Dietary fiber can be a double-edged sword for your IBS. Not only the type of fiber you eat can affect your IBS, but also the amount you eat and the type of your IBS plays a major rule.

? Today I will try to simplify the complex relationship between fiber and IBS. And answer the questions running in your head about fiber? like:

  • Is fiber good or bad for my specific IBS type?
  • How can fiber hurt my IBS?
  • When and how to take the appropriate type of fiber?
  • when should I take fiber supplements?

ibs and fiber

(1) Research Says Fiber is not always afriend of IBS.

The exact cause of IBS is still UNKNOWN. IBS is a ?functional? disorder, meaning that we couldn?t define a certain lesion in your gut.

we have only “theories” linking IBS to:

  • Small intestinal bacterial overgrowth.
  • Inflammation of your gut mucosa.
  • Psychological stress.
  • Deficient or increased fiber intake.
  • Increased your colon sensitivity to gas.

It is widely accepted that IBS is usually caused by a combination of those. one of these factors is dietary fiber.

Some studies have shown that deficient fiber intake may be the cause of IBS, especially IBS-constipation. While other studies linked specific types of fiber to some IBS symptoms. The highly fermentable short-chain soluble fibers are accused of distension and bloating in IBS.

The relation is complex and science still poorly understands this relation. Fiber is a real ?double-edged sword? that can relive or worsen your IBS.?

This is because:

  • The response to fiber is highly different between IBS patients (even to the same amount and type of fiber).
  • The research still deficient and poorly understands this relation.
  • Different types of fiber can be found at the same diet source.
  • No accurate calculations of the amount and type of fibers in your diet.

But I will do my best to make you understand what can help and what can hurt your IBS.

(2) Different Types Of Fiber Have Different Effects On Your Ibs.

The fiber in your diet is divided into 2 main types:?

  • Soluble fibers: dissolves in water and forms gel, but gets fermented by gut bacteria producing gas.
  • Insoluble fibers: cannot be digested by your intestine enzymes. It attracts water making stool looser and also, slows down the absorption of sugar and cholesterol.

But Solubility is not the only factor that determines the effect of fiber in your IBS.?

Fermentability is more important. (for soluble fibers).

Fermentation is the digestion of fibers by your gut bacteria producing gas. Fermentation usually occurs in soluble fibers (digestible fibers). The rate and degree of fermentation are what determines whether the fiber can hurt or benefit your IBS:

  • Highly fermentable soluble fibers:?

they are the short-chain types of fibers (monosaccharides, disaccharides, and oligosaccharides).

FODMAPS (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) are actually soluble fibers; the bad type of soluble fibers.

Because they are short-chain, they have digested more easily and more rapidly by your gut microbiota. This results in rapid gas production. Rapid gas production increases abdominal pain/colics and distension/bloating.

  • Moderately fermentable soluble fibers:?

The Long-chain soluble fibers are more difficult for gut bacteria to digest, so it is slowly and moderately fermented.?

So you can obtain the benefits of soluble fibers without experiencing the bad effects of rapid fermentation.?

An example of this is ?Psyllium?. Psyllium is a long-chain moderately fermentable soluble fiber. It is considered good for your IBS, especially if you have IBS-constipation.?


Actually there are three types of fibers, not two:

  1. The insoluble fibers.
  2. The soluble highly fermentable fibers. (AKA FODMAPS)
  3. The soluble moderately fermentable fibers.

Below, I will explain to you the food sources, pros, and cons of each type.

(3)?Insoluble Fiber Is a real double-edged sword for IBS.

As we explained before, Insoluble fiber passes undigested through your intestine.

Insoluble fibers are known for their laxative effects. But its role in IBS is still controversial.

  • Types and Sources of insoluble fibers:

1- cellulose: found in cereals, fruit, vegetables (in all plants in general)

2- Hemicellulose: found in cereals, bran, timber, legumes like wheat, barley, rye, and oat.

2- lignins: in stones of fruits, vegetables (filaments of the garden bean), cereals

3- Resistant starch: high amylose corn, barley, high amylose wheat, legumes, raw bananas, cooked and cooled pasta and potatoes.

  • Benefits Of Insoluble Fibers (In General):

  • Helps with constipation: as it adds bulk to stools and increases its water content, so the stool becomes less hard and more easy to pass.
  • Helps in regulating bowel movements: eating regular amounts of insoluble fiber prevents the ups and downs in your bowel movements.
  • Helps weight loss: it increases the amount of food without increasing calories, this fills your stomach faster, providing early satiety.
  • Regulates blood sugar: it slows down the absorption of sugar, especially if you have diabetes mellitus.
  • What Does the Research Say About Insoluble Fiber And IBS?

Although research supports the beneficial effects of insoluble fiber, its role in irritable bowel syndrome is still controversial.

No solid evidence that insoluble fiber improves the symptoms of IBS. a famous clinical trial assessed bran (insoluble fiber) effect on overall IBS symptoms. The insoluble fiber bran was found NOT EFFECTIVE in improving IBS symptoms.?

Other gastroenterologists go even more extreme; the British doctor Dr. Peter J Whorwell wrote that he was surprized by the over-estimation of the benefits of insolube fiber in IBS in Public press.

Also, He thinks that the total restriction of certain dietary fiber like bran and brown bread was found very effective in reducing symptoms of IBS among his patients.?

Read the full article at the British Medical Journal: ? The Problem Of Insoluble Fiber And IBS?

I believe in the words of Dr. Peter, and So Do I with my IBS patients. I am consistently noticing that Many new IBS flare-ups are caused by eating too much of insoluble fiber.

Looking at the general benefits of insoluble fibers, it is a must that you eat them, but this should be in modest amounts, increasing insoluble fiber my harm your IBS.

(4) The Short-chain Highly Fermentable Soluble Fiber Is A Definite Enemy For Your IBS.

The short-chain highly fermentable fibers are a type of soluble fibers. Rsearch found that this type of fiber is bad for IBS.

They are rapidly fermented inside your intestine producing more gas. The excess gases usually worsen your IBS causing cramps, bloating and distention.

These short-chain fibers together with another group of substances called ?polyols? form what is called the ?FODMAP? group of foods. Restricting these ?FODMAPs? will subsequently improve your IBS symptoms.?

Types And Food Sources:

  • Oligosaccharides: Refers to compounds called fructans and galacto-saccharides present in wheat, barley,? rye, onion, garlic, and legumes.
  • Disaccharides: Refers to fructose sugar present in milk ice cream custard and yogurt
  • Monosaccharides: Refers to free fructose present in Apples, pears, mangoes, cherries, watermelon, asparagus, sugar snap peas, honey, high-fructose corn syrup.

(5) The Long-chain Moderately Fermentable Soluble Fiber Is A Potential Friend.

The long-chain soluble fiber is slowly fermented. When taken in the right way and the suitable amount may benefit your IBS, especially if you have constipation-predominant IBS.?

Benefits of soluble fibers include:

  • Like insoluble fibers, It adds bulk to stools, helps with the regulation of your bowel movement and prolonged satiety.
  • It dissolves in water. Forming viscous gel helping with both diarrhea and constipation (theoretically).?
  • Usually soluble fibers are good for diarrhea in general but not IBS-Diarrhea. Scientific evidence suggests only the long-chain soluble fibers (e.g. Psyllium) are of benefit in IBS-Constipation.
  • Additionally, it slows the absorption of sugar and cholesterol protecting from diabetes, atherosclerosis and cardiac diseases.

Sources of soluble fibers:?

  • psyllium seed husks (a mucilage soluble fiber) and flax seeds.
  • legumes (peas, soybeans, lupins and other beans)
  • some fruits (including figs, avocados, plums, prunes, berries, ripe bananas, and the skin of apples, quinces, and pears)
  • oats, rye, chia, and barley
  • certain vegetables such as broccoli, carrots, and Jerusalem artichokes
  • nuts, with almonds being the highest in dietary fiber
  • root tubers and root vegetables such as sweet potatoes and onions (skins of these are sources of insoluble fiber also).

(6) 6 reasons why adjusting your Dietary fiber for IBS is challenging!

1- Foods usually contain a mix of the 3 types of fiber (insoluble, long-chain, and short-chain soluble fibers).

2-?Most dietary references of the internet doesn?t accurately differentiate between specific types of fiber in foods.

3- Response to dietary fiber is extremely variable between different IBS patients.

4- The exact amount of fiber that can benefit your IBS without causing harm is unknown and variable from one patient to another.

5- Using fiber in improving IBS symptoms is still controversial in research, the only exception is that the use of soluble fiber psyllium husk is recommended in patients with IBS-C.

6- The amount of dietary fiber in many foods changes, depending on whether they are raw, cooked, stewed, steamed, fried or baked.

(7) 6 Golden Rules To Safely Eat Fiber With IBS.

Because we -IBS sufferers-? are not the same, no single advice will apply to all of us. That is why I am starting all my advice with “IF”:

1- IF you think you get flare-ups after eating insoluble fiber > start elimination diet plan (exclude all sorts of insoluble fiber from your diet for 12 weeks).

2- IF you think you are not getting enough fiber in your diet: try to gradually increase fiber in your diet (start low and go slow)

NOTE: sudden increase of dietary fiber may increase your IBS symptoms even with the useful types of soluble fiber.

3- IF you eat refined grains: try to shift to the whole grain (e.g. eating brown rice instead of white rice).?

4- IF you have IBS-C, gradual increasing fiber in your diet should be tried, or you may take supplements especially Psyllium. (see below).

5- IF you eat fruits and vegetables, try to eat them with peels or skins intact when possible.

6- Accurate medical and dietary history by your doctor or dietitian is key to make fiber work for your IBS. (No “IF” here :D)

(8) Fiber supplements is not for all IBS patients.

Fiber supplements are available as over the counter drugs. You can take them without a prescription.


Fiber supplements are not beneficial for all conditions and symptoms of IBS. I usually recommend a trial of dietary fiber modification at first.

Many types of fiber supplements are available, the two most commonly used are:

  • Psyllium husk (Metamucil?).
  • Methylcellulose (Citrucel?).

Both types are beneficial to IBS, especially IBS-C with the basic difference between them is that methylcellulose produces less gas and bloating than psyllium.

You should start fiber supplement for your IBS if:

  • You have IBS-Constipation.
  • You fail to obtain sufficient dietary fiber (you can?t tolerate increasing dietary fiber).

Fiber supplements can be ineffective or even harmful if:

  • Your IBS is mainly with diarrhea and excessive gas (distension).
  • You already obtain the recommended amount of dietary fiber (about 20 to 30 grams per day).
  • Fiber supplement consistently worsens your IBS despite following the recommended doses.

Main uses of famous fiber supplements for IBS:

Psyllium is used to decrease:

  • Constipation
  • Abdominal pain (cramps).
  • In some conditions of diarrhea not associated with gas and bloating.

Methylcellulose is used in cases of:

  • Constipation
  • Abdominal colics
  • Gas and bloating
  • Sense of incomplete defecation.

Because of the high variability of response to fiber and different causes of our IBS, Never forget to discuss these options with your doctor and dietitian.?

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