Too much fiber is bad: fiber supplements and side effects

Too much fiber is bad: fiber supplements and side effects
The excess of fibers  is reflected in the body with a set of  symptoms  mainly concerning the gastrointestinal system. It is a condition frequently related to too many fiber supplements or, more rarely, to an unbalanced diet because it is excessively rich in fibrous residues ( bran ,  whole grains ,  legumes ,  vegetables  and  fruit ) and probably low in  water .

Is too much fiber bad?

Fiber supplements ( viscous and non-viscous ), if taken in the context of a diet already sufficiently rich in fibrous residues, can cause an excess of fibers and the onset of some side effects. The most common fiber supplements are based on  isolated fibers , namely:

  • Beta-glucans :  easily fermentable viscous fibers  contained in barley  and oats , and produced by fungi,  yeasts ,  bacteria  and  algae ; the most common ones in the form of supplements derive from oats, mushrooms and yeasts.
  • Pectins : viscous fibers extracted from  citrus peel or apple  pulp  ; they also constitute a  gelling food additive  .
  • Inulin  and oligofructoses: they are extracted from  chicory  or synthesized from  sucrose ; they represent a fairly widespread food additive. They are highly fermentable and have a  prebiotic function  on  bifidobacteria .
  • Guar gum : viscous and soluble fibers which constitute a laxative product  , but are also contained in ” ready cereals  ” and other food products.
  • Psyllium : Diets low in saturated  fat  and  cholesterol,  which include 7g/day of  soluble fiber  from psyllium, may reduce the risk of  heart disease .
  • Chitosan : it is a non-  digestible glucosamine , or rather a polymer of chitin; it reduces the absorption of fats  and is available as a supplement for  weight loss  (effectiveness not proven) and for lowering cholesterol.

All these fiber supplements must be taken with plenty of water (250ml) and in the doses recommended on the  label ; too many fiber supplements and/or not enough water in the diet (abdominal tension,  abdominal cramps ,  excessive gas  and  diarrhea .

Gut side effects

There are  fiber supplements  which, more than others, determine the onset of specific symptoms associated with an excess of  dietary fiber : guar gum, inulin and oligofructose,  fructo-oligosaccharides ,  polydextrose ,  resistant starch  and psyllium. In particular, the excessive intake of Guar gum and/or psyllium, together with the insufficiency of water, can determine the intestinal obstruction  and the worsening of the symptoms in subjects with already compromised intestinal motility. Also , in people with  colorectal polyposis psyllium supplementation appears to be directly related to increasing the size of   precancerous adenomas .

Allergy side effects

It is also appropriate to specify that certain fiber supplements, although NOT in excess, require particular attention due to their allergenic potential. Chitin and chitosan, for example, which are extracted from the carapace of  crustaceans , can cause  even very serious allergic reactions in hypersensitive subjects; the same goes for the inulin extracted from chicory and for the psyllium contained in “ready cereals”.

Side effects on drug absorption

We also recall that some fiber supplements can have negative drug interactions with certain drug molecules; it is again the case of psyllium, the intake of which compromises the absorption of  lithium ,  carbamazepine  ( Tegretol ),  digoxin  ( Lanoxin ), and  warfarin  ( Coumadin ); in addition, guar gum slows the absorption of digoxin,  acetaminophen  (Tylenol) and bumetanide (Bumex), and decreases the absorption of  metformin  ( Glucophage ),  penicillin , and some glyburide formulations (Glynase). The  pectinhowever, it reduces the absorption of  lovastatin  (Mevacor) and probably also that of  clindamycin ,  tetracyclines  and digoxin.

As a precautionary measure, it is customary to recommend a distance of at least three hours between the intake of a fiber supplement and that of any drug.


Reach recommended levels while avoiding the side effects of excess fiber from too many supplements taken

The LARN (Recommended Daily Intake Levels of  Nutrients  for the Italian population) recommend reaching a fiber intake of around 30 g/day; in parallel , the Food and Nutrition Board  of the Institute of Medicine (2004)  recommends respecting a coefficient equal to 14 g of fiber for every 1000 kcal consumed, in order to lower the risk of developing  cardiovascular disease . The same institute, for adults over 50, suggests maintaining a intake of 38 g/day for men and 21 g/day for women.
These contributions are easily achievable with the diet but, if it becomes necessary, it is possible to resort to fiber supplements after having CONSULTED a food professional, who – through the food history – will be able to estimate the right daily dose  to take without incurring the side effects mentioned above.



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