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