must be estimated in relation to the evaluation of the inter- and intra-individual factors which determine the subjective variability.

Recommended intake

What is the Normally Recommended Fiber Intake?

According to the most reliable bibliographic sources,  dietary fiber  should be introduced in the diet in quantities of around 30g/day; this value represents the sum of the  soluble  and insoluble fibrous components such as:  cellulose , hemicelluloses, pectins ,  rubber  and lignins.

Soluble and insoluble fibers

Role of soluble and insoluble fibers and foods containing them

The effect of soluble fiber on the  faeces  is of the gelling type, while that of insoluble fiber is of the fermenting type.
The excess of fiber is generally perceived by the appearance of some symptoms attributable to the excessive production of  gas , therefore  meteorism ,  abdominal distension ,  flatulence ,  cramps  and a NON-physiological increase in faecal evacuation  .
The sources of dietary fiber are:

  • Vegetables  ( cereals ,  legumes ,  vegetables  and  fruit );
  • Mushrooms.

Soluble fiber   comes mainly from vegetables and fruit, while  insoluble fiber  comes from cereals. The latter, in addition to being present in greater quantities in foods (especially wholemeal ones  ), has the advantage of constituting a category of   widely consumed  foods : pasta ,  bread ,  pizza  and all derivatives.

Dietary functions

Functions and Effects of Fibers

The correct intake of dietary fiber has several  positive functional  and metabolic effects:

  • Intestinal regulation  and increase of  prebiotics
  • Waste dilution correlated with reduction in  colorectal cancer incidence
  • Glycemic modulation   to slow down  glucose absorption  (reduction of the incidence risk of  type 2 diabetes mellitus )
  • Reduction of lipid absorption of fatty  acids   and  cholesterol  (reduction of the risk of  dyslipidemia  and  coronary artery disease )
  • Reduction of the risk of  constipation  and  diverticulosis , prevention of  diverticulitis , prevention of typical acute inflammatory bowel diseases
  • Increased gastric satiety.

Risks Associated with Excess

Is Too Much Fiber Bad?

The excess of dietary fiber is the consequence of inappropriate nutritional conduct; first of all, the thoughtless integration  of concentrated products. These, commonly obtained from the compression of  bran  or other cereal processing waste, can negatively affect the symptoms of the  irritable colon  , worsening the undesirable effects.

On the contrary, the rational increase of the intake of soluble fiber  deriving from food  favors the reduction of the irritation of the  colonic mucosa  and lowers the  faecal pH  promoting (also thanks to some  PREbiotic oligosaccharides ) the intestinal PRObiotic  selection   to the detriment of the putrescent strains.

However, excess dietary fiber from vegetables and fruit can also negatively affect health. Some dietary theories (such as the  Zone , the  Paleo  , etc.) promote the free consumption of these foods, praising their beneficial effects and omitting their side effects; among the latter, the following undoubtedly stand out:

  • Tendency towards  generic intestinal malabsorption  extended to all nutritional components of the diet:  carbohydrates ,  amino acids , lipids ,  mineral salts  and  vitamins
  • Excessive intake of  phytic acid  and  oxalic acid , chelating molecules which by binding to some ions (such as  iron  and  calcium ) prevent intestinal absorption
  • Predisposition to  dehydration  in case the excess of fiber induces  osmotic diarrhea .

In the long term, excess dietary fiber can cause  malnutrition  or at least alteration of the overall dietary balance.


  • Levels of Recommended Intake of  Nutrients for the Italian population (LARN) – Italian Society of Human Nutrition (SINU) – page 87:89.


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