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Does Fiber Help Diarrhea or Make It Worse? – Explained

Fiber… Some say that it helps diarrhea while others say that it makes it worse, so which is it?

If you suffer from diarrhea should you be hunting through the grocery store for foods containing high amounts of fiber or should you be trying to avoid it?

No one wants to have diarrhea. Frequent trips to the bathroom, a whole day's plans being messed up, a hard time getting work done… These are all side effects that come from loose and watery stools, a.k.a. diarrhea.

We wish that there was a simple answer to give, such as "avoid fiber" or "eat more fiber", but unfortunately the answer is a bit more complicated than that.

There are 2 different types of fiber, and these 2 types have different effects on diarrhea…

Insoluble vs Soluble Fiber


Insoluble fiber, as you can imagine, is not soluble in water. This type of fiber goes through the G.I. tract unaffected and ends up in the colon, where it then can be fermented by the healthy bacteria living there.

This type of fiber, because it does not absorb water, is the kind you would want to avoid it if you have diarrhea.

  • Speeds up bowel movement transit time
  • Helps balance pH level in the GI tract

Some sources of insoluble fiber include…

  • Cellulose - Found in grains, seeds, nuts, fruit & vegetable skins
  • Lignin - Found in grain, nuts, seeds, fruit & vegetable skins


And then there is soluble fiber, which is the type of fiber that is soluble in water. This type of fiber also goes through the G.I. tract and is fermented by bacteria, but there is a key difference… It absorbs water.

Soluble fiber absorbs water in the intestines and turns into a gelatinous substance, adding bulk and helping firm up loose stool.

  • Absorbs water and firms up stool
  • Reduces transit time of bowel movements
  • Lowers cholesterol and regulates blood sugar level

Some good sources of this type of fiber include…

  • Pectin - Commonly found in fruits
  • Resistant Starch - Found in unripe bananas and oats

Soluble Fiber Seems to Be Good All-Around, While Insoluble Fiber Isn't Recommended for Those With Diarrhea

Fiber does not get digested and because of this can cause an osmotic effect, where the undigested particles attract more water into the colon, which is great for constipation but not so great for diarrhea.

The reason soluble fiber can help with both is because, not only does it attract water into the colon, but it also absorbs water, which leads to a healthy balance of stool overall. Whereas insoluble fiber just attracts more water and does not absorb, leading to looser and more watery stool.

In a 2015 study 87 patients who had IBS and were prone to developing diarrhea received 24 g of pectin (soluble fiber) for a 6 week treatment. The results were positive and that the patients'symptoms had reduced.

On the flip-side, a separate 2014 study conducted on 80 patients with constipation experimented by giving them 24 g of pectin per day for 4 weeks. The results here were that it also alleviates symptoms of constipation.

Pretty interesting, but it makes sense.

As far as insoluble fiber goes, it is only shown to help treat constipation, but have negative effects when it comes to diarrhea if consumed in too high amounts.

Fiber Is Often The Cause of Diarrhea

There are numerous causes of diarrhea. One could be experiencing diarrhea from an allergy, an intolerance to some substance they have eaten, too much insoluble fiber, a bacterial infection, and so on. HOWEVER, having an imbalance of fiber definitely seems to be one of the most common causes.

Insoluble fiber, as you already know, is great for treating constipation but when someone eats too much of it, it can lead to diarrhea.

The good thing is that having diarrhea from a fiber imbalance is not a big deal. All you have to do is make changes to your diet and you will see results very quickly.

How Much Fiber Should You Get Per Day?

Most Americans only get around 15 g of fiber per day which is not enough. The daily recommended amount ranges from 25 to 30 g per day.

The reason for this mostly comes from Americans eating too much processed foods as well as just not knowing what they should be eating. For example, the trendy gluten-free diet will likely result in very low fiber intake, but most people on this diet don't know and/or care.

Not only is getting the recommended amount of daily fiber good for regular bowel movements, but it is also good for gut bacteria, which can impact your overall health.

What to Eat for Diarrhea

It would be nice if there were foods that only contained in soluble fiber and that only contains soluble fiber. However, there isn't. All plant foods contain a mixture of both insoluble and soluble fiber.

So if you are going to eat real food and want to get as much soluble fiber as possible you are also going to have to take in some insoluble fiber. And unfortunately, the insoluble fiber is always higher than the amount of soluble fiber.

One good recommendation if you have diarrhea and believe it is caused by your fiber intake would be to try the BRAT diet. BRAT stands for bananas, rice, applesauce, and toast.

This diet, while not the most effective, is easy to follow and commonly used. The goal of this diet is to provide very little overall fiber and attack diarrhea from an overall reduction standpoint. This wouldn't be a great diet to follow for the rest of your life, but it may be worth giving a try to see if it can put an end to your ridiculously frequent bathroom visits.

Something else you may want to look into adding to your diet are Brussels sprouts. Brussels sprouts are a very great source of soluble fiber, one of the best.

Here are other foods that help with diarrhea.

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Starting his writing career in 2015, Kyle is a leading contributor here at GutAdvisor, and for good reason. Having a passion for health and the awareness that proper digestion plays a key role one's overall well-being, he regularly keeps the community informed with valuable information regarding gut health.

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  1. Grammar in last few paragraphs is pretty careless. There aren’t foods**** not there isn’t foods. And some other typos… in soluble fiber? I almost could trust this source but not so much.

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